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Why don’t we just open the windows? Covid-19 prevention lost in translation (bmj.com)
165 points by stmw on Nov 28, 2021 | hide | past | favorite | 288 comments

> Pumping in adequate amounts of fresh outside air, however engineered, will challenge running costs as well as carbon status.

This is wrong. Mechanical Heat Recovery Ventilation (MVHR) is a well established technology which can recycle 96% of the heat from the waste air in a house. It costs about the same to fit as a central heating system. Passive houses have very high Air Changes per Hour (ACH) compared to conventional houses, at 0.4 ACH all the air in the house is replaced approximately every 2.5 hours. All while having a whole house heat load measuring in the hundreds of watts to maintain 21ºC inside when it’s -1ºC outside. There is no reason not to put MVHR in normal houses, it’s just not possible to supply all the heat demand using air supply alone so you need a conventional heating system as well.

EDIT: Also this just goes to show what happens when people make uninformed comments on fields they don’t understand, this sentence could make a whole lot of work on reducing energy consumption in buildings get thrown out the window. I would have expected better from people that have just had 1.5 years first hand experience of the effects of misinformation on their own field.

Many non-passive house buildings have 0.4ACH or more without mechanical ventilation. The purpose of an MVHR is to provide similar trickle rates of ventilation without the high energy cost, but the goal of "opening a window" is to provide much higher airflow rates, in which case the cost would be much higher with mechanical ventilation.

It looks like 3-6ACH[1] or more is desirable to control the spread of infection. This would require very expensive MVHR systems to be installed. Realistically much larger units, probably more than one unit, as well as large ducting would need to be installed.

Such high flow rates would come with other problems: These flow rates would lead to unacceptably dry interior environments with typical heat exchangers, though there exist heat exchangers that retain some moisture. Higher flow rates also achieve lower heat exchanger efficiencies, and the power required to move the air would not be insignificant either.

[1] https://qz.com/1907977/how-to-check-air-ventilation-to-preve...

Depends on construction standards. I can’t find my source, but my understanding is that passive house is 3-4x better ACH than a typical recently built house in the UK when you take as built measurements of typical usuage patterns.

Heat recovery ventilation is an available technology and it’s not practical in the winter to sit in a house with the windows wide open, even with the heating on full so no-one will actually do it.

> my understanding is that passive house is 3-4x better ACH than a typical recently built house in the UK

Part L1A of UK building regulations stipulate an air permeability of no more than 10m3/hr/m2 of building envelope at 50pa of pressure. My home has approximately a 1:1 ratio of building envelope to volume, though this will vary a great deal. But for such a home this works out to 10ACH at 50pa. There are various studies on how to convert these measurements to natural ventilation rates, but the conversion rate is around 10-30, with the typical house being adjusted by a factor of 20, i.e. 0.5ACH, however this can be as high as 1ACH.

Some homes will be constructed to higher standards, but will not likely achieve less than half this rating.

This also ignores the presence of trickle vents inside windows in homes without mechanical ventilation, and that the majority of homes in the UK were built to lower standards - typical values for homes built prior to 2010 are 15-20m3/hr/m2.

Therefore, 0.5-1ACH is a pretty standard background ventilation rate for homes in the UK. Your typical Passivhaus home with 0.4ACH from mechanical ventilation has less ventilation than a typical home, not more.

Only very large homes built to strict modern standards and with a high interior volume to building envelope ratio could possibly have 3-4x less ventilation.

As built and as normally used measurements being the key here. Very small new build houses in the damper western parts of the uk often have problems with mould growth because of actual in everyday use ACH below building regulations design levels. It’s particularly an issue in new build social housing. People don’t open trickle vents, they turn down the extract fan timer because of fan noise and buildings are often more airtight than regulations expect and the minimum standard details are a compromise between the convenience of old conventions and prevention of cold bridging. In my experience it’s more common to fail the airtighness test by being too airtight to vent only with trickle vents than it is to come anywhere near 10@50pa. 2-3@50pa being common which drops you below the 0.4 guaranteed ACH of passive house. I’ve never seen a result over 4 @50pa. According to your calculation methodology 2-4@50pa could be anywhere between 0.07-0.4 ACH. Also, this air circulation is not designed so it just vents randomly, some rooms in the house could have very stale air while others might be quite good.

So, firstly 88% of homes were built pre-2000[1] and the regulations that resulted in these improvements came into force in 2010. Assuming the regulations instantly had the desired impact (unlikely) we're discussing around 6% of UK houses. Those built earlier (on average) achieve significantly worse than 10m3/hr/m2 air permeability of the building envelope[2]. So the vast majority of UK homes have more ventilation than a Passivhaus building, and for the purposes of the initial discussion I think this is enough to demonstrate the inadequacy of this level of ventilation for the stated purpose, else Covid spread wouldn't be a problem in the UK within the home.

It appears that for new builds latest research[3] shows an average of around 4m3/hr/m2, which is better than I expected, however the research suggests this is in part due to temporary measures by builders to achieve higher ratings than they would otherwise, and this is born out by the distribution of ratings achieved with an unlikely precipitous drop at precisely 5m3/hr/m2.

However, for houses built to this standard some form of additional ventilation is a requirement of Part F[4]. It is possible to build a house with as low as 3m3/hr/m2 and provide no additional ventilation, but it must have been designed to > 5m3/hr/m2 so this should not be common. For social housing we can assume a single bedroom home will be around 40m2 with 2.6m between floors, and the required ventilation rate is 13l/s, or 47m3/hr/m2. This is around 0.45ACH.

In fact the legal minimum rate per m2 is 1.08m3/hr, so for a typical home with 2.6m between floors this works out to 0.42ACH. So any house built to modern standards and used correctly should achieve the Passivhaus level of ventilation, unless it has tall ceilings. Certainly any UK home built with continuous mechanical ventilation is pretty comparable to Passivhaus standards for airflow.

> People don’t open trickle vents, they turn down the extract fan timer because of fan noise

People can also turn off the MVHR in a Passivhaus. I'm not sure what purpose it serves to compare correct use of a Passivhaus to incorrect use of this small fraction of UK homes.





> It costs about the same to fit as a central heating system.

Far less actually, if you use natural convection to carry the air from the inlet to the pickup points. A central heating system is a lot more expensive than your average heat exchanger+fan and a couple of pickup points and a central outlet.

New buildings in NL have these installed as standard now, mostly to combat the fungi and other humidity related problems associated with insulating a house completely.

"There is no reason not to put MVHR in normal houses"

There's no reason in new normal houses, but it is very often impossible to do it sensibly in the existing housing stock.

But then there is no reason houses shouldn't be built in factories, shipped to site and assembled. After all we already do that for hotels and the like. Yet that hasn't happened yet either.

I have experience with construction of many hotels in the US, and I have never heard of a hotel built in a factory here. It comes up in theory, but in practice everyone always goes with the usual construction methods.

Even the publicly listed tract home builders that put up developments of hundreds and thousands of homes in a couple years do not use factory built homes. It is safe to assume they know how to optimize for construction costs, and evidently, hiring local construction crews and subcontractors is still the best way.

You can get self contained through wall units and do it room by room, less efficient but cheaper to retrofit.

Hotels prefab the bathrooms typically, but not the rest of the room.

I had never heard of MVHR before, but it seems like a very good idea.

I wonder if it would work during wildfires.

The fine folks at Hufhaus would like a word. As well as quite a few others….

Yes, but they are more like a Rolls Royce than a Model T Ford.

There's no mass production, and we really need to ask why.

It sounds like they were referring to cooling air, not heating it. Is there an energy-efficient strategy for that? If not, then it doesn't seem like they were mistaken, just imprecise.

It's the same system.

Heat recovery works both ways, maintaining heat out the outlets or maintaining heat at the inlets

That's interesting. It's tempting to think that if we build houses in slightly different ways, we could have energy efficient heating and cooling systems. It seems like humidity might be a problem.

Most high end houses in Japan are already built this way. Lots of insulation with a air exchanger. They are not as low energy as passive houses, but sell brand new at prices regular families can afford.

This isn't true. Most MVHRs have a summer bypass mode in which they admit the exterior air without retaining any interior heat, but they do not cool the air entering the house.

The system in my apartment specifically calls out cooling recovery, but maybe that's not standard

Do you happen to know what make and model? The only cooling functions I have found besides summer bypass involve a separate cooling loop that ultimately relies on a heat pump. I'd be interested to read about an MVHR with this facility.

I think it’s not wrong when considered in the context of already existing large buildings (office complexes, public transit stations, department stores, restaurants, hotels, etc) as opposed to newly built individual houses (where, arguably, increased ventilation may not have that much effect on infection spread)

Or are you saying it’s still cost-efficient to retrofit in a high-rise from the day 1980s?

Most of those places are already very well ventilated. You’re not catching covid in the train station, you’re catching it while sharing 1m² with 4 other people on the train. Or because you’re in a crowded restaurant and you’re between the air extract point and the person on the table next to you who has covid. I can’t see how it would be different if the air circulation is because of open windows or mechanical ventilation in these situations.

Most high rise offices since the 50/60’s will have a mechanical ventilation system of some kind already but it may be quite energy inefficient. Any building with an existing air con system is already doing much more air changes than a building without ducted air. Offices need these systems for active cooling and heat rejection for fairly large parts of the year because the concentration of people and computers inside tends to overheat the building.

Hotels are an interesting one, I’m not an expert on hotel design but it’s possible that some hotels use positive pressure ventilation to supply air to the rooms and passive extraction through the en-suite bathrooms. In that case when you open the room door you let a blob of Covid air out into the corridor? But the corridor should probably also be at positive pressure to stop smoke from a fire in a room from blocking the escape route. Not sure about this one.

I would hypothesise that people mostly catch covid in Pubs, Clubs, Restaurants, Schools, each other’s houses and other specific hard to solve confined situations where we can’t avoid breathing each other’s exhaled air like lift cars and underground trains. If money were to be spent retrofitting heat recovery ventilation anywhere. Schools would be the best place to start.

FWIW, my office building was quite transparent about the fact that pre-pandemic, there were 1.5-2 ACH, well below the recommended 3-6 for reduction of Covid spread. They have since upgraded/reconfigured the HVAC for 4 ACH. Two of my previous offices didn’t have building-wide HVAC at all, relying on local units without configurable access to fresh air. This doesn’t invalidate your point, just highlighting that perhaps many office buildings are not up to the levels of air turnover needed without real investment.

Thank you for the insightful response!

The article is about transmission of SARS-CoV-2 in our existing environment. Not about how to build cool/heat buildings.

How many buildings have MHRV now? or could install MHRV without replacing or adding to their current heating/cooling system before it needs to be replaced - which would "challenge running costs as well as carbon status" for the next few years or more.

On this topic, HVAC often come with an "Air scavenging" feature. After reading manuals and searching online I cannot figure out what this feature actually does. Is it another name for MVHR?

In much of the world for much of the year, it doesn't get below freezing for at least part of the day. The solution to the heating problem is simple then: simply don't. Open windows when it's above 50F / 10C (to give a healthy safety margin to the water pipes) and tell people to wear sweaters.

Do this where it's possible and you'll offset the energy expenditure of heating in places were it actually earnestly gets cold. And for that matter, limit their thermostats to 50F / 10C too. Being able to wear t-shirts in the winter when there's a blizzard outside is an absurd luxury.

> Open windows when it's above 50F / 10C (to give a healthy safety margin to the water pipes) and tell people to wear sweaters.

Yeah, please don't. There's a comfortable level somewhere above that, but at 10C I wouldn't be able to function in context of work / school. With worse circulation you just end up with your hands / feet feeling like they're constantly freezing. Some teachers thought that's a good idea, but I can tell you writing in gloves just gets annoying.

>Some teachers thought that's a good idea, but I can tell you writing in gloves just gets annoying.

At risk of starting a Pythonesque masochism contest, you're lucky you were allowed gloves! Our teachers wouldn't let us wear coats or gloves when the heating broke down because "we can't see your uniform and it doesn't look smart, anyway it's not that cold". I went to a comprehensive school sandwiched between two private schools so of course my school had an institutional inferiority complex!

Also there's no way I could work well at 10C/50F, I think a company that insisted on such conditions would have trouble with resignations pretty quickly!

Dress appropriately for the season and you'll be just fine. If you wear warm clothes that cover your arms, your hands will be warmer too. Poor bloodflow to your hands is a consequence of your core loosing too much heat; your body compensates for that by reducing bloodflow to the extremities. Warm clothing makes gloves utterly unnecessary at 10C.

I’d say something similar but no, I think there are very few individuals who will not suffer in 10C, whatever the clothing.

Being physically active makes a huge difference too. With the same clothes I can be perfectly comfortable on a promenade at the same temperature that makes my fingers hurt typing at my desk.

My house is currently ~10C if I don’t activate heating. That’s miserable. My fingers get stiff and hurt a bit when at the keyboard. Even with 3 warm layers legs/4 warm layers upper. And I’m born and raised just a few miles from the Arctic circle.

People around me see me as “that guy who can handle any cold” and my breaking point for comfortable sedentary is around 15C.

Oh, and humidity does make a huge difference for how could absolute temperatures are experienced.

Is it possible other humans are different than you? Is it also possible the person wearing gloves at 10C was also wearing warmer clothing considering they bothered to use gloves in the first place?

I also do not think it is possible to describe what one should feel at 10C without specifying the humidity.

Did you really try to explain dressing appropriately to someone dealing with this issue for years? Did you expect me to go "sure, I wear winter thermals sub 10C, but this random person may have a point about dressing warmer?"

If you open windows when weather starts to warm up past 10c, you won't get a cooling to 10c indoors.

The context here is heating to comfortable temperatures. If the inside is <10C that wouldn't be even legal in many places. And the answer is - you still want to heat to something warmer.

Locally for example: "Optimum comfort for sedentary work is between 20°C and 26°C, depending on the time of year and clothing worn."

> Open windows when it's above 50F / 10C


I live in Ireland, it's not typically considered a cold climate. But it won't be above 10C this week, and probably the case for most weeks until mid-March so this advice is less globally accurate than you might imagine.

The forecasts for Dublin I'm seeing predict 10C or higher for most of Tuesday. Regardless, my advice is to keep the windows open where possible and it will offset the energy needed where it isn't. And the other component of my advice, turning down the thermostat in places where it gets cold, is certainly applicable in Ireland. You don't need 25C indoors in the winter.

I'm surprised the opening the window part is still not been mentioned much. It's been several months since Hong Kong made all establishments to maintain air flow of 25 times per hour (something like that).

It's definitely more difficult to tell colder climate countries to open windows, but really just wear a sweater or a jacket.

> just wear a sweater or a jacket.

Where I live my pipes will freeze and burst sometime in late December, but I won't find out until late February when the pipes start to thaw again.

I have a few HEPA air filters in my house. They work with whatever HVAC you have and make a difference.

If your definition of "colder climate" is around 0°C, ugh-huh. It's −15°C where I live, and it's not even winter. In December-January I expect the usual −30-40°C, with down to −50°C for short periods of time. Open your windows for more than two minutes once every few hours and die.

I live in Toronto. You can still open the windows just wear a sweater, sweatpants, and socks.

When the polar vortex happened a few years ago we had no power for a week but the -40C is usually just in Jan-Feb.

Toronto is the same latitude as Cannes in southern France.

Sure, it's colder because of wind and ocean patterns, but it's not exactly the ultimate argument in "I know what it's like to live in a cold climate".

Cannes weather is more like Vancouver. Toronto might not be as Cold as Winnipeg, Edmonton, or Montreal but it's in Canada. Other than if they lived in Vancouver, to say someone who lives in Canada doesn't know what it's like to live in a cold climate is strange.

This article on Covid in Africa supports your theory / case.


Do you live in a non tropical region?

I live in Seattle. It's 12C in my apartment right now, I have the windows open and I'm certainly not wearing any gloves. Hell, I'm not even wearing any socks. I'm wearing long pants and a thickish shirt with long sleeves, and I feel totally toasty.

West coast of North America is less humid than many other places, and hence 12C in Seattle is not 12C in the Midwest or East coast. Less humidity means less heat transfer, and so 12C in Seattle can feel like 17C in NYC. And 12C in NYC can feel like 6C in Seattle.

Next holiday try Shanghai in winter.

This agrees with my intuitive impression of everything I've read on Covid-19: that the primary transmission vector is through the being in unventilated or poorly ventilated enclosed spaces with an infected person for ~15 minutes or longer.

I definitely feel like neither governmental policies or people's individual precautions and behaviours quite reflect that reality.

I'm a teacher at a school.

- We eat outside.

- We have filters upgraded to MERV-13 and the fans run the entire school day.

- We have windows and doors open on all classrooms, except for A) a few that don't open outside, or B) when it's rainy/windy to the point it's not possible. We have small, secondary HEPA filters that we run in those circumstances. (Often, we're blaring AC or heat into a room with all doors and windows open just to get a few degrees closer to comfort).

- We mask indoors, too.

So far, no secondary cases attributable to spread at school. We've had frequent testing for much of the time, too, so they'd likely get detected. Now a lot of the student body is vaccinated, too, but this dates to before that.

To add to that - younger children are really good with mask wearing in my experience - which is a big factor compared to the teenagers who ditch the mask as soon as no authority figure is in sight...or the adults with the maturity level of teenagers.

Does weaing a mask so often have downsides?

I'm not "anti-mask". I'm just wondering whether we will see studies in 10-20 years about a bunch of children with lung problems from restricted airflow or weird fibers or chemicals, or other pathogens that grew on the masks, or something we haven't thought of yet.

Or who knows? Maybe kids will all have super strong lungs. Or maybe lucky ones will have stronger lungs and others will suffer. I just don't know.

Anyone studying this (potential) issue?

Who knows. But we do have large parts of the world where wearing masks during cold season is normalized, without any massive evidence of adverse effect.

Having an entire population hiding their face on a routine basis when interacting with the public is an enormous downside. Completely unacceptable, and forcing it on the _entire_ population is downright evil.

Like the surgeons who have been dropping like flies for the past 100 years because they wear masks all day at work?

You could at least make an attempt to consider differences amd whether those differences might matter.

* Adult vs child

* Material (e.g. cotton)

* Quality

* Wash / replacement schedule

* Activities performed

And while you're at it, consider that kids aren't dropping like flies from covid, either. So if you're performing a cost / benefit analysis, the cost to kids wearing masks doesn't need to be very high before it gets higher than whatever benefit the masks offer.

> So if you're performing a cost / benefit analysis, the cost to kids wearing masks doesn't need to be very high before it gets higher than whatever benefit the masks offer.

Outright death is rare, but there's quite a few pediatric hospitalizations. They likely come with long term consequences, too.

For that matter, influenza has been greatly reduced, and there's a lot of chronic sequelae to influenza infection in youth.

And don't forget to add secondary consequences. I'm still willing to teach them in part because of reduced risk to me and my father thanks to masking. And a slightly reduced chance of killing a parent or grandparent by bringing home COVID is notable, too.

They get new masks every few hours. Or they did before the pandemic anyway.

That depends on how long they are in surgery, I'd think. And isn't the reason for switching masks not because of adverse affects to the surgeon, but to protect the patient? We have similar things with rubber gloves: You don't need to change gloves so often if you are, say, cleaning.

We had a scare like this here in Québec during April: https://montreal.ctvnews.ca/recalled-masks-were-worn-by-thou...

As far as I know, it was more of a fear than anything else. But it raises an important question: who controls the quality of the masks we wear? What's to stop a store from ordering substandard products and ordering all its employees to wear them?

The only issue I have seen so far is that constantly exhaling onto your eyes dries them out and can make them more prone to minor infections. Happened to me, doctor told me to not use contacts for a bit and take mask breaks once in a while. Outside of that, medical professionals wear masks all the time. Nurses are often subjects of medical studies because they are an accessible caprice audience. I know of no known cases of mask wearing being a bad thing.

Consider getting a mask that seals over the bridge over the nose. Bonus: this will also be much more effective at protecting you.

hmmm... thanks for that anecdote. i have been having dry eyes since last year... i thought it was age. But maybe I should try taking breaks when wearing masks.

Artificial tears are of great help as well.

I think the environmental damage is going to be a big issue in the near future, those hundreds of millions of plastic masks getting thrown away every day don't just dissolve into the aether; they stay around where they will pollute the environment especially the oceans. As far as I'm aware this topic hasn't been discussed at all by my government let alone a plan put in place to mitigate this environmental harm.

My kid's school doesn't have windows that open. It's too new for that.

Your kids school should have a good HVAC then which should run 24x7 and will have a fresh air intake which does the required number of air exchanges per hour. Add in some local air cleaners too.

Our newer buildings don't have windows that open and have interior hallways, so some rooms don't have doors to outside. They have better building ventilation and per-room standalone air filters, though.

Even just a single door open makes a big difference, IMO.

I've never attended a school that had doors to the outside from the classroom, honestly. Most, but not all, had windows that open, though.

The difference between temperate California (why bother with the expense of indoor hallway space?) and places where it snows. :D

Is that really a newer thing?

My ancient high school had 45-degree windows (for theft and suicide prevention I imagine). Why lock it all down? Cost?

It's a LEED rating thing.

If you can rely upon windows entirely for ventilation and thermal control, that's great.

Otherwise, windows that open leak more air when you don't want them to. They also let in more humid air, which in turn has a higher specific heat capacity and requires more energy to dry the air later. Their usage tends to be uneven, so you often have open windows while AC is also running elsewhere or in the same room, and this can upset air handling.

So, windows that open can paradoxically increase energy consumption in larger buildings.

More humid air with higher specific heat capacity: I’d expect the difference to be utterly negligible. Even at 40°C, the isobaric heat capacity of saturated air is only about 5% higher than that of perfectly dry air (~1.05 J/g·K, compared to ~1), and your slightly leaky window is hardly going to be resaturating the entire room.

As for the energy to dry the air, I’m inexpert in this area¹ but under the impression dehumidification is essentially just a byproduct of how compressors work (the evaporator’s low temperature causes water vapour to condense) rather than something that takes deliberate effort—that, if anything, air conditioners are commonly now deliberately revapourising water to avoid dehumidification beyond the desired level.


¹ But I am trying to learn for part of a project of my own, a velomobile and trailer to be able to live out of indefinitely, where in the ideal case that I haven’t determined is feasible I’d really like it if I could have one compressor to drive food refrigeration, cabin cooling, heating a low-temperature slow-cooker-style oven, and providing my water supply.

> More humid air with higher specific heat capacity

OK, so I should add a little more nuance:

* With more water vapor in the air, the air has a little more heat capacity

* With more water vapor in the air, the temperature band for comfort is a little narrower

* With more water vapor in the air, air conditioners need to work extra hard to provide the same cooling.

That is, the more water there is in the air to begin with, the more will condense and return its heat of vaporization to the room.

Certainly the comfort band is the key to it. Everything else is rounding error under even the most pessimistic estimates.

On phase change energies: I don’t know enough to quantify things definitely there, but https://en.wikipedia.org/wiki/Latent_heat#Specific_latent_he... looks like the right thing, and suggests around 2.4kJ/g, which with water being as much as 5% of the air (100% humidity at 40°C) would be as much as cooling the air down by about another 0.12°C for removing all of it.

Each of the terms is a small single digit percentage, but they multiply together to become a small but noticeable effect on building efficiency.

Each of the terms are single digit percentages if you were completely replacing cool, implausibly bone-dry air with implausibly hot and saturated air. With more realistic ambient and goal saturation, temperature and leakage figures, I think you’re looking at more like single digit hundred thousandths or millionths for most of the terms.

I disagree, and you can take it up with the people codifying energy efficient building standards and working on compliance with them if you care. :P

We have a local school being built. This was the argument for no operable windows.

Except … a pandemic! We are optimizing for the wrong thing IMO at the expense of simple practical, human driven comfort. Same reason we don’t have windows on the local trains anymore.

Practically for people in classrooms at random times, being able to open a window should be an option. Only central control of when the ventilation / heat is on just fails in so many situations.

It's an interesting tradeoff.

I like having windows that will open in my classroom. But in the larger buildings with central, indoor hallways, the benefit of windows is smaller (much less outer surface area vs. volume of space) and the potential costs are higher.

Aside from pandemic-proofing, the main benefit I get is from having more ventilation when I do things that don't need to be under a hood, but still produce fumes/smoke. E.g. soldering.

If it's still being built then it likely won't start being used until sometime next year and at that point we're back to optimizing for energy usage. It's best to pick a long term metric over a short term win when dealing with a building that will last for decades.

This presumes no further epidemics / pandemics, and discounts benefits to "normal" cold and flu season.

Do you think in normal years we'll still keep classroom windows open in the middle of flu season? Even in temperate California, the costs to classroom comfort and running HVAC to try and overcome outdoor temperatures is ridiculous.

Good modern buildings are being built with more ventilation and heat recovery built in. Taking this over windows that open can be a reasonable trade. Yes, on the pandemic axis, many of these buildings may be a little worse than a classroom with a whole long wall of opening windows.

I don't know, though I'd suspect that plans for increased air exchange are being considered. For much of the state, through much of the year, open windows are a reasonably minor consideration. Heat-recovery air-exchange would be more efficient, and again, though I don't know what's being considered, I'd suspect that this is part of current discussions.

The chief challenge is that of retrofits vs. new construction. Much of California's school infrastructure is 50--100 years old.

> I don't know, though I'd suspect that plans for increased air exchange are being considered.

In general, newer buildings with sealed windows have pretty good air exchange (with heat recovery) and filtration.

> For much of the state, through much of the year, open windows are a reasonably minor consideration.

Yah, tell that to me languishing masked a 95 degree classroom between building heat gain and a temperature in the 90s, and now ending up with a 60 degree room. It's workable, but it sucks, and we're wasting a lot of energy just to maintain a few degree delta T from outside with open windows. We've had a few weeks where the open windows have been great, but a lot more crummy weeks.

I'm a little jealous of those upstairs in the high school building that don't need to open windows.... and have nice temperatures in their classrooms... and have also had 0 secondary COVID cases. It's also really hard to conduct class when there's music, PE, etc, activities outside.

> The chief challenge is that of retrofits vs. new construction.

I thought we were talking in the context of a new school building being built without windows that open.

That said, windows are nice. If you have a class full of kids that are restless, sometimes opening windows and getting some outside noise or a breeze through the room changes the entire mood. It would be sad to lose that.

Much depends on just how open those windows are. "All windows wide open in every classroom" during very warm or very cold weather is excessive. A window cracked open for ventilation, and either at the top of the classroom (warm weather w/ cooling active) or bottom (with heating), and a fan within the room for vertical mixing ... might help.

(Keep in mind that mixing air also mixes infectious particles.)

A slight improvement is to have a single exit point (vented with a fan) and rely on structure permiability to introduce fresh air. That's effectively a negative-pressure system.

From there, exhaust and intake with heat recovery is the next obvious step.

I mention older construction as replacing building stock is a long-term and expensive process. New construction will account for an exceedingly small percentage of all utilised buildings. New construction currently planned or in process should if at all possible incorporate lessons from the COVID-19 pandemic, but that's a drop in the bucket. Retrofits are highly likely.

If you want to read further, I'm finding numerous results for a search on school ventilation in new construction and retrofits:


Among the first of those, from the CDC:

Reoccupying a building during the COVID-19 pandemic should not, in most cases, require new building ventilation systems. However, ventilation system upgrades or improvements can increase the delivery of clean air and dilute potential contaminants. Consult experienced heating, ventilation, and air conditioning (HVAC) professionals when considering changes to HVAC systems and equipment. Buildings that provided healthy, code-compliant indoor air quality prior to the pandemic can be improved for pandemic occupancy using less costly interventions. Below is a list of ventilation interventions that can help reduce the concentration of virus particles in the air. They represent a list of “tools in the mitigation toolbox,” each of which can contribute towards a reduction in risk. Implementing multiple tools at the same time is consistent with CDC’s layered approach and will increase overall effectiveness of ventilation interventions. These ventilation interventions can reduce the risk of exposure to the virus and reduce the spread of disease, but they will not eliminate risk completely.


Open windows and doors, when weather conditions allow, to increase outdoor air flow. Do not open windows and doors if doing so poses a safety or health risk (e.g., risk of falling, triggering asthma symptoms) to occupants in the building. Even a slightly open window can introduce beneficial outdoor air.


That cites an industry study by ASHRAE (professional association):


It also recommends on exhaust fans rather than interior circulation fans to minimise strong internal air currents, with intake provide as I've indicated above.

> Much depends on just how open those windows are. "All windows wide open in every classroom" during very warm or very cold weather is excessive

During a pandemic, it makes a lot of sense-- at least for the "extremes" of weather faced here.

> A window cracked open for ventilation, and either at the top of the classroom (warm weather w/ cooling active) or bottom (with heating), and a fan within the room for vertical mixing ... might help.

Might, but who knows how much? How does one weight the ordinary risk of sickness and infection (outside of a pandemic) with energy costs? (Especially when there are less energy-intensive ways to get the ventilation).

> A slight improvement is to have a single exit point (vented with a fan) and rely on structure permiability to introduce fresh air. That's effectively a negative-pressure system.

> From there, exhaust and intake with heat recovery is the next obvious step.

Yes, and pretty quickly from here you're ending up designing a structure without windows that open, so you can ensure that your fancy ventilation system does the right thing, filters don't get fouled, and you're not wasting heat.

> I mention older construction as replacing building stock is a long-term and expensive process.

Well, sure. But we were talking about it in the context of someone complaining a new building doesn't have windows. Older, smaller, poorly sealed buildings are a lot less likely to be retrofitted with no windows than new construction.

> It also recommends on exhaust fans rather than interior circulation fans to minimise strong internal air currents, with intake provide as I've indicated above.

Well, duh.

An otherwise well-sealed building, with a porous wall structure held at a small negative prssure, is effectively a very simple heat recovery ventilation system, too.

When I worked in an office, they had all of the windows screwed in to prevent opening to comply with new building codes. I imagine for suicide and accident prevention. It looks like these days you can only have windows that wind out a little. My apartment has these, but it also has an option on the AC controls to bring outside air in which can force ventilation if it isn't windy outside.

This is mostly for tall buildings though. For a school, it could be that they want to be able to control the airflow and AC. Having a window open could be letting out the heat causing the heating to work harder for no reason.

There's a tool for that: a brick.

True. All windows open. Some are harder to close back up than others.

Defenestration of covid

I’m very concerned that the mask debate for elementary school (and especially pre-school) is not considering the potential long term negative effects. The anti-mask side uses false arguments about breathing too much CO2. And the pro-mask side uses irrelevant arguments about how plenty of adults wear masks all day with no harmful effects (nurses/doctors).

But we’re talking about young kids here. Pre-school (age 2 - 4) is an especially critical time and early elementary is important too. This time is a short window in brain development when the brain is super elastic and learns many things. Much of language development isn’t just hearing and speaking, it’s also seeing the mouth movements. And this is the age when the brain learns how to recognize and display facial emotions. Is it possible by masking so much these young kids, we’re doing major damage to this learning process?

Maybe the answer is yes, or maybe it’s no. But no one is even considering this question. It’s just endless stupid debates about masking that doesn’t at all consider the special circumstances of this critical time in life, this short window when so much happens.

> But we’re talking about young kids here. Pre-school (age 2 - 4) is an especially critical time and early elementary is important too. This time is a short window in brain development when the brain is super elastic and learns many things. Much of language development isn’t just hearing and speaking, it’s also seeing the mouth movements. And this is the age when the brain learns how to recognize and display facial emotions. Is it possible by masking so much these young kids, we’re doing major damage to this learning process?

Maybe. But, on the flipside:

* We spend a lot of time outside and unmasked

* Many teachers use clear masks during phonics instruction and other critical times

* Wearing masks makes parents more comfortable with sending their kids to school, and so is enabling more social contact.

There are also some ancillary / random benefits, too. A big fraction of kids spend a big fraction of time up to age 7 fairly hearing impaired from low grade ear infections and congestion, and we're finally getting classroom audio amplification out at scale, adding a few decibels to teacher voices that will be helpful in the long term.

Also one more random note: emphasizing looking at the mouth so much for emotional reading is a mostly Western thing and not universal in human cultures. I'm guessing we end up with a generation of kids that read the eyes much more.

Great. We acknowledge the importance of this developmental period. So what are the options, and which option contains a downside that is more palatable than the others?

I.e. we fear the effects of total isolation of a four year old more than the risk of their stunted facial recognition practice etc etc

The risk of them getting sick is not significant. People are using their trumped up unjustified fears the media and government have whipped into them into demanding _some_ form of child abuse. The only thing they're willing to question is "which form?"

Significant hyperbole.

Elementary kids do not care one bit about wearing masks indoors. They picked up the habit quickly, don't complain, and now put the rest of us to shame. Indeed, they often don't bother (not out of fear, but just forgetting or not bothering) to remove when going outside.

And, the risk is much more significant than you imply, and the risk to us who work with them is substantial.

I'm looking forward to masks going away eventually for a lot of reasons (though I kinda hope they become normal for e.g. the worst month of flu season, like in many other parts of the world), but calling it abuse is just ridiculous.

> Elementary kids do not care one bit about wearing masks indoors.

Well I believe the opposite, and from having a teacher in the family I can tell you masks are INCREDIBLY detrimental to the educational experience. We're harming our children's education immensity by clinging to them.

> , the risk is much more significant than you imply

No it is not. It's not even a large enough risks in adults for the removals of freedom to have been justified, and there's MUCH, MUCH less in kids. The risk is virtually non-existent, not a worry whatsoever.

If you're still sitting here in 2021 and pushing for the continual suspension of freedom "for the children" over a near nonexistent worry, you are part of the problem.

> and from having a teacher in the family I can tell you masks are INCREDIBLY detrimental to the educational experience.

OK. I'm teaching and doing fine. So are my colleagues.

Well they were hugely detrimental to all the teachers I know. So either you're downplaying the impact or ignoring it.

That's awesome but why isn't it universal?

In some places it's far too hot or cold most of the school year? Or inclement weather is common. Or students have severe alergies. Or there isn't enough space for school buildings to be designed that way. Or the local air/noise pollution is too great.

It seems to me like the ability to design a school like this would be the exception, not the rule.

So let me ask you: with such well-ventilated facilities, what is the marginal benefit of masking? And is this benefit worth the difficult-to-quantify but very real cost of students being unable to see the faces of their classmates?

> So let me ask you: with such well-ventilated facilities, what is the marginal benefit of masking?

It's difficult to estimate. Of course, even with all this care, not everywhere is equally well ventilated. My room is wide open to the outside, but there are other rooms depending on central air and the room filter which may not be as well off. Trying to form policy on a room by room basis would be nutty.

> And is this benefit worth the difficult-to-quantify but very real cost of students being unable to see the faces of their classmates?

We do go outside quite a bit, and most students choose to not mask outside and thus see their classmates then. There's also the very real benefit of making many students-- and me, their teacher-- feel safer.

IMO the biggest cost is it's slightly harder to understand each other and we have a few more misunderstandings per day.

yikes, you think "feeling" safer is an adequate reason to mask?

Yes, I do. My dad has SLL, with a ridiculous risk of mortality should he be exposed. Yes, he's fully vaccinated, but the amount of protection he can expect from the vaccine is dubious.

Further bounding the risk of me getting exposed by a student (ventilation + masking) lets me both see my elderly father and continue to teach. I don't financially need to teach, and as much as I find it rewarding, I'm not willing to take a large risk of killing family members to do it.

> And is this benefit worth the difficult-to-quantify but very real cost of students being unable to see the faces of their classmates?

I would figure the first thing needed to answer that question is defining the "difficult-to-quantify" cost, right?

There is no real benefit to masks for many countries with high degree of vaccination.

The hospitalizations tell the story, ie. we are doing better than under the big flu seasons from the past.

It's more that the majority thinks that masks work, so it won't change anytime soon.

This matches the policy at my children's school - and thankfully the outcome has been the same as well, with no community spread. These seem like reasonable and effective precautions to me.

A potentially fantastic outcome from all this is that many more public and private spaces will be designed and retrofitted with very good ventilation.

Beyond curbing the spread of natural airborne diseases, it also may decrease the attack vector in our societies for airborne bio-terrorism/warfare.

And even beyond all that, we're becoming increasingly aware of how important clean air is for our overall health even without the risk of pathogens.

I hope that's true. My experience so far has been pretty minor symbolic changes though. My employer sent emails about how they swapped their MERV filters for slightly better ones, and something hand-wavy about adjusting the external air percentage "when feasible" (with no numbers). I would be surprised if they do major retrofits, like a new heat exchange system allowing significantly higher percentage of outside air, at least as things currently stand.

I could see it happening in new buildings, though. Possibly in existing buildings if an easy-to-read summary number for ventilation became popular and the numbers for specific spaces became easy to find and widely publicized. Then companies might be willing to pay more to rent space with a higher "ventilation score", especially if employees balked at working in spaces with low scores.

It will eventually become just another element in economic selection.

The wealthy and the high income earners will start avoiding buildings, businesses, and organizations that won't or can't sufficiently upgrade to be considered safe. Their money will flow and support the healthy/safe alternatives.

Those that are left behind will be the dregs that the poor and desperate use and will gradually fall into disrepair until their owners go bankrupt or give up and sell to someone who has the means and drive to upgrade or demolish and rebuild.

The same thing happens to any old infrastructure where people can vote with their feet.

It won't change my habits. I'm not going to ask every business owner to provide their facilities maintenance info before I go to a place of business. If I get sick I get sick. It may or may not be the fault of the business.

In the town where I live, office and apartment buildings are assigned letter codes based upon energy efficiency, which are then publicly displayed. It's not unfeasible to imagine that something like that could be done for the health and safety profile of buildings. Even if many people chose to ignore such information, I think enough would feel hesitant to enter a building with an "F" grade that it would end up having a positive effect overall.

What town/country?

I wonder if it just gets built into health/building codes. I don't want to ask every business to do X and yet I hope sometimes regulators do.

I think the challenge with indoor air circulation is the energy required to do so, especially when heating/cooling of the air is involved.

But, I'd sure love better indoor air quality.

Well, given that virus particles start to be meaningfully filtered only at a certain MERV level (14?), that upgrade may in fact have been more than a "minor symbolic" gesture.

MERV-13 is pretty good. Better than 90% filtration at 1 micrometer and up. It then comes down to how many air changes you can expect.

> Better than 90% filtration at 1 micrometer and up.

What means it's probably useless against any airbone virus. But it's pretty great against particle pollution, in case you want to use it in a private space.

Virus size is not the correct metric for a virus transmitted in aerosolized or droplet form (notably, COVID19). What matters is the aerosol/droplet size, which in this case is substantially above 1 micrometer.

Viruses don't circulate bare in the air. Droplets containing viruses do. It's thought that it's mostly carried within droplets that are 5um or larger.

Just in case smaller particles have a substantial role, I quoted the 1um number.

A couple years ago I bought a CO2 meter, and was astonished to see it going over 1000ppm in my office. Since then, I always keep the window cracked, keeping the CO2 levels usually under 500.

The meter was one of the best investments I ever made.

Yeah when our office got those meters it suddenly explained why I got pounding headaches after long days. I'm pretty sensitive to it apparently. I've seen it go as high as 1400 :(

Cognitive performance starts declining at 1000 ppm.

Makes me wonder if the atmospheric increase from ~280ppm to the current 420ppm over the past 200 years is having some minor, but statistically significant effect on our collective cognition.

If it is, it's probably far overwhelmed by the shear weight of more well educated people and better tools at our disposal.

I've done the same recently for my home. It's tough to keep good interior air in the winter when the building is not designed for it.

Ha, at the University where I work, they are "upgrading" the windows to more energy efficient (good) but they will no longer be able to open up to the outside. All of the occupants complained, but sorry too late to change the plans, even though we don't have a contractor picked yet. We also have a relatively mild climate where opening the windows 10 months out of the year would insure adequate cooling.

> it also may decrease the attack vector in our societies for airborne bio-terrorism/warfare

Sounds extremely far-fetched. Any terrorist attack will be designed with the countermeasures in mind. Deploying enough biological agent to swamp the ventilation system would likely not be an issue.

I'm pretty certain I worked in an open-floor plan office that had windows designed to "impede" small airplanes being flown into it.

I speculate this fact -after- a someone actually did fly their airplane into our building. The pilot received exceptionally bad customer service from us and was attempting to kill one of our leaders.

Lesson learned: Don't give bad customer service if you work in the World Trade Center.

There have been documented cases of infections happening in seconds.

Yes, longer exposure time increases infection probability, but the 15 min threshold is arbitrary, like the 2 meter social distancing.

A bit like the "you can pick up food from the floor if it sat there for less than 5 seconds" meme.

The "public" in public health refers to the fact that it's the aggregate health status of a population that matters.

Arbitrary guidelines are chosen:

- Because at the population level they're likely to be effective. Yes, individuals may get sick. Or die. But with the measures in place, overall risk and impacts should be reduced.

- They're actionable, memorable, and can be monitored and observed. Masking, hand-washing, limited exposures, limited occupancy, maintaining distance --- these all help reduce transmission, they're simple guidelines most people, even young children, should be able to comply with, and they can be readily and visibly observed.

It's a balance of benefits, risks, adoption, and enforcement.

Immunity status is harder to assure and measure, but vaccination standardises the innoculation, creates a memorialisable event, and can be checked if needed at specific locations and junctures.

The "five second rule" is far less meaningful than what's on the floor. But if you happen to see something fall, note that where it landed was reasonably clean, and if possible can wash it ... you're likely to make a better assessment than if it's been sitting for a few days. Even then, I'd make a sharp distinction between five seconds on my bedroom floor, vs. in the bath, or in a public building or street.

That said, much food comes from the ground. Wash and prepare suitably, you're reasonably safe.

By infection you mean people actually getting sick, or just dead virus DNA fragments detected in the nose with PCR?

How are infections measured in seconds?

Up until about 2 months ago contact tracing in Australia was very effective. Contact tracing teams were able to trace who and where each person got infected. They were also notifying/testing/isolating first and sometimes secondary downstream contacts (up to 400 people in the case of one country town outbreak).

One of the infections was traced to a department store and the interaction between the two people was caught on cctv. They walked past each other and didn't talk. It was seconds.

It’s not like you can see the viral particles jumping over in that exact moment. I’m sure there is more to the story, but let’s not try and claim that this is incontrovertible scientific proof that infection happens “in seconds”.


* A vast majority of infections can be traced

* You have an infection whose only traceable contact is for a few seconds in a store...

It seems pretty likely that the infection happened in the moments surrounding those few seconds. Especially when we have multiple circumstances like this. Especially when it agrees with our underlying understanding of the germ theory of disease.

Extended contact makes infection much more likely. But people who are sick shed live virus, and there's not a safe level of exposure of live virus where infection is impossible.

Not necessarily. I'd be interested to know if the virus samples from those two people were sequenced in order to prove transmission from one to the other. Absent that evidence there could be other explanations such as : transmission was from some third person not known to the contact tracers.

> transmission was from some third person not known to the contact tracers.

This becomes an unlikely explanation once

> > * A vast majority of infections can be traced


> > Especially when we have multiple circumstances like this.

The probability of an alternate explanation becomes exceptionally unlikely. It's further reduced by our general scientific understanding that:

> > But people who are sick shed live virus, and there's not a safe level of exposure of live virus where infection is impossible.

Infection from a momentary contact is fairly unlikely. But when you have a massive number of momentary contacts in the populace, it happening many times becomes a near certainty.

E.g., this:

> Several individuals in Australia were also infected with the Kappa variant through lingering virus aerosol particles in the hallway of a quarantine hotel in May. Though the individuals had no direct contact with each other they opened the doors to their hotel rooms within 30 minutes of each other and tested positive for the same strain.

No complete sequencing, but the same variant... spread several times apparently by the same mechanism of indirect contact, several individuals infected. In a quarantine hotel, where there's not many alternate explanations available.

Or this one, confirmed by sequencing:

> A similar event occurred earlier in April where two families quarantining in rooms next to one another were found to share the same viral sequence, after briefly opening their doors 30 minutes apart.


In Australia earlier this year when infections were happening the rate of single-digits per day, they could trace the source of an infection to a fleeting encounter of two people walking past each other in a shop.

Source: https://www.abc.net.au/news/2021-06-22/covid19-cctv-footage-...

I haven't followed Australia's progress with COVID-19, so I hope these questions aren't too obvious or bothersome:

Were these single-digit infections all symptomatic, or were they detecting asymptomatic infections too? What is the false positive and false negative rate of the type of testing Australia is doing, and how many people were being tested during this time?

If some of the infections were asymptomatic, is it possible that some of them are false positives, and the fleeting encounter was also a false positive (either a false positive test, or that wasn't the true source of the infection) just due to random chance?

I have not seen widespread data on symptomatic vs unsymptomatic cases however during the most recent NSW surge around 5-7% of new infections ended up presenting to hospital at some stage. Testing was widespread and likely highly compliant - daily testing stats were available, NSW at one point was having 180k tests per day (PCR). People were notified of sites of exposure (or via checkin apps) and asked to test. Given it was PCR, false positives were as you would expect quite low but there were at least 2-3 false positives I recall being discussed in the media.

In answer to your final question - no - they were PCR confirmed cases. There was also a high degree of sequencing occurring to enable clarity on lineage transmission

Positives would be re-tested to rule out false positives.

In that period 30k-60k people where being tested in NSW. https://www.covid19data.com.au/nsw

I think the person meant that it only took seconds of total contact time to cause an infection. Even if the infection took days to develop.

Annoyingly, my intuitive impression is that we are still far more ignorant than we'd care to admit. Being in a place where we all willingly wear masks to grocery shop, I get the impression we are far more cautious than most places. Still, I expect it is just a matter of time before we are exposed.

Why? I honestly don't know. It isn't lack of wanting to be safer. But it has gotten fatiguing to try to keep up with what makes us safer today. I remember the start when folks wiped down delivered groceries. Even isolated them for a few days. Nowadays, it seems masking is still the visible thing to do, but most seem pretty sure that it is the vaccination that will make a difference. Anything else is a slowdown, at best.

> I remember the start when folks wiped down delivered groceries. Even isolated them for a few days.

I still isolate groceries for at least 6 hours, delivered or not. Still clean my hands or wear a glove when I touch something outside.

I haven't got sick since Covid appeared. I used to have pretty severe nasal allergies (or so doctors told me) at least once a month, I haven't had one episode since early 2020. This is a life-changer for me.

Same thing for the usual minor health issues such as cold, cough, sore throat. All gone.

So I keep my Covid routine, probably even if Covid goes away, it's not that much of an effort and the results have been spectacular.

I can assume that if you are taking those measures, you also avoid crowds of any sort. Which probably does a lot of the heavy lifting for you.

For me, I also saw that we had fewer sicknesses when the kids were all home schooled. Not shocking, we got a ton of bugs when they started school back. Not sure how sustainable it is to have such isolated lives, though. :(

> I can assume that if you are taking those measures, you also avoid crowds of any sort.

Correct. Being a software developer helps immensely.

I do absolutely nothing, including not wearing a mask in an area that demands I wear one. Nor have I gotten any sort of shot.

The only thing I do is that I wash my hands every time I return from public, as I always have been. I haven't gotten sick either.

I have had the flu twice. The first was in college and then second was when my kids were in pre-school/elementary school.

I think you mean "I have had flu-related symptoms twice". Given that influenza is a virus with a huge number of variations, and almost nobody is ever tested for infection with any of them, there's every chance that you've had many more influenza infections, but no symptoms.

Nope these were confirmed cases.

Yes, I understand that the times you had symptoms, the infection was confirmed to be flu.

What wasn't tested (or detected) were the times when you were asymptommatic but still infected with one the many influenza variants.

English is a little problematic when it comes to describing infectious disease. In all cases, there is the disease agent (e.g. an influenza virus) and there are the disease symptoms (e.g. "flu"). But we tend to say "I had the flu" without it being clear if we mean "the disease agent was present" or "i had the symptoms".

Following your logic I should have had residual immunity to keep most of the variants in check. The first time I had the flu in college it was brutal and I was out of commission. The second time diagosed I got tamiflu after the flu test and it was mild. I also knew I was sick. Anything in between was unnoticed and I have had a flu shot since they first came on the market.

Not necessarily. The immunity fades with time, so it is possible that you could be infected again. The residual immunity might be strong enough to prevent symptoms however. Each such exposure can boost your immunity. Nevertheless, influenza virus has many mutations and sometimes can cause breakthrough disease even in vaccinated.

Many influenza infections are asymptomatic. Unless you've been getting tested every week, it's entirely possible that you have had the flu more than twice.

The precautions required to guarantee zero exposure to an airborne virus are incredibly more substantial than most of us will ever be able to carry out in ordinary life (think biohazard labs).

So yes, almost all of us are going to be exposed to SARS-COV-2 at some point. Slowdowns are doubleplus good because the biggest risk from the disease is related to its impact on public health care systems rather than serious illness or death at the individual level. Masks slow down transmission, vaccination reduces chance of required hospitalization.

Zero is ideal, but a reasonable reduction is acceptable if we can pile together a number of different mitigations to get the effective transmission rate below 1.

This angle feels like giving up on all of the covid deaths. And is somewhat at odds with all cause mortality being attributed to undiagnosed covid.

I am open to the argument. Just feels to be begging a lot of other questions.

I don't feel as if I'm arguing for "giving up on all the covid deaths". On the contrary in fact:

(1) likelihood of death decreases with the passing of time, because of improved treatment (and maybe testing also). So to minimize death, you want your exposure to be delayed as long as possible.

(2) there is reasonably convincing evidence that exposure level is significant in determining severity post-infection. Therefore you want to live within a community and with habits that keep you away from high exposure as much as possible.

So, the same strategies that slowdown exposure also help to reduce deaths

I guess you skirted closer to the flatten the curve argument than I was comfortable with. Seems that, in retro, it caused folks to take precautions to try and keep hospitals clear, and ultimately threw a lot of nursing homes under the bus.

That said, your first point is a good one. If made difficult by how many later waves in most places have similar death peaks to earlier ones.

I still think we are far away from really having evidence on any good strategy, sadly. All of the places that had it under control seem to have lost said control.

Which, ultimately, is a good enough argument for me, to not just give up on things that have any chance of helping. Sucks, as I am clearly open to the arguments that deniers use. Which... I'm not trying to further that angle, either.

Preventing exposure is impossible over the long term. Fortunately the vaccines and other treatments can prevent most deaths.


Highly improbable, but not impossible, particularly for beings with finite lifespans over the long term. Herd immunity is reached at HIT=1-1/R0, at which point the infection rate will slow, and some of the remaining uninfected and unvaccinated individuals will have avoided exposure, as the chain of transmission to them will be broken. Back at the start of COVID-19, that would have been a sizable percentage of the world, though now (due to the higher R0 for delta) it is a much smaller percentage of the population who can escape exposure in this way alone.

And note that R0 can be changed by altering some environmental factors in the formula above.

Viruses spread because of their hosts (us). In the past it was because of various sanitary conditions that allowed viruses to spread. Now that we have largely clean sanitation practices (showering, clean tap water, toilets), our practice of staying indoors and often in cramped places (elevators, transportation, work, school) is an easy way for a virus to chance on this way to spread.

Some patterns become more evident when viewed with the perspective of time.

There were numerous diseases that it's now clear probably had a very strong airborn-transmission component. Some we know of and their potential for transmission is extreme, e.g., smallpox. Turberculosis transmission all but certainly benefitted from cramped living, working, and travel conditions. Legionaire's disease was discovered in the 1970s, thriving in the cool, moist, air-conditioning ducts of a hotel (and affecting a convention of the American Legion, hence the name).

"Seasonal" cold and flu are also all but certaily amplified by indoor living, working, shopping, and related activities. The impact of COVID-19 countermeasures in reducing their prevalence over the past two years has been profound.

"Sick buildings" have been an issue since the 1970s (largely following increased energy-efficiency measures reducing air circulation), and there seem to be multiple components including chemicals in structural, decorative, and celaning/other materials. I predicted early into the Covid pandemic that changes to building construction, operations, and HVAC systems would likely be a lasting legacy of this pandemic.



Future people: “You mean they just dumped their used air and everybody else had to breathe it in?”

For better or worse, the medical community is usually hesitant to recommend things before studies have been done, and some "common sense" advice is difficult to test.

But some things have no potential for harm, and they should be recommended with higher priority than something that could be harmful at the same likelihood of efficacy. It seems to me that the recommendations are mostly based on how well it provides a predictable financial benefit to a specific investment (mail-order, pharma, etc).

They supported lockdown of the healthy when no major western country had it as a tool in their pandemic plan and specifically recommended against it.

Masks have been recommended heavily since the beginning without good evidence that they are effective. [0]


CONCLUSIONS Most included trials had poor design, reporting and sparse events. There was insufficient evidence to provide a recommendation on the use of facial barriers without other measures. We found insufficient evidence for a difference between surgical masks and N95 respirators and limited evidence to support effectiveness of quarantine. Based on observational evidence from the previous SARS epidemic included in the previous version of our Cochrane review we recommend the use of masks combined with other measures.

We've had a lot more information come out since March 2020.

The Bangladesh study is a particularly good one, demonstrating changes in disease prevalence even with less than half the population following masking recommendations: https://ncrc.jhsph.edu/research/the-impact-of-community-mask...

The bangladesh study showed that groups of people that are spending large portion of their days inside small huts will benefit from mask. One particular area was also mosques which has a large number of people coming and going, with people being near each other indoors.

Mask makes great sense in specific contexts. Near vulnerable groups. In tight spaces and areas of low ventilation. In areas where a large number of people meet. The further away from such areas, the less evidence we get.

There is a reason why conferences is generally associated with people getting sick, while the same can't be said about the beach.

Sure, skip the mask at the beach. We've known outdoors is likely quite safe due to ventilation for a long time now.

The Bangladesh study is likely informative in busy grocery stores, retail, offices, schools, etc.; certainly more than just "inside small huts".

> The Bangladesh study is likely informative in busy grocery stores, retail, offices, schools, etc.; certainly more than just "inside small huts".

The study did not show that. It was a study conducted in rural areas of Bangladesh, areas with small villages of huts and some mosque. Those are quite different from a large city mall and office complex. Schools are a even more complex since while children has a significant higher rate of getting sick in general, the transmission rate between children and adults is significant lower. The ruling on school lock downs and mask in schools has yet to be established.

We can look at specific examples. If you are on a packed plane then a mask is pretty good idea. Traveling on a bike then it is unlikely to do anything good. Mask in crowded open floor plan with bad ventilation, yes. Mask in personalized offices with good ventilation, no. A conferences, yes. A school, maybe. A bench, no. A large grocery store in off-hours, less likely. A crowded grocery store in rush hours, more likely. In a public bath house, the data seems to indicate no.

Things that seems to correlate with transmission rates seems to primarily be about: distance between people, ventilation and humidity, practicality of staying isolated at symptoms, age and risk groups. Raise any attribute of those to an extreme and one can get data that either prove or disprove masks as effective.

Weird to pick a release from March 30, 2020. A modern review[0] concludes:

Our review of the literature offers evidence in favor of widespread mask use as source control to reduce community transmission: Nonmedical masks use materials that obstruct particles of the necessary size; people are most infectious in the initial period postinfection, where it is common to have few or no symptoms (45, 46, 141); nonmedical masks have been effective in reducing transmission of respiratory viruses; and places and time periods where mask usage is required or widespread have shown substantially lower community transmission.

The available evidence suggests that near-universal adoption of nonmedical masks when out in public, in combination with complementary public health measures, could successfully reduce Re to below 1, thereby reducing community spread if such measures are sustained.

[0]: https://www.pnas.org/content/118/4/e2014564118

This paper’s from March, 2020?

Note that I said "since the beginning".

Which is also incorrect; the US Surgeon General tweeted masks "are NOT effective in preventing general public from catching #Coronavirus" in Feb 2020, and Fauci said "There’s no reason to be walking around with a mask" in Mar 2020. Recommendations were frequently firmly against masking early on.

And the fact that that was 1) motivated by other concerns (principally: ensuring availability of then VERY scarce masks for medical personnel and first responders), 2) bad advice, and 3) backfired very badly has been public record since ... March of 2020. See Zynep Tufekci's "Why Telling People They Don’t Need Masks Backfired"

Given that there is indeed a mask shortage and that medical workers absolutely do need these masks more, what should the authorities have said? The full painful truth. Despite warnings from experts for decades, especially after the near miss of SARS, we still weren’t prepared for this pandemic, and we did not ramp up domestic production when we could, and now there’s a mask shortage — and that’s disastrous because our front line health care workers deserve the best protection. Besides, if they fall ill, we will all be doomed.

If anything, a call for people who hoarded masks to donate some of them to their local medical workers would probably work better than telling people that they don’t need them or that they won’t manage to make them work. “Look, more masks would be great. We are doing our best to ramp up production. Till then, if our medical workers fall ill, we will all be worse off. Please donate any excess — maybe more than two weeks’ worth per person — to your hospital” sounds corny, but it’s the truth.


Oddly, it seems to be those who still most strongly resist wearing (or bully others for wearing) masks who seem to recall those first few weeks of ill-advised messaging.

I got COVID when I was in jail. There is almost no air circulation in some jails, and a lot, like the ones I was in, are hermetically-sealed boxes. 40 people stood in a box the size of your living room. Breathe that COVID in, baby.

Getting vaccinated, staying isolated if you are infected, and wearing a mask all work related to that

Medical policy always seems to float around various ideas before they really grab hold. It maybe shouldn't but it takes time it seems.

A metaphor I was thinking of earlier.

If a guy is going to piss on you, you're going to be happy if he has to keep a pair of speedos on as he attempts it. You could also just move further away from him.

But if you're both swimming in the same pool while he pisses in it, those speedos will make little difference anymore. Neither will your distance from him help very much.

What will help much more is the amount of water in the pool, and the amount of fresh water being pumped in and old water pumped out.

Sometimes metaphors are less than helpful. This is one.

> Neither will your distance from him help very much.

The amount of piss distributed is still determined by volume, so more distance => weaker concentration, which... helps a lot?

only in the transient stage. in the "steady state", it distributes evenly to the entire pool, and the only thing that matters is total volume (+ intake, - outlet), distance irrelevant.

True assuming good mixing (big assumption), but why are you conveniently throwing out concentration?

Are you assuming that if "any part of the piss touches me, regardless of how much - i die."?

edit: sorry thought you were grandparent poster and was a little more aggressive. But still..

You'd have to use a very special Speedo in this example, though. One that filters microparticles out of the urine, keeping large parts the grossness inside.

Also, don't touch the outside!

not a great metaphor imo. gives the impression masks and distance do nothing, and we know they do

To this day, there is no mandate whatsoever in any public transport to keep windows open. NiH? CDC? Missing in action thanks a lot.

Uber could simply ask customers to always ask for windows down.

This to me is the biggest unsung crime of the pandemic by govt officials and private industry alike.

Uber and Lyft in fact require customers to agree to keep windows open “when possible” in the same pop up as reminding them to wear masks. Short of intrusive integrations with some hypothetical car window status sensors, not presently deployed in the fleet, that’s getting close to the limits of what can be effectively achieved for now.

And they require the driver to have recirculate off, fresh intake on.

In Tokyo most train companies agreed to keep the windows open at all times and encourage passengers to lower the windows if they see a closed one. Cooperation is very high and I only see them closed when it rains.

I used to prefer Uber/Ola over the humble auto rickshaw [1] mainly because of two reasons: cars are safer; and an air-conditioned car helps avoid pollution from traffic (which is quite high in Bangalore). Now I prefer auto rickshaws (at least for short distances) because they are well ventilated due to its door-less design. The back seat of an auto rickshaw is constantly braving the elements (sunlight, dust and wind) and is likely to be more germ free in this context. To make it even better, now these autos have a transparent plastic screen between the driver and riders, thereby isolating them from each other while being open to the environment.

[1] https://en.wikipedia.org/wiki/Auto_rickshaw

I'm fully vaccinated and also got mild COVID once, so as someone in my 20s with no underlying health conditions, I don't really care about ventilation anymore.

Right now, the temperature is -9C/16F. Winter is really just starting, and it'll probably get colder. It isn't snowing right now.

I'm not convinced windows being down is going to do anything outside of making folks cold. Air circulation happens still because cars have heating systems that draw air in from the outside.

And fwiw, the busses here do not have windows that open (outside of emergency panels). I'm in Norway, though, and folks were pretty decent at keeping distance even before the pandemic.

Good ventilation is easy to do in the summer months, but it is winter in the northern hemisphere at the moment, and fuel prices are at all time highs. That means adequate ventilation is likely an expensive thing to achieve. Not to mention the environmental consequences of extra energy consumption, along with the plastic pollution from littered masks and lateral flow tests - they’re absolutely everywhere.

I'm sorry but this is unacceptable.

We have shut down entire industries, made some people 2nd class citizens, and wrote blank checks to healthcare companies to solve this problem,

and your concern is lost heat and the environment ?

Any common sense government would have mandated open windows a long time ago, in most transportation systems and in federal buildings that could bear it, instead we wasted valuable time with politics

I’m not sure what there is to accept? I never said it wasn’t worth it, just that there are financial and environmental costs to consider. Where I live heating a building is expensive and many people can not afford to do it adequately at the best of times.

What's the end-game there? Opening windows doesn't eradicate the virus. Admittedly, we don't have a clear end-game as things stand, but what you suggest is just another mitigation factor, not a solution.

Why wouldn't we want to maximize mitigation? Especially something so simple and eady to do?

It seems we put ALL our "money" on a vax and that isn't panning out well. So now we have lost time, nudged behavior in conflicting directions, and so on. We just keep doubling down on a mindset that is clearly flawed.

The end game is that we get to all enjoy some fresh air, isn't that enough? I've been doing this for years, long before any covid.

Well if we can eventually drop the masks. Otherwise the air is still hot, humid and stale. I personally have anxieties due to them (related to an almost-suffocating experience in the past). But I know many people suffer with them for different reasons.

I know we need the masks now but it shouldn't be a permanent solution. It's very invasive. For 30m on the metro perhaps but not all day at work, school... If covid isn't doing away there must be a better way to reduce levels enough. After all it's only a mitigating measure, not a 100% preventative one.

I air my house every day too. Because I love the fresh air.

I hope that in the mean time we'll get powered masks though that don't have all these drawbacks. Especially for people like me with medical issues. Razer has one already but it's impossible to get (I've tried getting one on the last drops and they sell out before my order page loads) and it looks too much like a massive gas mask IMO. It's not suitable for a lot of situations. Still, I'd get one if I could :'(

Where do you live?

Seattle. Before then, New York.

Common sense would have also dictacted we were more prepared - after a warning pandemic less than 10 yrs ago - we were not. The idea of a pandemic is so cliche that Hollywood has made multiple bad movies about one. But we weren't prepared (e.g., masks and PPE)?

Common sense (in the USA) would have dictated the extended care facilities were better protected early on, yet they were not.

There have been so many gaffes and bumbles that it consistently boils down to: it's either negligence or it's intentional. Neither is a good answer.

Any common sense organization would be strongly suggesting that people wear N95 masks with vents (more comfortable) to protect themselves. But here we are - still wearing whatever we can find around the house.

No, you shut down entire industries not because of poor vents in a concert, but because some overly powerful, yet replaceable and hysterical bureaucrats decided to cover their asses (from being eaten by the exact same bureaucrats) with arbitrary loud and visible policies that had little correlation with actually solving any problems.

Notice similarity between places like Florida (less power-hungry governments + freedom-loving population) and places like Belarus and Russia (more authoritarian central gov that does not fear for losing its seat in the next election): both were shutting down things to a much lesser degree than everyone else. I think the reason is exactly the combo of "I can have arbitrary power as long as I have good PR" in the average democratic political environment.

heat recovery ventilators are a thing, but not nearly as popular as they should be

They already solved this in NYC and Chicago with extra hot radiators by windows.


The “spent breath” of the occupants of poorly ventilated homes contributed to 40% of the deaths in the country, he claimed, and often said “man’s own breath is his greatest enemy.” He would spend decades promoting the cause, designing ventilation schemes for buildings, penning a 1869 book, Leeds on Ventilation, and lecturing across the country. He explained his ideas with the aid of a “magic lantern” projector — think old-timey Powerpoint presentations. He’d show slides of a family in their drawing room, then add a slide showing red air coming out of the father’s mouth. The child crawling on the floor would eventually fall over. It “scared people to death,” Holohan says.


There is also a problem of comfortable humidity levels. If you just have open windows, it seems like you will have very dry air.

There are modern solutions for air exchanges that do retain some of the heat and moisture while allowing for fresh air to ventilate the indoor space.


Dry air is a problem with any heating, but for those who are interested in a solution that currently exists (it’s a bit wasteful), is curious why they get too hot, or wants an easy solution without a new HVAC installation it’s very simple.

Our radiator had a pan for water over the heater to keep humidity comfortable we’d refill.


If your windows are open you will trend toward outside weather. If you’re in a dry climate then yeah it’ll be dryer but the reverse is also true. Outside air is far better than inside nearly everywhere in the world

Cold air can hold a lot less water vapor than warm air. If you open the window when it's cold outside, then the air will become very dry as it heats up.

So even if you have 80% humidity outside on a cold winters day, once that air gets inside and heats up to room temperature it's going to be like 20% humidity.

Indeed, even in San Francisco I measured indoor humidity as low as 18% before I got a humidifier, and dryer+colder places (e.g. Salt Lake City) could be even lower inside. Humidity below 40-50% at indoor temperatures has noticeable negative effects for me.

As other comments have mentioned, in the long run for maximum health and maximum energy efficiency we really need to design our buildings to be air tight, with energy-recovering ventilation systems and humidity control.

That happens even if you don't open your windows, since buildings aren't perfectly sealed.

It also depends greatly on how well your structure is insulated and where (or whether) vapour barriers exist.

Vapour condenses against cold surfaces. This is why in winter poorly-glazed (e.g., single-glazed) windows "steam" up (really: condense), or frost over. Similarly water will condense against exterior walls, and may lead to degraded sheetrock (newer construction) or plaster (in older buildings), or rot. Where walls are insulated, a vapour barrier _before_ the insulation can lead to condensation inside the wall, again, against the exterior (cold) surface. The result is that even if the interior is humidified, moisture is "sucked out" by the exterior cold. (More accurately: vapour condenses against cold surfaces.)

In summer, the problem is reversed, with warm humid exterior air condensing on surfaces cooled by interior air conditioning --- the outside of windows, or again, inside walls. Interiors can see higher relative humidity than the outside, and dehumidifiers may be needed.

For humidity, the key issue is that relative humidity matters for us and that is temperature dependent.

For example, if outside air has 100% humidity, then it effectively can't absorb more (e.g. evaporation of sweat) and would make things moist, but at -5 degrees Celsius, which I have now outside my window, that's only 2.46 g of water per kg of air - and if that exact air flows inside and gets heated to room temperature then it would suddenly have only ~17% humidity and would gladly absorb moisture from wherever possible e.g. my throat or skin; and any air going outside would remove more water vapor than the incoming air can possibly replace.

There are ways around that (ventilation systems that exchange temperature and also retain moisture), but they need to be installed at some expense, you won't get that by opening a window.

I appreciate your detailed rundown. This kind of stuff is not intuitive to me.

Reminds me of The Lost Art of Steam Heating by Dan Holohan: https://www.youtube.com/watch?v=TQB0KK2rxcw

Excellent video and information, as well as a rabbit hole to dive into (Holohan's work).


It baffles me that Fauci etc didn't mention this in the next breath after hand washing and masking. It's easy during nice weather.

Is hand washing even that relevant given the virus gets mostly inhaled? I've never seen any studies on this.

As I understand, hand washing isn't as important as they thought it was at the beginning. They thought it transmitted by touch more than it does.

I haven't seen any proof either. But people keep poisoning their lungs with alcohol and other toxic vapors!

To be clear, I'm very much in favor of hand washing and have been using hand sanitizer whenever I come home since we'll before the pandemic. It helps with other infectious diseases, but I wonder about COVID

Washing your hands properly with soap and water is much more effective than hand sanitiser in typical use. Hand sanitiser is most useful when you don't have convenient access to soap and hot water. Since you're arriving home anyway, you might as well wash your hands properly — the skin on your hands will thank you for one less exposure to hand sanitiser, too.

Hand sanitizer is more effective than your average person's hand washing practices, which is pretty poor

That statement could only be true if you are comparing perfect-use hand sanitiser to typical-use hand washing, which isn't reasonable. If someone can't wash their hands properly, why assume they can use hand sanitiser perfectly?

Limiting other diseases is relevant as well though, as the goal is to not overload hospitals during a pandemic.

(+ just getting a cold is really annoying since I would need to quarantine more than I would with a cold before covid)

He's been a proponent of improved ventilation.

That's different from telling everyone to open their windows whenever possible. This is like cloth masking in that it's probably only going to help a little but it's easily at hand.

Healthcare, homes, schools, and workplaces should have been encouraged to improve ventilation at the very beginning of the pandemic, but tardy recognition of the airborne route by leading authorities in 2020 stalled any progress that could have been made at that stage.

I cannot relate with this judgment, regularly venting (about every 20 minutes, I believe) has been the standard in schools and day cares where I live for at least a year.

The plastic barriers that have become so common are an egregious example of this. They hurt air circulation and don't prevent transmission, but they're cheap and appear to do something. I've wondered why restaurants haven't started using some sort of fan attached to a high quality air filter, basically a cheap air purifier. And for more intensive usecases, why not have chambers that are sealed off and have a powered filter as the intake? I'm not the expert here so there's probably a good reason why, but it was a little weird seeing everybody focus on ventilators at the beginning of the pandemic instead of filtration.

Didn’t read the article? But in the US inside there aren’t plastic barriers. There will be no updating of hvac systems. I’m pro mask indoors, but favor places that are pro vaccine card. WA and OR were more appropriate to this than CA.

You will not, outside super heavy government subsidy, get better interior filtration in the US.

I say this as a business owner who could probably persuade the building owner to offset part of the charge, but the cost doesn’t make sense.

Also worth mentioning that this is historically not unprecedented.

During the Spanish Flu the agreed policy for the schools that remained open was to have outside classrooms for children, or in winter to keep the heating on but with all windows open.

Anyone heard about Corsi-Rosenthal boxes? https://cleanaircrew.org/box-fan-filters/. A box fan and 4 x 2 inch MERV 13 filters. Around $100, including the duct tape. This design is very effective, surpassing commercial air cleaners that are three times more expensive in independent tests. https://cleanaircrew.org/ufaq/does-the-corsi-rosenthal-box-w....

In Japan, ventilation has always been seen as one of the main ways to keep cases low. Restaurants and bars keep their doors and windows open, busses and trains have windows open, campaigns encourage everyone to open any windows in offices and homes for ten minutes every hour... even in winter.

Seems like the science supports thi snow but for many years foreigners in Japan have traditionally and famously complained about "how stupid it is to have the windows open in winter"... the table shave turned.

Tourists were laughing with people wearing masks in trains, buses and malls as well. Imagine the shock after March 2020.

Ventilation is energetically expensive, and can be even impossible to retrofit (windows that don't open, ...)

Purification however is energetically very cheap (just a fan blowing through a filter, maybe with a UV led, no temperature change). And has the bonus benefit of removing other dangerous particulate stuff from the air (dust, smoke, ...)

Heat exchangers can recover a large fraction of the energy lost through ventilation. Modern systems can even recover humidity from the air leaving the building.

Air purifiers are very loud and mostly effective at removing particulates. If you want to remove VOCs, formaldehyde and CO2 then ventilation is a lot more effective.

A well designed ventilation system can be completely inaudible.

> Air purifiers are very loud and mostly effective at removing particulates. If you want to remove VOCs, formaldehyde and CO2 then ventilation is a lot more effective.

Modern air purifiers are basically silent in normal operation, and there are models that remove VOCs and formaldehyde. CO2 is still best removed with ventilation.

> Modern air purifiers are basically silent in normal operation

Maybe on the lowest setting, but I doubt you'll actually have clean air on the lowest setting. Especially if you want to filter VOCs.

> Maybe on the lowest setting, but I doubt you'll actually have clean air on the lowest setting. Especially if you want to filter VOCs.

Have you actually used a decent air purifier or are you just guessing? There are plenty of models that do a good job filtering VOCs (as measured by a separate VOC sensor) and are almost silent in normal operation. A lot of the innovation in this space seems to be happening in Asian brands, I remember when I lived in London it was very hard to find good air purifiers.

I don't have an air purifier myself, but I've talked to people who own air purifiers and read lots of online reviews.

All I've heard is that on the lowest setting they are very silent, but on "auto" mode they start up regularly and are not silent at all, and if your room is anywhere close to the recommended size the lowest setting doesn't do much at all.

I was mostly researching about the Mi brand air purifiers, since they are readily available in Europe and a lot cheaper than European brands, but if you have suggestions for a brand that makes purifiers that are actually silent AND effective I'd be curious to hear about them.

The Mi 3H is a decent model (fairly significant improvement on the earlier models). I have one in my bedroom, and it really only cranks up the volume if I fry something in the kitchen and forget to run the extractor.

VOC levels (as measured by a separate sensor) were up around 400 μg/m^3 when we moved in — somewhat high, probably because the apartment was new — and after a week, during which the Mi 3H was on auto mode and always silent, I tested again and they were down around 120 μg/m^3. It also deals with moderate spikes in PM — like someone smoking on the balcony outside, or opening a dusty moving box in the room — without increasing the noise levels noticeably.

Automated ventilation saves energy. You don’t need to open windows anymore which leads to less heat or cold coming in. If your ventilation system has a heat exchanger it’s performing even better. It’s impossible to build highly efficient houses without automated ventilation.

Most office buildings also do not have windows that open at all.

These office buildings usually have automated ventilation which if specced properly can provide equivalent or more air exchanges per hour than open windows. As a bonus, automated ventilation can include a heat exchanger, while an open window can't.

Yeah, no.

Having literally every indoor space be freezing cold is not reasonable.

In the UK this happened earlier in the year (no-one cares any more) and generally everyone would huddle in the most sheltered part of a venue to make up for it.

And no, we're not installing magic new tech in every building.

Having literally every indoor space be freezing cold is not reasonable.

You are absolutely correct. I have heat and insulation to keep the cold out. And it works: It is currently -9C/16F and though I feel a small draft from the closed window, I'm also not wearing a coat indoors. I'd be huddling under a blanket otherwise.

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