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On whether changes in bedroom CO2 levels affect sleep quality (gwern.net)
576 points by pizza 3 months ago | hide | past | web | favorite | 306 comments

I was lucky to get my hands on 5 proper co2 sensors from university, while I was teaching and working. So plenty of test places.

What I found:

-Just a couple of hours in a office, without ventilation spikes the co2 enough to make everyone dizzy and tired by the end of the day. Keeping eye on the meter and ventilating properly, increased everyones productivity and people werent so tired by the end of the day.

- Classrooms, with 20-30 people are as bad. co2 rises really fast and makes people dizzy. Most often ventilation is too low, as a cost saving measure.

-Closing bedroom door, sleeping alone made bedroom as bad by the morning than classroom or office.

-Main culprit seems to be our perfection with insulating and making rooms airtight. I do live in a cold climate, so having open vents or windows is not common half the year. It seems it has not been such a big issue before plastic windows or in older houses. I think it is getting worse with every new building.

As someone who has built my fair share of houses and worked on many more over the last 25 years, I have to agree that our ability to seal air better than ever is causing problems, especially if you don't have forced air heating and cooling running all the time. People just completely ignore or haven't ever thought about room ventilation, positive or negative room pressures, and where and how to ventilate to the outside. In older houses there was always air leaks, small, but they let the house breath, especially if you had a central fireplace and your house was at negative pressure. I have seen many people purposefully over seal their house in ill conceived ways, to try and improve insulation, but end up causing ventilation problems with mold being especially common. Materials and vents that should let air pass through are commonly replaced with impermeable plastics and sealing tapes, many times in conjunction with a misunderstanding in expansion and contraction joints that have small gaps.

> As someone who has built my fair share of houses and worked on many more over the last 25 years, I have to agree that our ability to seal air better than ever is causing problems, especially if you don't have forced air heating and cooling running all the time. People just completely ignore or haven't ever thought about room ventilation, positive or negative room pressures, and where and how to ventilate to the outside. In older houses there was always air leaks, small, but they let the house breath, especially if you had a central fireplace and your house was at negative pressure. I have seen many people purposefully over seal their house in ill conceived ways, to try and improve insulation, but end up causing ventilation problems with mold being especially common. Materials and vents that should let air pass through are commonly replaced with impermeable plastics and sealing tapes, many times in conjunction with a misunderstanding in expansion and contraction joints that have small gaps.

Sorry, but this is just wrong and is the type of "accepted wisdom" that holds back construction, particularly here in the UK.

Repeat: ventilation and permeability are different things.

Yes, permeability can achieve some ventilation but it comes at the cost of:

1) Not being reliable; it is dependent on pressure deltas around the dwelling.

2) Being potentially deleterious to the fabric of the building where escaping warm air cools and water condenses on surfaces in the fabric.

3) Being wasteful of energy.

The solution is to separate the two:

1) Seal the fabric totally, bearing in mind vapour permeability. The seal should be on the warm side of the insulation.

2) Install a ventilation system which provides reliable fresh air and, ideally, exchanges the heat leaving the building with the fresh air coming in.

We can no longer rely on folksy wisdom. Let's engineer our houses.

You may be interested in the "perfect wall" concept by Joseph Lstiburek:

* https://buildingscience.com/documents/insights/bsi-001-the-p...

Also check out Matt Risinger. They both have various good content on building science.

Thanks for the reference. Trouble is there is no one "perfect" - depends on so many other constraints.

Apparently certain residential building codes have air-freshness provisions:

I recently added A/C cooling to a previously heat-only house, and I took the opportunity to ask the company to explain some quirks in the existing system, like how the ventilation fan in the laundry room is on the same breaker as the central heating, and had a hidden timer attached to it.

The house was built (early 1990s) with a particularly powerful vent fan in the laundry room which was on (regardless of the wall switch) a certain number of hours a day, and the forced-air system had an air intake outside the house which mixed with the return air before hitting the filter.

This was all sized such that all the air in the house would be replaced about once every 24 hours, according to WA state's VIAQ ("Ventilation and Indoor Air Quality") code.

That's all been superseded by the International Mechanical Code and International Residential Code.

See also ANSI/ASHRAE Standard 62.1-2016:

* https://www.ashrae.org/technical-resources/bookstore/standar...

I have a 100+yr old house, no vents. Old style radiator. Doors have large gaps underneath them, the holes on the floor that the radiator pipes travel through have gaps that you can feel the draft. It's annoying, but the house really does breath and is noticeable comfortable for me unlike houses with forced heat that are sealed well.

That draft you feel is money going out the (proverbial) window. It's better to stop the air going in/out through walls, doors, and windows, and bring it in in a controlled fashion:

* https://www.youtube.com/watch?v=CIcrXut_EFA

The problem is that many retrofits don't bring in outside air into the mix and just recirculate what's already in the house. This is not current best practice.

Any kind of air exchange will cause heat loss or gain, decreasing insulation. Does not matter if it's through wall or HVAC.

If there is no draft, it means there is no air circulation.

The only difference is if the draft goes through HVAC vents or through unsealed doors and windows, or through walls.

If your local heaters are effective and seal controllable, there should be really no difference in many municipal settings as the heating is waste heat from electricity generation anyway. (Those cooling towers "greens" love to hate.)

Certain baseline air flow is strictly required and it is quite a lot, especially in small volumes.

Now, if you have to burn something to heat, then by all means do install a heatpipe recovery system.

You're not wrong, but one can mitigate energy loss with an HRV (or ERV) and get fresh air in a controlled manner:

* https://en.wikipedia.org/wiki/Heat_recovery_ventilation

With the added bonus that the air can be filtered as well, instead of coming in as-in through leakage.

And I recently remember hearing forced air is bad for air quality inside! Did I hear wrong or is there something more to the story like “forced air brings in outside air, so if your outside air is bad you’ll have trouble”?

Most residential forced-air systems don't bring in air from outside (intentionally at least). They recirculate the air in the building through the heating/cooling unit (typically a combination updraft furnace with AC evaporator sitting on top).

Modern systems (since late 80s, maybe?) have return air ducts so that you get even heating even if interior doors (e.g. bedroom doors) are closed, but older systems may only have one return vent per floor or even just a single one in the house, and depend on gaps under doors and such for return air circulation.

Bigger commercial forced-air systems have had exterior air intakes and heat exchanger systems for a while, but are pretty new for residential (I've never seen one in the wild myself).

Heat recovery ventilators [1] are reasonably common in Canada. Most (all?) EnergyStar homes [2] have one, and they includes most if not all the houses I've looked at (or friends have bought) in the past decade or so.

I lived in a house built around 1985 that had one, which was R-2000 [3], so they're at least that old.

[1] https://en.m.wikipedia.org/wiki/Heat_recovery_ventilation

[2] https://www.nrcan.gc.ca/energy/efficiency/housing/new-homes/...

[3] https://www.nrcan.gc.ca/energy/efficiency/homes/20575

Oops, I meant houses that were built in the last ~decade are mostly EnergyStar.

You can add filters on the blower to clean up the air. Especially important in cities.

Also important in the middle of nowhere when the clean, forest air turns to smoke each August.

This is a bit of a side quest comment.

South Africans are (at least historically) quite different in this respect. Everyone is cold in the winter due to complete disregard for insulation (at least, when compared to Europe). People also don't get layering. The comments about construction do hold mostly. In the warmer areas of the country usually you are cold in the winters for only a couple hours per day.

When we go overseas we tend to open all the windows. Maybe this is because we are not used to long winters.

My grandparents were experts at opening select windows in their houses to create drafts in the pre-aircon age.

There is a meme: "If a guy invites you to a braai at his home at 3am, it really is a braai."

A house should not breathe. A catchy mantra I've run across is "seal tight, ventilate right":

* https://www.youtube.com/watch?v=CIcrXut_EFA

Mold is not a ventilation problem, but rather a moisture control problem. Keep the humidity down (especially with whole house dehumidifiers), and eliminate condensation points (by eliminating thermal bridging), and it goes away.

While the above video, which is from the really good channel by Matt Risinger, is a good introduction, I recommend you also check out the building science stuff put out by Joseph Lstiburek for a more science-y explanation:

* https://en.wikipedia.org/wiki/Joseph_Lstiburek

On the "perfect wall":

* https://buildingscience.com/documents/insights/bsi-001-the-p...

Presentation on control layer (especially starting around 15m):

* https://www.youtube.com/watch?v=rkfAcWpOYAA

Good webinar:

* https://www.youtube.com/watch?v=sBcNFeiWjrg

> Mold is not a ventilation problem, but rather a moisture control problem. Keep the humidity down (especially with whole house dehumidifiers), and eliminate condensation points (by eliminating thermal bridging), and it goes away.

This sounds like one of those kinds of answers that only works with spherical cows in a vacuum.

If my shower were completely open and in the middle of the living room, perhaps. Alas, it's in a small private room that usually has the door closed while in use, and now we've circled back around to ventilation...

Yup, ventilate right:

* https://www.youtube.com/watch?v=Ulaz3aUSZlQ

* https://www.youtube.com/watch?v=-3CRGhu8C5I

There are houses that are almost hermetically sealed, and do not have issues because they control temperature and humidity properly:

* https://en.wikipedia.org/wiki/Passive_house#Airtightness

> A house should not breathe Well - first you have to define what "breathing" is, because I've talked to tradesmen who thought it meant allowing air in and out...

Closer to the correct definition shared amongst building scientists is to allow the passage of water vapour. Many engineers would disagree with the approach of having non-breathable walls. If you're renovating old properties you are putting a LOT of faith in your VCL if you go this route.

I like the concept of breathability personally, allied with high air tightness. But you have to use the right materials and, crucially, install it right.

Yes, moisture transport is a lot higher with air leakage:

* https://www.ecohome.net/guides/2316/the-difference-between-a...

However, if you're doing an air barrier, you can often get a moisture barrier "for free" nowadays. Since a lot of housing uses OSB/plywood, if you go with something like Huber's Zip System--which has a coating on it--you can save a lot on labour by only doing one pass around the house. Though you do have to seal the seems as well.

Otherwise something like the popular Tyvek will get the job generally done, but there are peal-and-sticks as well that tend to be tighter (and vent as well, like Delta Vent).

If one is okay with the cost, there's also the idea of simply closed cell foaming the entire house. :)

What's the solution?

My house is absolutely frigid during the winter, and I got quote for resealing it. He told me that afterwards I am either going to have to leave my windows open (no thanks!) or live with mold.

I've heard that you can install vents, but can't find useful info. My grandparents had a chute vent, and it somehow became a breeding ground for flies and all sorts of ichies. Not sure why.

And short vents sound to me like an always open wondow, which just brings in the cold.

I want the insulation, the circulation, the breathability and the warmth. Is there any way to have it all?

Heat recovery ventilation can bring in fresh air with about half the heat loss, but it needs regular maintenance.

You can also look at whole house dehumidifiers to take the water out of the air to help reduce the mold problem.

Yes. Matt Risinger has a really good channel on building science, and this video is a pretty good intro on air tight houses and ventilation:

* https://www.youtube.com/watch?v=CIcrXut_EFA

Go through the archives as well. Lot's of good stuff.

He's based in Austin, TX, so needs to worry about heat and humidity being kept out, but the principles also apply for colder climate where the cold needs to stay on the outside.

Another good person is Lstiburek, and his concept of the "perfect wall":

* https://buildingscience.com/documents/insights/bsi-001-the-p...

My friend studied Interior Architectural Design, one of his professors there started one lecture a year by getting the CO2 sensors, placing them around the lecture hall, showing the readings at the start of the lecture, closing the doors and then after the hour long lecture showing the readings.

During the lecture he mentioned the figures for CO2 concentration that led to symptoms, e.g. dizziness, sleepiness etc.

The reading at the end of the lecture showed that it was over the recommended limit, and well beyond the threshold that causes people to get sleepy and lose concentration. (I believe it was less than 400ppm at the start and thousands ppm afterwards?)

A simple demonstration using an older building crammed full of students in a closed space, but it was apparently quite impactful in showing the students how there are a lot of features of interior design architecture that aren't really addressed and are only coming to the fore recently.

This now makes me wonder if there is another dimension to the “people who get in early or stay late are more productive than those who work traditional hours.”

I’ve attributed this to “fewer people, fewer distractions.” However, with a CO2 component... hmm.

Well, there is another project idea. Arduino with a CO2 sensor and plotting a running total. Or not displaying and instead have a “I feel productive” dial that would allow for correlation to the recorded data.

>there are a lot of features of interior design architecture that aren't really addressed

Nearly every standard rectangular building should be in actuality built with the energy efficient building design in mind, but we don't... out of simple mental oversight and in the increased cost in construction.


Literally, we could save 20% to 30% in energy costs with every building with possibly only 10% to 15% increase in cost of construction, but we simply don't because we have no congregate valuation of resource consumption, only individual guilt.

Maybe this is why I would feel sleepy during lectures. I always thought it was because I was mismanaging my sleep or the teacher was boring (it was probably a combination of the three).

This might also be the reason individual and small-group learning is more effective - there's less CO2.

Wouldn't that be a wacky turn of events, for all those studies showing that smaller class sizes produced better outcomes, to end up being mostly attributed to lower co2 levels in smaller groups.

This might be a really stupid question but, wouldn't you _want_ sleepiness when you, I don't know, try to sleep?

I think the answer to your question is, yes, however you want to be sleepy due to a need for sleep rather than impaired function.

CO2 is damaging to your body, I am not an expert in these matters however I know that much.

Becoming tired due to CO2 is in effect a minor form of gassing yourself, and during sleep high CO2 is bad for you and I would assume does not give you high quality sleep - same as alcohol makes can make you drowsy while also interrupting your sleep.

"Natural" sleepiness has none of these downsides.

Do you have some followup sources for these fairly strong claims?


Most of the claims are trivially verified true with a proper understanding of hypoxia and the effects on the brain.

Of course you want to be sleepy, but you don't want that sleepiness to be due to hypoxia because hypoxia is known to damage the brain.

Hypoxia is about oxygen levels, not CO2 levels. Those are definitely related, but not at all the same.

The link you gave makes me think I actually have to dig through quite a few studies to find something supporting what you said (it's not on the first page, for anyone wondering), which is why I asked for direct sources.

> to find something supporting what you said read the username, I am not OP, and did not make the claim.

A simple search of "hypoxia from excess CO2" brought up https://en.wikipedia.org/wiki/Hypercapnia, which also support the claims.

Please, for the love of god, learn to google properly: http://www.catb.org/esr/faqs/smart-questions.html

Followup rhetorical question: Do you like waking up sleepy and dizzy?

But not in the morning.

> I believe it was less than 400ppm at the start

Then this must have been before 2016. Atmospheric CO2 concentration has always been higher than 400 ppm since that year.

+1 here. I worked at an IoT startup with a lot of gas sensors. When we tested the CO2 sensor, we immediately noticed a correlation between early-afternoon sleepiness and high CO2 levels. Opening the door to the outside world lowered levels and within 5 minutes we felt more awake. It changed how I work: I still like to be warm and cozy, but now I'll bundle up and endure changing the air rather than seal every door and window as I used to.

I feel like most of these experiments don't control for air temperature. I feel like cold air has a much more rejuvenating effect than just lowering CO2 levels. Not that they don't matter, but it's not like you'll instantly feel better.

Why won't you "instantly" feel better? Instant meaning a few breaths of outside air, anyway, likely well within the claimed 5 minutes.

This is wildly conjectural, but assuming the "CO2 is causing widespread cognitive problems" hypothesis is true, I wonder if there are whole colleges whose student bodies are getting slightly worse grades because of this. There are a couple of small colleges in my area that are regionally famous for their stuffy buildings.

I wonder similar about office buildings or apartments which are next to large car-parks, does that measurably affect air quality inside?

If most of the cars in the car park are turned off, it might not be any worse than a building next to a busy highway where cars are actively spewing CO2.

The worst would be a small leak of CO (not CO2) , even in very small quantities, daily miligrams of CO coming from a leaky(small leak) Gas burning heating system. This will most probably get students scores down, among other extremmely bad health effects.

Bigger CO leaks are extremely dangerous, many people lost their lives because of heating systems.

If you can, change to Oil Flow system with burner outside the house and far and aislated from humans. Or, if you can, electrical system. CO from gas is Really Very dangerous.

(using the word "very" is against Mark Twain's advice[1], and using the word "really" is against my own advice, but there are exceptions, here above was one)


“Substitute "damn" every time you're inclined to write "very" ; your editor will delete it and the writing will be just as it should be.”

                  Mark Twain
2- "delete all instances of "really" in you text, and your writing will be better"

ImmerseintheImmensity, Also unknown as InfimousInfinity, Also unknown as ParadoxParalax

Curious if you have a link to what sensors you had? Think this is cool and i've been on/off looking for co2/o2 sensors greater than recreational precision

Can’t speak for OP but I’ve been using the IQAir Air Visual Pro and can support everything they’ve said. I try to keep CO2 around 400-500 in my office and home but it spikes surprisingly fast with even one person breathing in a medium sized room.

It can integrate with HomeBridge and has a good API and unlike a lot of IOT stuff it’s well supported and stable.

do you know how accurate it is?

It seems pretty accurate. The South Coast Air Quality Management District tested a bunch of consumer devices against a $30,000 professional device. I was deciding between the IQAir and Laser Egg 2+, which both did well according to their tests http://www.aqmd.gov/aq-spec/evaluations/field. I got the Laser Egg 2+ the other day. It's really enlightening to see how it spikes when we cook dinner or lunch on the gas stove.

Does the Laser Egg 2+ monitor CO2? Looking at the kaiterra product page [1] I don't see it

[1] https://kaiterra.com/compare-page/

Pretty accurate, there was an air quality report which compared about 3-4 samples of them with commercial air monitors - the lab found them adequate with some but not massive sample variance. They were the best of the consumer models tested.

Can’t seem to find the report but to be honest I stumbled on it while searching for PDFs on the subject a year or two back. (I own no stock nor have any affiliation with IQAir - just a satisfied customer - high price not withstanding).

They were too expencive to buy recreationally, at least for me. Evikon, small company that does science instruments. Sorry, cant find the model anymore, I think it was discontinued.

I do belive now though that even having recreational level sensor will give you at least understanding overall co2 levels and this something we should look into more.

I founs a paper using the same sensors that measured co2 in schools. In all cases, at certain times the measurement was higher than norm. occassionally over 2000. I can now understand much better kids getting sleepy and unable to concentrate in classroom.

Paper sadly in Estonian only: https://www.google.com/url?sa=t&source=web&rct=j&url=http://...

For a couple hundred bucks you can get a highly accurate CO2 sensor that reads out via a USB-serial connection: https://www.co2meter.com/products/k-30-co2-sensor-module

Try MH-Z14 or Z19.

Are atmospheric CO2 levels rising to an extent that currently projected levels would have a noticeable effect in the same way?

We're on track to reach 1000ppm by the end of the century, if levels continue to rise at their present (accelerating) rate. This is about the threshold where cognitive effects become reliably detectable. However, such levels also bring climate change on such an apocalyptic scale (4.5+ degree temperature rise) that industrial activity could well wind down as society collapses.

This is absolutely not true.

The predicted number is much closer to around 650 ppm, and that's assuming no change.

In reality, things like solar technology have massively gone down in price over the last couple decades, and are only continuing to reduce in price.

We will likely see 2-3 degrees of warming, but no credible scientist is making the predictions that you seem to be making.

I suppose the question is, predicted by whom? And no change in what?

If there is no change in CO2 emission, then yes we might restrict the total damage to 650 ppm. But "no change in CO2 emission" doesn't mean "business as usual", it means a moratorium on all kinds of expanding industrial activity.

Not only are CO2 levels increasing, but CO2 emission rates are increasing. Hell, the first derivative of CO2 emission rate was also increasing until the past couple of years, a minor but happy development that could easily snap back. "Business as usual" means an exponential curve.

Solar powered industry is still a far-off pipe dream. Even if it only takes 30 years to replace all energy sources with sustainable alternative, in 30 years huge damage will have been done. We cannot afford to just shrug and say the problem will just solve itself.


> I suppose the question is, predicted by whom?

As predicted by the scientific consensus and the intergovernmental panel on climate change.

Disagreeing with them on this is no different than being a climate change denier, TBH.

The right thing to do is listen to the opinions of the experts, and this is what the experts believe and is the scientific consensus.

> The predicted number is much closer to around 650 ppm, and that's assuming no change.

Though solar and other non-carbon energy sources are coming down in price, world energy needs are outpacing them. Out CO2 emissions are increasing, not decreasing. I doubt that we'll see 1000 ppm by the turn of the century, but if the "no change" projection is 650 ppm then by simple matter of inference, due to increasing CO2 output, we should be higher than that.

What I am saying is, that we will get to the point where it literally doesn't matter if world energy demand is increasing or not.

Why? Because if solar power and others, continue to go down in price, as they are doing now, then solar ect will be cheaper than coal.

From a purely economic stand point, countries will eventually just stop burning coal, because the alternatives are just flat out cheaper, even when you ignore the costs of global warming.

That point in time, when alternatives are just straight up cheaper than coal, isn't too far away.

From a certain level of abstraction, if countries always did the economically rational thing, we wouldn't be in this mess at all. Building out solar capacity requires planning and foresightedness and political will. Hell, America could transition entirely to solar power for a fraction of the price of the Iraq war - in that sense, sustainable power is already cheaper than carbon-based, once you factor in the externalities of middle-eastern instability. If you factor in all the externalities - pollution, environmental destruction etc - then sustainable has been "cheaper" for a very long time.

The trouble is that countries are not purely rational, and do not factor in all externalities.

Or maybe Solar will never be the environmental fix-everything that people hype it as - https://www.youtube.com/watch?v=ciStnd9Y2ak


Why was it so important to you to say something so perversely selfish that you felt compelled to make a throwaway account to do so?

That's an attitude that we can all apsire to.

Probably still going to be your family's problem..

Not with that attitude :)

Indoor air co2 only lowers due to outdoor filtration. So, higher outdoor co2 will make us reach higher indoor levels faster. A change of outdoor air to 500 from 400 ppm, for example, means there's 16% less difference with indoor air at 1000 ppm.

All/most modern houses (10-15 years old) have central ventilation systems here. This allows for great insulation while also having great ventilation. The central system sucks out warm air from bathroom/kitchen and uses it to warm up incoming air from the outside.

What level was it at when you started noticing those effects? And how did you measure productivity?

I have a sensor and try to keep readings low. My girlfriend isn't quite convinced though, especially in winter....

Around over 2000 I think. Less than 1000 would be ideal, I think outside is around 400.

Yeah it never gets above 1300 at our place with windows closed. With a window open a crack it stays at 700-1000.

Outside is 400 globally but often 450 or more in cities. At least on my meter.

My previous employer had excellent air quality and I often stated this to others as one of the things I liked about working there. A lot of people look at you kind of funny if you say that but it really was remarkable, and I really felt a difference when working in that building compared to when I went to school and a lot of other places where you stay inside for a prolonged time. I felt much less tired there than most other places!

It seems it has not been such a big issue before plastic windows or in older houses. I think it is getting worse with every new building.

That's because the focus on energy efficiency means installing HVAC that recirculates and setting the recirculation ratio to as high as they can get away with. Before that, buildings were taking in 100% outside air to heat/cool, which was extremely inefficient but also gave no chance for CO2 to build up.

> buildings were taking in 100% outside air to heat/cool

This hasn't been true since fireplaces stopped being used for heating. Even very basic furnaces, such as the coal-fired one my grandparents had in the 1940s, recirculated the air inside the house. (It was an unforced / gravity "octopus furnace", fired with soft coal, with the house temperature controlled via a damper on the chimney.) But it took its combustion air from inside, and was vented via a chimney to the outside, so the house was constantly at a very small negative pressure, and combined with the natural draftiness of prewar construction there was naturally some fresh air intake. But certainly not 100%!

I think it's the newer high-efficiency furnaces where you start to have very high recirculation ratios and consequent CO2 issues. Because they pull combustion air from outside, there's no incidental exhausting of interior air to outside (which would tend to pull in outside air through gaps in the building envelope). Great for efficiency, though.

Can you suggest a commercial CO2 sensor that you think is accurate enough? Most of the ones available on Amazon.com seem to be quite amateurish.

Vaisala makes good probes, acceptable for use in life science applications. They are expensive and you need an rs485 adapter for the ones I used. The serial protocol is nice and simple though.

Air tight buildings need a heat recovery ventilator.

Any ventilator. Heat recovery is optional - it is really hard to recover heat from lukewarm air without actually recirculating most of it.

The pressure drop requires more electricity due to more power in the pumps, making it a relatively bad trade - only heatpipe systems are worth anything.

Wow. Didn't realize how important it was to aerate. I seldom open the windows at my place.

I also remember often getting really dizzy working in my previous office, and I couldn't understand why, maybe you're on to something.

Now I'm wondering how all of that has affected my health along the years

The recommendation here in Denmark is to air out for ~10 minutes, 3 times a day, ideally with all doors and windows open, making sure to get good airflow between rooms.

I think very few people actually air out that much, but I've found that it's very helpful for my sleep quality to air out just before I go to bed. Airing out in the morning also helps eliminate moisture from showering, as my bathroom doesn't have a window, nor any forced ventilation.

I've certainly worked in poorly ventilated offices, and my bedroom is even worse. But I don't think I've ever gotten dizzy in an office. Is this something that affect different people at different rates?

This is one of my regular arguments in the office, I open a window, someone says "aren't you cold??" and I say "I don't want it colder, I want it fresher, less stuffy".

Your anecdata has cemented it as fact(tm).

> I think it is getting worse with every new building.

Only if you skimp on HRV system (which are cheap and works like magic).

It's lame to say it's getting worse, when it's actually getting better.

What i found is that i can open a window to bring fresh air in but togather with it magnitude of pollution that causes cancer and asthma...

Not a great choice if you ask me.

Move out of Beijing right now. Or out of Hebei province, or faraway from North Henan Province. Just move as sson as possible to a place with good air.

It does't not worth the money to live in Beijing, no matter how rich you can get there, and you can get rich there, but it simply does not worth.

Your life is more important, specially if you have kids.

I live in Poland and we are the lungs of Europe, still air is polluted as hell.. i dont wanna think how bad it is in other countries. And its not so easy to move out if you dont have enough of money.

Yes, you are right. Not easy.

But I am happy to know that Poland's air still can breath, at least, compared to India or China.

I have been in Szczecin‎ city once, and I love Poland, and I specially love the Polish people.

Wish all good for you guys over there, and that the air gets better in the future, we need to hope.

Check out ERVs, energy recovery ventilators.

How are these different from HRV - Heat recovery ventilation?

HRV's exchange only heat. ERV's (where E stands for energy or enthalpy) also exchange moisture. One is not strictly bette than the other, it depends on your house and your climate: https://www.greenbuildingadvisor.com/article/hrv-or-erv

These require a ducting system, correct?

Not necessarily. There're units that are installed in, basically, hole in the wall.

This makes them very attractive for older renovated building, which used to rely on drafts for air circulation.

There was a link in the comments on this site awhile back from a company that made on similar to an AC window unit, and it had an optional active HEPA filter add-on, whick looked similair to a portable ducted AC.

Also, Panasonic makes a bathroom fan ERV for about $400, which you can find on Amazon, with two ducts, one for fresh air intake, and the other to vent the stale air, and you need to have the intake and exhaust ideally on opposite sides of the structure.

Some people use it for their basement humidity levels. It is much less expensive to run than a dehumidifier.

do you have recommendations for CO2 sensors?

There was an NBA coach who use to obligate his players to sleep with at list some inches/centimeters of air access in their windows hotel rooms the night before playing an important game/match. Don't remember what Team.

Surely he'd have to tuck them in at night to verify that...

Could see the windows from outside the building, probably, without needing to wake the players up, if that was his wish at a certain point of the night.

Colder temperatures also generally help people sleep.

I'm pretty sure I read 68F is the ideal sleeping temp

That depends if are an an Ianomami[1] born in Brazil or an Inuit[2] born in Denmark.

1- https://en.wikipedia.org/wiki/Yanomami

2- https://en.wikipedia.org/wiki/Inuit

: There is a risk, not for the Ianomami that are somewhat numerous, but that some other in Brazil are going to Extinction soon, after the last elections in that country. Only if they could move to Denmark...Or Northern Canada, where there are Inuits too. But North Canada recently is so full of political "moon landing" deniers that they probably would not be very welcome there. But Greenland is far enough from "civilezed" people. But they will have to learn how to hunt monkeys and collect mango fruits in the north-pole.

Don't know if above is getting downvoted by the the rightists or by the leftists here, what is fun. But probably getting d.v. because of being too caustic, too snarky and too ironic, what is not fun and I confess I deserve.

And, most important off all, I am getting downvoted for being Not polite to xeromal, and I apologise to xeromal for this. My comment sounded like he was being discriminative or something like that, what is not true, and off course I should have found a decent way of pointing that the ideal temperature to sleep varies from person to person. And off course, I should have avoided going astromically off-topic. But will not delete the comment, to let the lesson there for myself.

Irony is really not welcome, I have to make an effort to understand that and abide by rules and follow the recommendations.

But giving or asking explanations for up or down votes is equally Not recommended and not welcome, sure.

Better to abide. Otherwise just do[1] like Bender Bending Rodriguez of Futurama.

The original quote from Bender is: "I will make my own Lunar(really on the moon) Amusement Park, whith Blackjack,... and Hookers!!!. ...Well...forget about the Blackjack...You know what?...forget about the Park too."

1- https://i.kym-cdn.com/photos/images/original/000/348/790/b3f...

Hi, I didn't downvote you, but hopefully I can shed some light on why other's did.

This is a conversation about the levels of CO2 and how it effects a person, especially their sleep. In this part of the conversation people have started to talk about how the temperature also effects your sleep. This was a natural progression, as less CO2 needs more ventilation, and brings with it colder temperatures.

You then started talking about two groups of indigenous people in different climates. Brilliant, I'm interested in how these two groups of people sleep! You however did not talk about these people's sleeping habits (as would have been another natural progression for the conversation) but instead go completely off the topic of conversation and talk about a bunch of unrelated topics, with very tenuous links between them.

Your comment did not add to the conversation, at all. Neither has mine of course, but I hope it goes some way to explaining the unpopularity what you said.

Thank you Balero, I hear your words.

Only see this your comment now, long time after.

But Thank You for taking your time to help me seeing those things, really.

Cheers and wish you all the good in the universe!

Thank you!

I've worked on environmental sensing iot projects and have seen the cost of co2 sensors. Almost all the cheap ones are VOC sensors which infer a co2 level by assuming the VOC output is from humans (rather than paint for example).

Given the cost of the device I would be amazed if it wasn't a VOC based sensor. The cheapest CO2 sensors I've seen are well over $250, even in bulk. CO2 is quite innert, so it requires very precise and accurate components

Looking at their materials[1], it's IR based and needs calibration. I'm sure it's output is interesting, but likely not super accurate given their started assumptions for the calibration process. Better sensors may be required before drawing any conclusions!

[1]: https://www.netatmo.com/en-gb/helpcenter/air-care/4/installa...

i’ve noticed this casually as well. i bought an airthings wave plus [0] a few months ago and the co2 and total voc readings seem pretty (but not perfectly) correlated.

i live in a drafty pre-war building and my co2 peaks at around 1500-1600 ppm at night with doors and windows closed. it troughs at around 500 during the day when i have the doors and windows open (~400 is ambient from what i understand). tvocs typically peak around 600 ppb and trough at around 20 (under 100 is considered safe iirc), with the same cycle as co2.

[0] https://airthings.com/us/wave-plus/

413ppm is now ambient. Goes up higher every year (with a small amount of seasonal variation).

By 2100, we may be at 800ppm if we continue and/or accelerate fossil burning (4 degrees C trajectory). https://www.co2.earth/2100-projections

Already a middling stuffy room, and would increase indoor levels 400ppm over today.

I wonder at what point will people have active systems to lower their CO2 below ambient in their homes.

You mean plants?

You need an enormous, full sun greenhouse just for one person’s CO2:

“An active person exhales about 1 kg of CO2 per day. So, you would need 1000 square meters of grass to absorb one person's CO2. That's a square about 32 meters on a side, or in archaic units, a quarter acre. A one-square-kilometer park could support 1000 people, just with the grass.“

(Or: Need about 16 trees per person.)


ha, i actually bought a bunch of plants from the nasa list a year-ish ago to help reduce co2 & voc levels: https://www.healthyandnaturalworld.com/best-air-filtering-ho...

Did you notice a difference? We have a small office with two people, multiple PCs, printer, etc. It gets warm and stuffy regardless of the season and climate control, and I have trouble focusing especially in the afternoon.

I'm thinking of picking up a plant or two and pointing a fan at the door to send out some of the stale air.

To get a better filtration effect you need to force air into the root zone through an active carbon layer in the soil media. That is the method used in the original nasa paper and subsequent public labs designs when trying to remove VOC's such as those emitted by printers. Active carbon adsorbs the VOC's so that the root microbes can metabolize it. Since it is a microbial filter, it becomes more effective at filtering the contaminants that it's most exposed to. Active carbon can also remove CO2, but must be recharged with lower CO2 air periodically.

The public labs design uses a aquarium bubbler to push the air, but the flows are pretty low - with retention time in my 10x12 office at 1 month. Since the VOC's are usually heavier than air, if you place the pump inlet on the floor it performs better though.

i felt a little better but honestly i think it was more placebo than anything. i didn’t have the IAQ monitor before getting the plants so i can’t know for sure what the air quality effects were.

i got 6 plants (but 1 died) and they make my living space feel more lush and comfortable, which i count as a win.

i did also eventually get a air purifier (blueair 211+) and that’s probably the main workhorse at night with the doors and windows closed (which is when i need it the most). i noticed a clear drop in allergy/asthma symptoms (sneezing, coughing, headaches sometimes) after getting the air purifier.

so a fan at the door will probably have the best bang for the buck for you, but plants are nice too. =)

Can you recommend the lowest cost CO2 sensor that one can buy that would give reliable readings?

The "TFA Dostmann AirCO2ntrol" devices are popular in Germany. Searching for "co2 meter" on Amazon.com one of the top results is an identical looking device.

It measures with an infrared spectroscopy-based sensor, which should be quite accurate. There are a few good software packages for recording data, e.g. https://github.com/vfilimonov/co2meter.

Repost from my comment above, but for a couple hundred bucks you can get an accurate CO2 sensor that reads out via USB-serial to a computer. I use them at work and we've shown they are quite good over the long term. Plus to recalibrate, you can just take them outside. https://www.co2meter.com/products/k-30-co2-sensor-module


I have developed custom Ethylene sensors in the past for customers, and Dynament (UK) is a manufacturer that I can definitely recommend if anyone wants to do this and go down the DIY electronics route without having to dig through a bunch of Chinese products to find the "right one". https://www.dynament.com/products/gas-sensors/standard-non-e...

Cool! I worked at an ethylene-sensing IoT startup (fruit ripeness natch). What was the core sensor you used? (We were using off-the-shelf, but somewhat pricey, electrochemical sensors)

"MSH-P/HC/NC/5/V/P/0 - 3% Volume Ethylene = 0.4V - 2.4V"

We built that into a custom SS body with a Delrin mounting insert, and ran the serial connections to a custom board that interfaced with up to 8x sensor locations (in conjunction with some other sensor elements). The elements were ~US$200/ea ~4.5 years ago.

These are fancy interpolated IR absorption sensors internally, so any gases of similar concentrations could throw off the readings; depends on the environment. Would be BEST to calibrate to local atmosphere conditions of the installation, but that's not really something you can sell. :P

I remember looking into this years ago, and the prices were in the $100-$200 range for low volumes. Was this your experience?


I got an NDIR CO2 sensor on AliExpress for $20. Do you think one of those would just have low accuracy or be uncalibrated?

I suspect both! I should compare a $250 one with the $20 one

That would be a worthy HN post.

Is that something HN is interested in? I do work and research with remote environmental monitoring stations and am always comparing sensors. Currently doing a precipitation gauge intercomparison study.

I can only speak for myself and what I've seen discussed here over the years -- yes, it would be interesting. Why is better stuff is more expensive, how to make the cheap stuff work closer to the better stuff, and interesting findings from actually using them. Lessons learned are always interesting...

Please do! I just bought a couple of cheap co2 sensors on Amazon (2k positive reviews) only to find out that they may not be accurate.

It would be amazing if you or anyone really could make a comparison between different models - and show whether the cheap ones on amazon and the likes are worth it.

Very interesting.

Would be interested to find out because if its just uncalibrated plotting out the relative differences it still would be useful (e.g. seeing a X% increase on whatever scale the sensor using at night versus day could provide enough of an indicator that something is going on and more investigations are warranted.)

Just test/calibrate them outside (400-ish ppm). Even if absolute measurements are bogus, they should do just fine to figure out whether it’s time to open the window..

Also if someone is searching for PM2.5 particle monitoring:


Thanks. I was about to get a cheap one on Amazon :D

Sort of related, I'm living in a newly constructed house and I'm interested to know the indoor air quality. Any recommendation for a comprehensive in door air quality test solution (either device(s) or hire someone maybe)?

MH-Z14 or Z19 are cheaper, around 25€. With optical measurement. I have a few of them, they seem accurate enough. I calibrate them every 6 months by placing them outdoors.

Are there any brands or products you would reccomend for measuring CO2 in my house? Ideally with some way to hook it up to my computer.

It looks like things have moved on quickly since the other year when I was more involved in this! This company does some good products, some of which are fairly easy to interface: https://www.gassensing.co.uk/products/

This is especially pronounced at high altitude, and when running a furnace in the winter. I keep large black tents (4x4 ft or 2x4) in every bedroom in the house, and grow kale, spinach, chard, peas, tomatoes, etc inside (with handmade COB LED lights).

I don't have any sensors to get a real idea of the difference in CO2 it makes, but it allows us to run the furnace less at night (heat from the lights), and makes a noticeable difference in humidity ( very dry air here ).

Also, we get about 1-2 family meals / week of food at full capacity ( total 4x8 grow space and 800 watts of light running only at night ).

Not economical and takes a lot of maintenance, but it's a fun hobby from which we all feel the benefits.

Have the police visited? Sounds like the sort of thing they'd think would be a grow house. (....a marijuana grow house, I mean, not one for eggplants and radishes)

800 Watts for 12 hours a day is about a hot tub worth of draw.

I reckon it would be tough growing eggplants indoors with LED light.

Fruiting plants are a pain because you have to shake them to pollinate. We mostly stick to leafy stuff. The lights are incredibly bright, top of the line horticultural COBs. They are not the pain point.

It's unlikely you'll have a noticeable difference in co2 levels with indoor plants, even considering your unusual setup.

I think it’s as simple as biomass produced vs biomass consumed, and I agree a 4x4 garden is not going to fully replace O2 for two sleeping adults. I’ve experimented with building tower setups which would allow 3-5 times the biomass growth in the same space, but it’s a real pain tending to a garden at eye level, and introduces all kinds of new catastrophic failure possibilities when you have water above high power lights.

Nurses used to take plants out of hospital wards overnight because photosynthesis (input CO2 output oxygen) only happens in the daytime, leaving just respiration (input oxygen and output CO2) at night.

> but it allows us to run the furnace less at night (heat from the lights)

Dear God, what's your power bill? There's no way a LED lights heat is as efficient as just using the furnace.

edit: I meant cheap, not efficient.

Theres no difference in heating efficiency for any source. Heat is heat and it doesn't really matter if it's generated from a heating element in a furnace or an LED light. And with the light you're at least getting dual use out of it.

If they have a gas furnace it might be different but that would also depend on how their electricity is generated.

Your statement is true if the electricity is generated locally, otherwise there's a difference in energy losses depending on the carrier.

According to http://web.archive.org/web/20180822025250/https://portfoliom... heating with grid electricity would require 2-3 times as much primary energy as heating with water/oil/gas.

Especially if you have central heating.

except a heat pump which is far more efficient

Until you get to below zero.

I don't think that's quite true. The efficiency merely falls to 100%. (The laws of thermodynamics demand it.)

Now, converting electricity to heat may not be as cheap as converting, say, natural gas to heat (thus making the heat pump un-economical when not pumping any heat)... but you do get heat out of it.

That's true. But heat pumps don't have the gross energy capability as a gas heater. To get the equivalent of an 85,000 BTU gas furnace you'd need to be pumping 25 kW through your heat pump at that point.

I think one reason heat pumps have become more practical is that homes are now better insulated, making 85kBTUs of heating capacity excessive for all but the largest houses.

We've got an old, poorly insulated home which is why our requirement is so high.

The average is 30 BTU / 1000 sq feet. That's 10 kW / 1,000.

They now (as of 2018 I think) make Extra Low Temp heat pumps, which can work down to -15F. I think that makes heat pumps practical for a very wide variety of temperate climates.

I see they do, but their BTU's are very low - I see the Fujitsu RLS3H, which goes down to -26C only outputs 12,000 BTU at that temperature. To heat a house at that temperature you'd need 5-10 (if not more) of those.

Only if you insist on the same duty cycle. Furnace might only run 4h/day, while heat pump could run all day (6* reduction)

Yeah, I was thinking gas furnace. Also the heat would be localized to a couple of areas and not the whole house heat that a furnace would probably provide.

Extra $38/m, and because the heat is targeted we can leave the unoccupied areas colder.

Certainly not an efficient way to heat the house, but the main concern is oxygen and not generating co2 with the furnace, then air filtration (SLC nasty air), then humidity, then food, THEN heating.

edit: we vent the tents directly at our beds

Assuming the furnace is electric too, they should both be the same efficiency, since 100% of the power is being eventually turned into heat, unless the light from the LEDs are going outside.

So, assuming you have an electric furnace, it basically costs nothing to run all the electronics in your house? (Also assuming it's cold enough outside that you never want to cool the house.)

I guess the water heater might cost some money, since it produces heat, but a lot of that heat just goes down the drain with the water.

I never considered an electric furnace - I come from a land of ice and snow and the only real option is natural gas.

I live in a land of ice and snow and we rely entirely on mini-split heat pumps in the winter [1]. Admittedly they do lose efficiency quickly when temps drop well below freezing, but they work well enough here.

I have also seen some pretty cool looking "passive" houses that, due to excellent insulation, are able to heat the entire house with a 3kW furnace [2]. And these are in very cold locations (e.g. Alberta, Canada).

Electric heating is the future!

[1] https://learn.compactappliance.com/mini-split-heat-pumps/

[2] https://www.youtube.com/watch?v=AlA4_lesrU4

I live in Alberta - I love the idea of a passively heated house, but for now I'll stick with my 25 kW (converted from BTU) gas furnace. It's about 5 cents / kW for electricity and 0.5 cents for natural gas. That house would still cost more to heat. Sadly natural gas has a carbon footprint by default.

What you want is not an "electric furnace", which uses electrical heating elements, but a heat pump per one of the other replies.

Mitsubishi has some that can extract heat from the outside air even down to -30C.

Most though only work down to about +5C (they're used in more temperate climates). So check the specs.

They also work for AC.

The highest BTU heat pump I see is 46,000 - that's not going to be a solution for a lot of homes, which need 30,000 / 1000 sq ft, not to mention loss in efficiency as the heat drops so you're getting less than that when you need it the most.

How much you need to heat/cool a home is more of a function of its level of insulation and air tightness than its mechanical capacity.

It's possible to design house that need almost zero BTUs:

* https://en.wikipedia.org/wiki/Passive_house

When looking at bang-for-buck / value / ROI, better insulation and air sealing should be done first. If you can reduce the number of your blower door test, then you'll have to spend less on running capacity (and their related costs).

Passive houses are cool, but most houses aren't, and can't be retrofitted to fit the requirements.

True, but they show that comfort is possible without crazy mechanical power. Improve your insulation first, and you'll need less BTUs afterwards.

I really wish I'd read these comments and realised the experiment isn't finished before scrolling up and down the article for five minutes trying to find the conclusion.

> I really wish I'd read these comments and realised the experiment isn't finished before scrolling up and down the article for five minutes trying to find the conclusion.

Gwern.net has useful heading information on each page. This particular one says:

> modified: 13 Dec 2018; status: in progress;

Presumably the status tag will be modified to "draft" or "finished" once conclusions are available. https://www.gwern.net/About#confidence-tags

Gwern continues to be one of the most authentically curious and transparent researchers around. I highly recommend perusing his essays. Thank you and keep up the excellent output.

With every similar news I feel dumb. Because my parents and my grandparents used to say same things. It was easy to dismiss all the advice as grumbling, but I really should refresh air before sleeping, humidify air in heating season, eat more vegetables... etc. etc.

Not all of it was correct. My parents' generation "learned" to avoid eating fats to not become overweight. My grandmother knew that you shouldn't eat fresh bread before it cooled down (unhealthy or so).

We researched the latter recently and found out, that this idea was spread after the war so that the children would not eat too much of the freshly baken bread, because it tasted better. No health implications at all.

The problem is that parental figures previously based such general information on gut feelings, personal anecdotes and old wives tales. A lot of what parents say can be correct, but when there is a lack of information to fill the gaps to a childs understandable inquisitiveness it's filled with ignorance or scorn by the parents that are going through the motions who have no answer. It's an interesting dynamic with the resources available for information to the general public that it will be the children that can quash misconceptions perpetuated by parents. We all, including future generations, will become better parents for it.

I agree, but at the same time I feel that we are losing some of this common folk knowledge. It is strange, because we are in this information age, however it's full of noise. I'm not saying that it's bad to know how things are extensively with scientific rigor. It's good, but we are sometimes throwing the baby out with the bathwater.

My parents had limited vocabulary, but in a way they meant the same thing. Stale air (a hopefully faithful translation from my language) can have many meanings, but in context it means air with high CO2 concentration. I'm wondering how much of this is also the disconnect caused by fast technological progress and evolving language with it.

I thought the same. Rearing a newborn recently, I find that much of the parental/pre-parental advice works well. However, I just now realized, they probably actually understood the problems. But since only the advised actions stuck in my mind, without the problem analysis, I came to think they would act on gut feelings. I think this is sort of a child/grandchild bias.

This leaves aside parental scorn/ignorance as you describe it. Sounds like stressed-out parents, if I may say so. However, I don't know how future generations will get better at it, only that you may get better at it.

Drinking cold drinks in winter makes you cough.

Interesting, do you have an explanation for this?

Not the parent, but cold temperatures in the face/throat increase mucus production to protect your membranes, and excess mucus in the respiratory system will need be coughed up.

Of course it varies greatly depending on the person, temperature, state of immune system, humidity, etc.

But it's just the opposite of hot tea helping you cough less.

well it would have helped if they explained it or knew why. they just “felt” those things. if I knew it’s because co2 was building up and it can make you dizzy, i’d open the window

Fire safety experts recommend that bedroom doors be closed at night: https://closeyourdoor.org/

The fire safety song on that site is hilarious: https://www.youtube.com/watch?v=Uu9ReCQgvv4

That was way more entertaining than I expected. Shame they don't have many views.

Maybe they should change it to closeyourdoors-crackyourwindow.org instead...

Police recommand you close your windows to prevent breakins.

If you believe that is a serious concern in your area, get bars for your windows. There is no shame in it, I've lived in numerous buildings that had barred windows.

However I suspect that most people don't sleep on the ground floor (either in a multi-level house, or in an apartment building) so for them this should be less of a concern.

But the HOA won't let you and you'll have a hard time selling it then, because you have indicated that the house is in a dangerous area.

Well, is your area a dangerous area? None of the homes in high crime neighborhoods I've lived in have had HOAs.

But if you're actually contending with both at the same time, there are window bars that are placed inside the window, not outside.put the blinds between the window and the bars, then crack the window open and get some airflow.

Or hell, install a fan in your attic, the way people used to before AC was ubiquitous. Bedroom ventilation is not an unsolvable problem. If you really want a solution, you can find one. If you want an excuse to have no solution, I'm sure you can find endless excuses too.

Bars on the windows? Now we're back to fire safety.

Yes I considered that and I was curious, so I looked it up. It seems the federal government estimates a lower bound of 25 people injured or killed in fires due to bars on windows every year. All things considered, I think that's not so extreme, although the risk should be weighed against the relative risk you believe burglary poses in your neighborhood. 25 per year is several orders of magnitude lower than the number of victims of violent crime stemming from home invasion, although many neighborhoods will not embody those averages.



There are other solutions as well. Many window frames are designed to permit the window to be cracked open but not opened fully, to prevent ingress while still allowing egress (either by disengaging the mechanism or by breaking the window if necessary.) Such a mechanism can often be retrofitted to an existing window frame for no more than a few dollars. I've seen people create their own using a short length of dowel rod placed such that it prevents the window from opening fully. There are also a variety of purpose made mechanisms on the market.

These mechanisms are not as secure as bars on windows, but about as secure as a normally closed and locked window. The payoff for less security is enhanced aesthetics and fire safety.

There are many reasonable solutions to bedroom ventilation.

There's one big problem with this entire idea of co2 levels affecting sleep quality or humans in general:

Even though there are cognitive effects of CO2, most often the CO2 levels in indoor rooms are simply a sign of low oxygen levels. In fact, there should be an inverse relationship between CO2 and oxygen in rooms. So an experiments would need to take this into account and supply pure oxygen to make up for the oxygen that has been used up.

It should be noted though, that the effects of low oxygen are already very well known and well understood, thanks to decades of research funded by air and space agencies.

It should therefore be pretty easy for CO2 researchers to control the outcomes of their experiments against the known physiological effects of hypoxia, to determine what effects are actually caused by CO2.

And aside from that, the dosages being discussed here are far, far lower than would be a noticeable dent in the amount of oxygen in the atmosphere. 1000 ppm CO2, the lower bound of observed cognitive effects, is 0.1% CO2, way less than the point where hypoxia is known to cause problems. The atmosphere is 20.9% oxygen at sea level and while I am not an expert in the math of partial pressure, a decrease of atmospheric oxygen to 20.8% doesn't strike me as sufficient to explain the observed effects. That's a 0.4% decrease in the partial pressure of oxygen, or about the equivalent of a 300 foot increase in altitude, or taking an elevator to the 20th floor of a building, nowhere near enough increase in altitude to make you light-headed.

The symptoms of slight sub-clinical hypoxia are in line with the observed effects of people in high CO2 office rooms: headaches, concentration problems, tiredness, etc.

In a closed small room, the oxygen is mostly used up after a couple of days.

One person in a small tightly closed room will lower the oxygen level significantly, by 5-10% (consumption is around 20 cubic feet, and a small room has about 200 cubic feet oxygen in volume in total)

CO2 and oxygen work in tandem in the human body, and studies in the medical field have shown that an increase in carbon dioxide increases breathing rate, breathing volume, heart rate and metabolic rate.

The result is an increased need for oxygen, which will not be met in a closed room.

Thus I speculate that an increase in CO2 with an accompanying increase in oxygen (or at least a stable flow) will mostly negate the observed symptoms.

My preliminary working theory would be that the previously observed effects from high CO2 in rooms (office rooms for example) are due to the interaction of both high CO2 and low O2.

That's intuitively appealing but when you look at the numbers it's almost certainly false. When CO2 goes from 400 ppm to 1000 ppm then oxygen will go from 21000 ppm to 20400 ppm, a 3% drop which isn't going to be enough to change anything.

No, the body does not use the same amount of oxygen, as the amount of CO2 it exhales.

The amount of oxygen used is way higher.

A person consumes 19 cubic feet of oxygen a day.

Edit: I looked at the composition of inhaled and exhaled air, and now I realize the reason O2 is being taken out of the air in higher amounts than CO2 is introduced, is that the exhaled amount of carbon dioxide is not the total amount of carbon dioxide that has been created in the body.

When the CO2 in the room gets higher, more CO2 is actually taken up again from the room back into the human body, with the exhale rate staying relatively constant. Or in other words, a significant part of the increase in CO2 in the system human <-> room is actually in the human, not in the room. The room measurement thus covers only a part of the CO2 being produced in total, and only the unknown total amount of CO2 produced reflects the totality of O2 being used up.

This means a change of 1000 ppm of CO2 in the air will mean a higher amount of oxygen has been used up.

Oxygen is 21% of the atmosphere, so 210000 ppm, not 21000 ppm.

Good observation. That said, co2 and o2 should move pretty much in tandem if the source of high co2 is human breathing + limited ventilation, right?

This could potentially account for why no ill effects of high co2 were found in submarines. Presumably o2 supply there is well maintained.

Do household air quality standards include o2 levels?

Most of the CO2 stays in the body, which ultimately means that significantly more O2 is used up than CO2 is introduced back into the air again.

The comment about submarines is highly interesting to me, I will look into the studies! If you have any sources about that to share, I would love to read them.

They do move in tandem on a molar basis, but because there is so much more O2 in the air, even very high concentrations of CO2 have barely changed the concentration of O2.

They probably do not move in direct tandem, because most of the CO2 stays in the body, which means a higher amount of oxygen is taken out of the air, then CO2 being reintroduced to it.

Every time you breathe in, you not only breath in O2, but also CO2, thus lowering the amount of CO2 in the room relatively to the amount of oxygen.

In other words, 1000 ppm CO2 in the air do not mean 1000 ppm O2 less, but significantly more parts of oxygen less.

> because most of the CO2 stays in the body

Say what?

... not at all. No CO2 is "stored", though it may temporarily hang out in buffers such as the blood. But they have a very limited capacity and the flow out is extremely close to the production on a very very short timescale, and on a longer timescale approaches equality.

> which means a higher amount of oxygen is taken out of the air, then CO2 being reintroduced to it.

This is true, and I was wrong in my comment, but not for that reason. Only some of the O2 used is paired with CO2 and breathed out. Some joins with hydrogen from foods and becomes water. Most foods are carbon chains, with each carbon atom having two hydrogen atoms, so this ratio can get as high as around 2:1 for low-oxygen foods like fat, but lower for carbs, which tend to have significant quantities of oxygen (which will in balance add to the O2, meaning that more of what is used up when breathed in is breathed out). (Proteins also have nitrogen which complicates things.)

Right, so then in a single night in a poorly ventilated room, a human would not breathe up enough of the O2 to make any difference in their functioning?

(Meaning we could rule it out as an explanation for the effects, if the effects do exist)

Previous company I worked for had dashboards and Slack integration for the CO2 levels on all floors. There's a blogpost on how it was done (Raspberry PI's, CO2 sensors and open-source python script): https://blog.wooga.com/woogas-office-weather-wow-67e24a5338

In Japan, the building code requires every room to have an air vent [1]. Initially I was skeptical of them and was looking to close them to save on heating costs in the winter. But after doing a little research, I decided they are probably best left open to reduce condensation and mold growth.

Now I'm curious how effective they are at keeping down CO2 levels at night. I would like to try this experiment in my house.

[1] https://resources.realestate.co.jp/living/japanese-apartment...

There are regulations[1] in the UK too.

We've had new UPVC windows installed over the past few years and they've all got hidden 'trickle' vents.

[1] https://www.gov.uk/government/publications/ventilation-appro...

FWIW, I have almost no dream recall, and am not as rested, when the window is sealed shut. We are four humans and two cats (usually) in a small-ish bedroom, creating a lot of co2. There is built-in ventilation in each room, but performance starts declining 2 weeks after every filter change (which cost €20). So I swap the filter only once every 1-2 months, and instead open the window ever so slightly (moving the lever just a bit towards open position, weakening the seal). Voila, perfect dream recall and much better rested the day after.

I live in a tropical country and I always prefer to sleep with open Windows. The only problem is the noise. I believe noise affects the sleep quality as much as well. Earplugs might be a solution but I don’t know any good brand which are comfortable enough for long time carrying.

It seems there will soon be a mass market solution: https://www.haaretz.com/israel-news/business/sick-of-the-noi...

This has all the markings of a pseudoscientific fad.

1. Abundance of flimsy anecdotal evidence

2. Mostly subjective measures of outcome (I feel smarter and refreshed!)

3. Seemingly plausible, but totally unverified scientific reasoning

I'm not holding my breath yet.

This might be completely unrelated, but let's give it a shot:

I've noticed that sometimes after spending extended periods of time (in the magnitude of hours) in very close proximity with a significant other (e.g. cuddling, kissing, etc.), I feel groggy, dizzy, and have brain fog/difficulty focusing.

Could this be related to CO2 levels? I've been feeling it today and was wondering if it is hormone related, but CO2 could be an interesting explanation as well - I have noticed my breathing tends to slow down during these times as well.

I've never heard anyone else describe this so if you have any similar experiences, please share so I don't feel so alone with this.

There's a lot going on physiologically when you're getting intimate (e.g. oxytocin, testosterone), so it's hard to tell. However, I've noticed the same thing, and I'll also add a loss of appetite.

Glad someone can relate, but sorry you have to deal with it as well.

What are your thoughts on seeing an endocrinologist about this? In addition to oxytocin, testosterone, etc., I was also wondering if it might be related to prolactin levels.

I also just read some people talk about similar symptoms here but no clear answers: https://patient.info/forums/discuss/partner-becomes-ill-afte...

I had that happening. For me it was an allergic reaction which slightly blocked my sinuses and reduced the air intake. The allergy was previously undetected because I do/did not use the same cosmetic products that my partner uses. A antihistamine nasal spray may help, but check with an ENT.

Interesting, so does that fall under the category of "mild hypoxia" or something?

Is it just coincidence that Tom Scott uploaded a video about CO2 and its influences at almost the exact time the gwerns link was submitted?


Wasn't there a recent discussion on HN on the Baader-Meinhof Phenomenon?

It appears it has become pretty fashionable to mention it, it’s probably the next ‘skeuomorphic’.

I'm eager to hear the results. I recently got an Awair 2.0 after seeing this talk by DHH: https://www.youtube.com/watch?v=MRqh8oLY7Ik

It quickly confirmed that, without turning my thermostat fan to "ON", my bedroom CO2 jumps from about 1000 ppm to 2000 ppm within a couple hours of us going to sleep.

In the fall, my wife and I started waking up in the middle of the night feeling like we couldn't breathe. What I figured out is that the neither the heat nor cooling was running because the weather was pretty much perfect. We have to keep the door closed because our cat will swat at us in the middle of the night otherwise. I figured there would naturally be enough of a draft to not make this a concern and it's a fairly large connected master bedroom/bathroom with high ceilings to hold a lot of air, but I guess that isn't enough. So that's when I learned about the "fan" function on my thermostat.... never had a need for it in my life.

Now I just need to figure out how to get lower than 1000 ppm, which is already a hit against cognitive function. Our house has no screens currently and even if we install some, it's not like I want to have windows open in the middle of winter. I've heard house plants don't have a huge effect, but I'm willing to try.

If the human race gets to 5-6C of warming, the entire outside will have about 1000ppm of CO2. At 4C, about 800ppm outside, perhaps by 2100. https://www.co2.earth/2100-projections

My kids may well see stuffy room CO2 levels outside within their lifetimes.

You'd need hundreds of houseplants to mitigate the co2 created by one person completely, I am not sure if a few would be better than nothing.

There are more variables at play than just co2, humans are not perfectly elastic spherical CO2 emitters ;)

https://en.wikipedia.org/wiki/NASA_Clean_Air_Study https://www.apa.org/monitor/apr01/greengood.aspx

Do you know a chart of how fast a plant turns over carbon dioxide? I'm trying to search, but the results are mostly global warming related.

It varies by plant type, health, and other factors. So it's hard to be specific.


>back-of-an-envelope calculations suggest you’d need around 400 houseplant-sized plants.

Or you can grow spirulina or other microalgae which is much more efficient at converting CO2, and at absorbing the available sunlight. I believe you need about 5 m2 of southern facing window in a bioreactor that is 6 inches deep to convert the 1 kg of CO2 that a person creates. Can't find the citation sadly.

I'm casually experimenting with this too, to improve AQ in my home office. Do you recall the surface area in the 6-inch-deep bioreactor (or total volume)? The only hard numbers I've found are from the Russian BIOS-1,2,3 experiments, which suggest 18L/person of Chlorella will 75-100% compensate for a person's CO2.

I have 18L of Spirulina, which appears to be having some effect, though not anywhere near a complete offset. Though, my setup is quite sub-optimal, and I've seen articles that suggest Chlorella is a couple times more efficient at biofixation than Spirulina. Continuing to tinker :)

Install an air exchanger. Panasonic makes some that are reasonably priced.

They're called energy recovery ventilators or ERVs. The Panasonic units are most well-regarded.

Do these need to be a whole house system or can they be installed just in one room?

Reading reviews of the Awair, seems that many people complain that the measurements are not accurate or consistent with other measurements... can you speak to that at all?

I can't really. I don't have other sensors besides the temperature matching what the thermostat says.

In the talk I linked, DHH said he had tried dozens of other sensors and found this one surprisingly accurate for the price point. He did mention the temperature and humidity readings were not as accurate as he expected since sensors for those are so cheap, but that's not really why I got one.

Our HVAC system has a “circulate” option that we sometimes keep on. It turns the variable speed blower on the lowest setting a few times per hour and keeps air flowing well.

Yeah, we have a Nest in our house and I have it set to circulate the air for 15 minutes out of every hour.

We started running it like that only at night as we found that the bedroom would get pretty warm during the summer while the center of the house (where the thermostat was) would stay nice and cool, but after running it like that for a bit, decided to just let that routine run all 24 hours of the day since it equalizes temperatures so well across the whole house.

Wow, I never realized that this would help equalize temps through the house. Our bedroom gets so hot when 2 people sleep in it at night. I have been considering putting a vent in the wall above the door so heat could escape to the rest of the house.

Though all this time, I thought it was just the heat. I wonder if the CO2 levels are also what is keeping me waking up at 4-5am every day...

I'm going to try this circulation trick with my Nest now and see how it goes.

It works fantastically!

At first I was worried about the extra electricity usage or the extra wear and tear on the HVAC system, but after trying it at the recommendation of a neighbor, I've been nothing but happy, and I haven't noticed any change in my electricity bill so there's no worries there.

Have you thought about installing a screen door in your bedroom? You could also look into reinforcing it with chicken wire or hail cloth to keep the cat out.

Scott Alexander (slatestarcodex) provided a meta-study and also described how reducing CO2 in his cottage reduced headaches, fatigue, and poor sleep: https://slatestarcodex.com/2018/08/23/carbon-dioxide-an-open...

After reading this, I got a Netatmo CO2 monitor like Scott and Gwern. I found that CO2 peaked in my bedroom at around 1500 PPM at 6 AM with the door closed and that I could keep it under 500 PPM with the door open or a window open.

Scott Alexander also suggests getting around 10 succulents, if you don't want to open a door or a window.

Edit: Scott Alexander also published these survey results from other people who experimented with reducing CO2 in their homes: https://slatestarcodex.com/2018/10/04/nighttime-ventilation-...

How big should these 10 succulents be?

”But if one room can mix with and increase the Netatmo’s room all the way up to 1934PPM, what must the original concentration have been like?”

Why not move the weather station to the bedroom for a couple of nights? (And make sure the sensor is at nose/mouth height, preferably close to it. CO2 is heavier than air, so concentrations may be higher closer to the floor in a closed room with little movement)

I would also do a back-of-the-envelope computation along the lines of https://www.globe.gov/explore-science/scientists-blog/archiv... or https://ac.els-cdn.com/S1877705813007558/1-s2.0-S18777058130..., to verify the numbers the weather station produces.

And the lesson of all this seems to be: get a large bedroom and leave the door open (both easier for the well-off, so get rich parents!)

> CO2 is heavier than air, so concentrations may be higher closer to the floor in a closed room with little movement

How significant is the gradient? Would it make a noticeable exposure difference to sleep in a high bed versus a mattress on the floor?

"Why not move the weather station to the bedroom for a couple of nights?"

which he did, not too far further into the article?

Oops. I thought I skimmed the text well enough to detect that, but apparently was looking too much for the graph “CO2 concentration over time during the night” that to me, seemed obvious as the thing that had to be there.

For the hackers out there, you can record CO2 with a K33 sensor. The [0] Livpi uses this chip.

EDIT: it appears the Livpi uses a K30 chip. The K33 [1] is the version sold on industrial sites.

[0] http://www.livpi.com/ [1] https://www.co2meter.com/products/k-33-icb-co2-sensor

Went looking for devices for the bedroom, but ran into an article about plants that might help in that setting:


Most plants actually use oxygen at night and will increase the level of CO2 while you sleep. The exceptions will be plants that use the CAM pathway [0] - succulents mostly.

0. https://en.wikipedia.org/wiki/Crassulacean_acid_metabolism

Those scrub the air of pollutants. No way they lower co2 sufficiently though. Plants reduce co2 by growing. Which they do....slowly. By contrast a human will spike the air in a room quickly by breathing.

That's interesting, I was just linking the article because it was talking specifically about co2 and NASA recommendations. In fairness, it didn't give any hard numbers on what to expect.

I think the author of the piece just made a poor inference. Air cleaning isn't necessarily the same as lowering co2.

That said, seems there are some succulents that do most of their co2 intake at night. Those would work best for co2. But you would need....at least 30-40 of them.

Opening a window, by contrast, works extremely well, and quickly. However, this requires non-polluted outside air. Else you're exchanging lower co2 for pollutants.


Opening a window is just a bit too expensive in the -20 degree weather we're getting around here right now :-)

I don't think a tiny crack makes that much difference. I also live in a -20 area. Also the colder it is, the easier venting happens, so a small crack has the same effect as having the window open much more in summer.

I can't remember the total, but I recall seeing a calculation about this and it didn't amount to very much energy, especially if the bedroom heat isn't on super high.

Anecdotal, but I've heard the Germans often tend to keep a window open a bit year round, and I know my grandma did even in winter. She was pretty frugal too.

Air out with windows wide open for 5 minutes a couple of times a day. The air will cool down, but your furniture and walls will not cool down, so the air will quickly warm up again.

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