
Build a do-it-yourself home air purifier for about $25 - io_io
https://www.uofmhealth.org/news/sinus-hepa-0630
======
benbojangles
I built my own air purifier in 2016, living in London, I was living in a
basement and was having breathing problems due to mould. My landlady was
gaslighting me at the time, so I built the air purifier. It worked for a while
but mould spores cling to the paper filter and eventually grow into the filter
material. I think Dyson uses glass fiber filter to stop this problem. My
filter helped a lot, but eventually I had sclerosis infection on my brain and
ended up in hospital with lung infection and brain lesion, still recovering
after two years, and I will never be my old self again. I was subletting so
had no grounds for complaint, I had to choose between homelessness or phoning
a distant relative I hadn't spoken to for 24years, I chose the latter and I
think it's the reason I'm still here.

~~~
electic
Woah, this is pretty scary. Thank you for sharing. How did you know it was
mold that was in the air? Is there some sort of test kit that you can buy to
test for this. Mold is pretty hard to detect because you can't really see it
because it typically hides between the walls.

Any advice appreciated.

~~~
fyfy18
The CDC has some recommendations on it (yes you can have mold tested to see if
it's dangerous):

[https://www.cdc.gov/mold/stachy.htm](https://www.cdc.gov/mold/stachy.htm)

I'm not really sure about keeping the humidity below 50% though. The UK and
most of Northern Europe has rather high humidity in the winter. It commonly
reaches 80-90 RH outside, so you'd have to heat your house to 25c/77F to bring
the humidity below 50%.

~~~
roel_v
"The UK and most of Northern Europe has rather high humidity in the winter."

Indoors? No, not at all. In the winter the temperature in my house/office is
21-22C and 17 at the lowest at night, and I have to run a _humidifier_ 24/7 to
keep the humidity over 30% (otherwise the wooding floors shrink too much).

~~~
zimpenfish
(anecdata but...)

Currently in the bedroom (thanks Netatmo) it's 17.8° and 69% humidity (with
one of the three windows open about 0.5"). That compares to 14.0° and 78% on
the balcony. Looking at the graphs, 50% is the lowest indoor humidity over the
last month.

~~~
roel_v
Yes, bedrooms have the windows open more often, and usually less/no heating.
How many hours a day do you have the windows open? Is there a heating source
on or nearby? If you close the window, you'll see RH drop quite fast (in most
houses). I'm going to try this same experiment tomorrow, I'm quite interested
to know.

Still - mold in houses is not a problem in houses in Western/Northern Europe,
except for the most pathological cases (for example, mold scores you iirc 2
points in Belgium on the 'uninhabitable property' test, where 9 gets your
building declared unfit for living in. Having small holes in the roof or small
cracks in the walls (still structural defects) gets you 3. That's how unusual
mold is around here. OTOH when I lived in New Zealand, mold was met with 'eh,
there's bleach in isle 5 at Countdown, just wipe it down.'. I was like 'wut?'.

~~~
zimpenfish
> If you close the window, you'll see RH drop quite fast (in most houses).

Alas, it does not, but that's possibly because other windows are open around
the place and there's relatively good airflow.

> I'm going to try this same experiment tomorrow, I'm quite interested to
> know.

I'll see how it goes tomorrow with the window closed and various doors closed
to minimise the effect of the other windows.

------
peferron
Important tip: if you set up an air purifier in your home, make sure to plug
all drafts around your house: windows, doors, etc. Even a DIY purifier with
small airflow can make your indoor air excellent if given enough time to do so
and no leaks to fight against.

If you want to get some fresh air in your home, do not leave a window half-
open all day long—instead, open all your windows at once to cycle the air as
fast as possible, then close them again and let the purifier do its job. If
you do that in the morning (ideally just before leaving, if you aren't staying
home), you'll have great air quality through the entire evening and night.

Since we're on HN, I'll also mention a toy project I built a while back [0].
It uses a Raspberry Pi to read particulate matter sensor mesurements over
serial link from a Dylos 1100 Pro, then pipes it into Redis and InfluxDB and
ultimately Grafana for presentation. I've used it to track the air quality in
my home in for the past year or so and it's pretty fun. In my case, cooking is
usually the biggest contributor to poor indoor air quality!

[0] [https://github.com/peferron/air-quality](https://github.com/peferron/air-
quality)

~~~
heybrendan
Very interesting!

How does the Dylos 1100 Pro compare to, for example, the Nova SDS011 sensor?
By my cursory review, the SDS011 is much cheaper and appears to offer a more
native Raspberry Pi-compatibility experience.

Is the Dylos more precise? Can it produce readings the SDS011 can't? Are the
two sensors measuring fundamentally different things?

Finally, if you had to do it all over again, would you choose a different
sensor or stick with the Dylos?

Thanks for sharing your project and for your insights!

~~~
misev
SDS011 is the basis for luftdaten.info; have a look here for a diy guide
(optionally including humidity/temperature as well):
[https://luftdaten.info/en/construction-
manual/](https://luftdaten.info/en/construction-manual/)

~~~
imarg
Hi, this is an interesting project. It seems to be targeted for outdoor
measurements. Do you know if this also suitable for indoor measurements
(meaning if you want something for indoor air quality, would you measure the
same things?)

I recently watched a video from dhh
([https://youtu.be/MRqh8oLY7Ik](https://youtu.be/MRqh8oLY7Ik)) about air
quality at home and was thinking if there was a nice diy solution for
measuring it.

------
leon_sbt
Generally there are two classes of objects that you want to filter for.

Particulates and VOC (Volatile Organic Compounds). Think of particulates as
specs of dust with varying size and VOC's as random chemical compounds such as
spray paint, smoke, oders.

The general go-to clean room/industrial filter stack is Prefilter(F5
Bag)->HEPA->Activated Carbon. The pre-filter catches all the big particulates
to prevents clogging the HEPA filter. The HEPA filter catches all of the
really small particulates. The activated carbon captures most of the
VOC's/oder/smoke.

The official way to monitor when a particulate filter is bad, is to measure
the pressure drop across the filter, and compare to manufacture specs. For the
carbon filters, you would install a gas sensor measuring whatever chemical
your trying to scrub. When there is a spike in that particular gas compound
from your sensor. You know the carbon filter is saturated, and should be
changed.

It looks like the the filter mentioned in the article video,combines all the
filter products into a single product. Nice! If your air handler can manage
the increased pressure drops, please buy the most legit filters you can buy.
It's literally the cheapest insurance you can buy.

~~~
clairity
> “The general go-to clean room/industrial filter stack is Prefilter(F5
> Bag)->HEPA->Activated Carbon.”

yup, i bought a blueair 211+ ([https://www.blueair.com/us/blue/blue-
pure-211/1695.html](https://www.blueair.com/us/blue/blue-pure-211/1695.html)),
that has exactly those filter elements in a nice (if bigger than expected)
package. this model was recommended by both consumer reports and the
wirecutter (until recently, cynically thinking they didn’t pay wirecutter’s
“endorsement fees”). it’s effectively eliminated my constant coughing,
sneezing and runny noses before i got it.

~~~
MarkMc
I just bought the same model. What makes it so effective is that it has a
filter on four large sides so it can process a large volume of air very
quickly.

~~~
chaostheory
Does it spew out ozone? My memory may be off but I remember this model not
meeting CA air purifier standards which was why Amazon couldn’t ship it to me

~~~
clairity
no, there is no ozone generator in this model (usually that's done using
electrostatic plates).

~~~
chaostheory
I'm still curious then as to why this specific unit doesn't meet California
air purifier standards, which is why Amazon won't sell it to me.

~~~
clairity
i'm not sure. i live in california and bought mine on amazon. wish i could be
more helpful!

------
LeoPanthera
Huh! I independently "invented" this myself a couple of days ago when the Camp
Fire blanketed the bay area in smoke. I got a 20x20 filter and some duct tape
from Home Depot and a box fan from Target. (After discovering that Home Depot
only sells fans in the summer.)

I don't think I was the only one, though. HD was doing a brisk trade in 20x20
filters, and I think I bought the last box fan at any Target in the entire bay
area.

My "creation":
[https://i.imgur.com/jeJfqeW.jpg](https://i.imgur.com/jeJfqeW.jpg)

~~~
matt-attack
Don't you want the filter on the incoming side? Air handling systems always
put the filter on the inlet as far as I'm aware.

~~~
sbradford26
The main reason why furnaces and cars have it on the incoming side is because
the dust and particulate can damage the engine/blower. So you want to filter
it out before it reaches there. In a system like this, the box fan will not be
damaged by the particulate so you can instead push the air through the filter
instead of pull it.

------
abalone
Can we talk about Molekule? Their team and some SF tech community folks have
been plugging it all over Twitter during this tragic wildfire crisis. But it
seems like snake oil to me. It’s $800. Certainly for smoke particles it can’t
possibly offer any more protection than a standard HEPA filter. But even for
its claimed ability to nuke VOCs, the claim seems ridiculous. While particles
can deterioriate under prolonged exposure, the airflow must be too high and
the exposure too short to make much of a difference.

What gets me is how these guys misuse “science marketing” to play on people’s
fears about germs. Add the shameless exploitation of a real tragedy here.

~~~
chaostheory
I had one. It has multiple issues:

1\. CADR is really low to the point where the unit is near useless due to #2

2\. In addition to a low CADR, it has the highest noise. It looks and sounds
like a jet engine when you have this thing on high, which is needed due to the
low CADR. This is the loudest air purifier that I’ve ever owned

3\. If you get a defective main filter, the unit will emit an unpleasant
metallic smell. I haven’t tested the particles yet but I doubt the air is
clean.

4\. Unlike other smart air cleaners in the same price range, it’s app and
smart features don’t work. You can’t even create a schedule for it

It’s a very flawed device

~~~
chaostheory
Forgot

5\. The unit works using some LED light. A. it is bright B. It is not
replaceable. Meaning after 2-4 years of operation, the unit becomes a
throwaway. This is not a good thing for a unit that costs over $700

------
akeck
Note that restricting airflow on a radial fan can cause the motor to heat up.
Make sure you get a 20-inch fan with a fuse. To reduce heat, increase air flow
by making a box with three filters and by using 2 inch deep filters. Also,
when I built my three filter "box" last fall, I was able to order a set of
three MERV-13 20x20x2 filters directly from Nordic Pure for less than what
they cost on Amazon. Finally, to make a cube, cut the remaining sides from the
filter box. Then roughly tape it together with small pieces of duct tape. When
the filters and panels are in the right spots, seal it completely with duct
tape. Remember to put the box of filters on the "pull" side of the fan with
right sides of the filters facing outwards.

~~~
sgc
I agree with placing the filters on the pull side, since that is what all hvac
units do and what the filters are designed for. To be effective, you are also
corrected that a deeper pleated filter with more surface area is the only way
to go. But I am unconvinced the motor will heat up. Certainly there will be
less air so if it is air cooled it will heat up from that, but at the same
time, a fan in a partial vacuum uses less energy and should heat up less. Just
slap a meter on it and you will see the draw can be significantly lower, since
it is doing less work.

~~~
meesterdude
to perhaps reinforce your point: I put a filter on the front (as in this
video) and the fan died a few weeks later.

------
Dave_Rosenthal
I spent the weekend researching, implementing, etc. air filtration as one of
those affected by the CA fires. It was worth it!

The first step for me was getting a device to measure particles in the air.
The air quality index (AQI) is an aggregate score that is made up of
contributions from several harmful components. Of these, the quantity
(weight/volume) of small particles (<2.5um) is often the large contributor.
This is called the PM2.5.

Directly measuring PM2.5 is very hard, requiring a device that eliminates the
larger particles from the air (typically a cyclonic separator it seems)
combined with some way of capturing and weighing of the very small quantity of
remaining particles (we're talking ug/m^3).

Many home air quality sensors instead measure the count/volume of particles
_larger_ than 2.5 um and call that the "2.5um measurement". You can see the
problem. I bought a laser particle counted called Dylos DC1100 Pro. The Dylos
measures particles counts larger than 2.5um as is common, but also counts
particles larger than 0.5um. Of these two numbers, the 2.5 count is only
vaguely correlated with the actual PM2.5 measure, but the 0.5um count is
highly correlated.

A bit of internet research (it seems many people have used the Dylos meter in
various projects) and I was able to construct a scale to correlate 0.5um+
counts to PM2.5, and therefore AQI. (0.005*count~=ug/m^3)

OK, all that done, to the filtration. First, I installed 3M 1550 MPR furnace
filters (~MERV11). The "1550" is a measure invented by 3M
'MicroParticleRating' (or something) and is supposed to speak to how well the
filters remove small particles. However these furnace filters don't really
knock down very small particle counts in once pass. Sure enough, putting the
particle meter at an air duct, the large (2.5+) particle count was way down,
but the small particle count was only down a little bit (15-25%?) from the
ambient air. Net effect is that after running for several days my house
numbers are about 1/3 of the outside air counts.

I also bought a BlueAir HEPA filter for my bedrooms. HEPA is supposed to be
99+% effective for particles 0.3um and up. This filter is in a whole different
league. The particle counter placed on top of the filter returns near-zero
small particle counts and does a much better job eliminating smells. The room
they were in got down to 1/10 of outside levels.

Overall I'm glad I got both types of filters, we are sleeping better, and the
meter was very helpful to understand what was going on.

~~~
Kadin
Did you put the filter on the intake or outflow side of the fan?

I have built one of these (20x20 furnace filter on a box fan) and always put
the filter on the intake side of the fan. However it seems like people are
placing the filters on the outflow side of the fan instead, for reasons that
are not clear.

Since it seems like you did some measurements, do you have any idea whether
it's preferable to have the filter on the intake or outflow side of the fan?
(I note that in furnaces and other air handling equipment, filters are almost
universally on the intake, not the outflow, side, presumably because this
keeps dust out of the blower/heating mechanicals.)

~~~
sgc
when you place it on the intake, it is sucked against whatever you are using
to stop it pulling into the fan, if it is on the outtake, it can bubble out on
the edges and the air can escape rather than pass through the filter. Intake
is the only correct solution for these homemade devices without a metal
diaphram.

------
apo
Nifty idea, but I'm not sure I agree with the technique used to prove
effectiveness:

[https://www.youtube.com/watch?v=kH5APw_SLUU](https://www.youtube.com/watch?v=kH5APw_SLUU)

The narrator puts a particle counter in front of the fan and notes the 90%
reduction. So far so good.

The problem is extrapolating this result to the entire room. Yes, maybe you'd
get close to 90% if the device were allowed to run a few days.

On the other hand, it could leave the situation worse (by blowing existing
particulates around) or unimproved (by failing to filter room air efficiently
enough.

Either way, I'd like to see see a controlled study. Two identical rooms with
identical usage. One gets a homemade filter. The other gets just a fan of the
same make and model, maybe with a dummy filter to baffle airflow.

What's the average particle count in both rooms after, say one week?

~~~
CompelTechnic
If you check out Matthias wandel's YouTube channel, he does some experiments
with hours-long recording of room particle counts. This is in a woodshop
(sawdust) setting with a similar diy filter setup.

------
adamwong246
I do this and it works wonders if you have pets. Tips: \- run this homemade
air purifier when you are vacuuming, as that tends to agitate particulates a
lot \- get 2 filters, a cheap low grade and a premium, high-HEPA-rated filter.
Stack them together and you can replace the cheap one frequently and the
expensive one less frequently.

~~~
zacharycohn
Does it go:

Fan --> Cheap Filter --> Expensive Filter

Fan --> Expensive Filter --> Cheap Filter

Cheap Filter --> Expensive Filter --> Fan

Expensive Filter --> Cheap Filter --> Fan

?

~~~
linschn
Cheap Filter --> Expensive Filter --> Fan

You put the filters on the intake, so that the airflow helps making a seal
instead of creating leaks.

You put the cheap filter first everything that it catches will not clog the
expansive one.

------
ed_balls
I wonder if you'd put cotton wool, how effective it would be. Here is my set
up:

\- I bought XIAOMI Mi Air Purifier 2 straight from China for $137.00 and spent
1 euro on a EU plug. It's so quiet that I can sleep next to it, looks nice and
it's quite compact, so doesn't take up much space. It has a particle detector
to adjust the fan speed. The app is useless, so a cheaper version without WiFi
and bluetooth would be great.

\- Buy some HEPA filters to put into window ventilation. You may want to
remove some plastic inside to increase the flow
[http://img.archiexpo.com/images_ae/photo-g/69621-5895915.jpg](http://img.archiexpo.com/images_ae/photo-g/69621-5895915.jpg)

\- Buy roomba like vacuum cleaner
[https://www.goodcheapandfast.com/articles/best-robot-
vacuums](https://www.goodcheapandfast.com/articles/best-robot-vacuums)

It will cost you less than 500$ to buy these and about 55$/year for new
filters. It is worth the money. The air quality is much better (I'm allergic
and I haven't had any problem with my sinus since).

What is more, is it worth it. It will save you time cleaning your place (about
10h/year)

Anyone has tried robot vacuums with mop or automatic dirt disposal function?

~~~
blattimwind
> I wonder if you'd put cotton wool, how effective it would be.

Not very. Wet wool is better, but only as long as its wet and clean.

> XIAOMI Mi Air Purifier 2 straight from China

Interesting question. Does the removal of particulates offset the health
impact of its cheap plastics?

~~~
csours
Does anyone know what the actual smell of "chinesium" comes from? The smell of
artificial rubber products from china, like remelt and cancer.

~~~
HillaryBriss
I bought a mechanical product like that one time and had to leave it outside
for about a month before it off gassed completely

~~~
reaperducer
Happened to me, too. Once with a dog house, and again with a set of car floor
mats. The floor mats are still out there.

------
CarVac
I made a custom wooden computer case with 8 120mm fans and a furnace filter
over the intake. The computer side is positive pressure and is as clean as the
day I built it 4 years ago.

I buy filters in bulk from McMaster Carr for $5 apiece.

~~~
rsync
Mcmaster carr[1] is a wonderful commerce website and I am so happy I found
them. I buy all of my fittings and hoses and so on from them.

[1] [https://www.mcmaster.com/](https://www.mcmaster.com/)

------
egghat
Check out the blog

[http://particlecounting.tumblr.com/](http://particlecounting.tumblr.com/)

The writer has tested a lot of combinations of fans and filters (Simple, HEPA,
Activated Charcoal). It's astonishingly easy to build a combination that costs
_way_ less than a "professional" Air filter.

The writer has put his findings into a "social startup" that builts these
simple, but very effective airfilters in some developing countries:

[https://smartairfilters.com/cn/en/product-category/diy-
air-p...](https://smartairfilters.com/cn/en/product-category/diy-air-
purifiers/)

~~~
hermosa
I use the SmartAir filter setup in Shanghai. It works great and the founder's
blog is very useful. I'm glad to support the project.

------
samsolomon
If anyone is looking for general air purifier recommendations. I'm a huge fan
of Coway systems.

I have pretty bad allergies purchased a Coway Airmega 300 for my 850sq ft
studio. I've had it for about 6 months and been incredibly happy with it. I
wrote some initial thoughts about it here.

[https://productdork.com/t/coway-
airmega-300-vs-400/56](https://productdork.com/t/coway-airmega-300-vs-400/56)

It has to be the best looking air filter on the market—I wanted something that
would look good in my place when I have people over. Beyond that it is
extremely well designed and the pre-filters are super easy to clean. I got
mine on sale for about $400.

For smaller rooms the Coway mighty is a better and more affordable pick. It
doesn't look as nice, but it is currently at the top of The Wirecutter's air
purifier recommendations. You can find it on sale for around $180.

[https://thewirecutter.com/reviews/best-air-
purifier/](https://thewirecutter.com/reviews/best-air-purifier/)

~~~
elektor
I have 2 of the $180 Coways and so far am pleased with them.

Once in a while, I will light a candle and when I blow it out, will hear the
air purifier go on full-blast (Speed 3) to clear the air.

Interestingly, it sometimes turns to medium power (Speed 2) when I'm just
shuffling around the room. I imagine its because I have a few rugs and its
pushing up a lot of dust.

------
wenc
I wonder: if one is generally healthy and the air quality is unproblematic,
should one get an air filter? Does air filtration potentially lower long term
immunity and make us less tolerant to particulates?

I worry about the long term effects of being “too clean”, that is, I think
there’s something to hygiene theory of disease. The body needs small stressors
and perturbations in order to thrive.

~~~
hourislate
I wouldn't worry about this if you live in a city. The amount of vehicle
exhaust, brake dust, and just general stuff in the air will make up for and
most likely counter the time you spend in a clean breathing environment.

------
valarauca1
I built a similar model over the weekend:
[https://twitter.com/valarauca1/status/1061362369702445056](https://twitter.com/valarauca1/status/1061362369702445056)

Used an existing box fan. I had to buy duct tape ($3) and the filter I used
one rated for 0.1micron pollen and viruses cost me $17 (rounding up after
tax). I cut up a plastic safeway bag to make the seal around it. Seeing as
most smoke particles is around 2.5-.5 micron I figured it'd be okay.

I threw this together at about 7am on Saturday after I woke up coughing my
lungs out at 6am (I live in the bay area). Just a quick trip down the the
Homeless Despot to get the parts and throw it together.

All things consider it works great. The air in my apartment is easy to breath,
but if I leave without a respirator (even today) I cough uncontrollably.

\---

As of Tuesday evening it has been running for 4 days straight (no
overheating). And has started to become noticeably brown. Needless to say I'm
thankful for it.

------
okasaki
Where do you get these parts in the UK?

The MERV 13 20" filter is 140GBP on amazon.co.uk and 20" box fans are
40-50GBP.

------
smmnyc
Is there an advantage to attaching the filter to the front of the fan so air
is blown through it (as shown in the video) versus taping it to the back of
the fan so air is sucked through it? Just curious if that would make any
difference. It might be easier to get the filter to stay if it's getting
sucked to the fan.

~~~
io_io
I would guess that it works similar to a water pump- pushing is always more
powerful than sucking - but check this out for some detailed analysis (and
more data on DIY air filters) [https://smartairfilters.com/en/blog/where-
should-an-air-filt...](https://smartairfilters.com/en/blog/where-should-an-
air-filter-be-placed-relative-to-the-fan-for-best-efficiency/)

~~~
patrioticaction
I never would've guessed turbulent air would be more difficult to push but it
makes total sense! Great find.

------
51lver
I used a very thick (4") filter rated for smoke particles when the wildfires
this year blew their smoke down to Seattle. The filter went from white to a
very interesting shade of grey in 3 days. Wife was able to sleep again though,
so it does work very well in my experience. (20x20 fan, filter on intake side)

~~~
Kadin
Out of curiosity, where were you able to find the big 4" thick filters in the
20x20 size? I wasn't able to find anything other than the usual 0.75 thick
furnace dust filters in 20x20 for a box fan.

~~~
lubujackson
I just bought a 4 pack from Amazon Prime Now in SF, YMMV.

------
cheunste
I been pondering about this solution for months since my air purifier died
back early summer. I also have an additional idea to make it more automatic by
using a raspberry pi, hooking it up to a powerswitch tail (essentially cutting
power to a fan) and have it automatically turn on and off depending on time of
day, etc.

~~~
io_io
I have mine on a homekit enabled outlet ($20) for scheduling and presence-
based triggers. Unfortunately I haven't found a homekit enabled air quality
sensor to pair with it.

~~~
pat2man
Eve room? [https://www.evehome.com/en/eve-
room](https://www.evehome.com/en/eve-room)

~~~
io_io
Thanks! Last I checked they were no longer selling version 1 of this product
and hadn't released version 2 yet. This might fit the bill.

------
davio
Repurpose this device as a jerky dehydrator too: [https://altonbrown.com/beef-
jerky-recipe/jerky-blowhard-3000...](https://altonbrown.com/beef-jerky-
recipe/jerky-blowhard-3000/)

------
mynameishere
They used to sell these--box fans with connections for furnace filters. I
found it strange that they never caught on, and now you can't find them
anywhere.

------
peepopeep
I was looking up air quality monitors but can't seem to find any on amazon
with a calibration certificate that will accurately measure 0.3 micro
particles. Am I the only one who thinks this is a great opportunity for a
smart product with an app that has the features of a professional air quality
monitor and simple UI / UX? If such product exists, does anyone know where I
can find it?

~~~
io_io
With the recent California fires, I've been looking for a decent option.
Unfortunately the Elgato Eve sensor is no longer sold, and the few other
consumer products still hover in the $100+ range with poor reviews.

PurpleAir sells an indoor sensor, but it appears to be limited release and
somewhat 3D printed. [https://www.purpleair.com/](https://www.purpleair.com/)

~~~
pat2man
The new version of the Eve Room sensor seems to be out:
[https://www.amazon.com/Elgato-10EAM9901-Generation-
Technolog...](https://www.amazon.com/Elgato-10EAM9901-Generation-Technology-
Temperature/dp/B07GKVBYKV)

~~~
lprd
How does Eve Room compare to the Netatmo Home Coach?

------
pwarner
I've been running a 3M Filtrete MPR 2800 in my furnace filter.
[https://www.purpleair.com/](https://www.purpleair.com/) confirms it works.
There house averages maybe 60 PM 2.5 vs 200 outside. Don't know how good it is
for furnace, but it hardly runs otherwise in Northern CA.

~~~
mikenew
Do you have two air sensors, or do you just have one indoors and compare it
with weather data?

~~~
pwarner
I am relying on 2 purple air sensors 10 miles away in opposite directions for
an outside estimate. They are usually within 10%, and we are in the same
valley, so should be close. I also see when I stop the furnace fan, levels
spike. Then drops when I turn on again...

------
thewhitetulip
Edit: plants do nothing to particle matter in air they can soak up co2,
benzene, formaldehyde etc but do ample resesrch before placing plants in your
bedroom. Typically snake plants are fine in bedroom as they don't give out CO2
at night.

There is no need for an air purifier if you have ample light in your room.
Just plant a few indoor plants

Peace lily

Rubber plant

Snake plant

Spider plant

Aloe vera

Money plant

Orchid

NASA has done a study in the 80s and these plants have purified a lot of
harmful gases including Benzene, formaldehyde, CO etc

Please use more plants!! And on top of that few plants like Snake, Aloe give
oxygen during day and night so they are refreshing (as in they don't just
clean air they give oxygen as well) and plants are cheaper and require just
water and fertilizer every once in a while.

I own 40+ plants in my balcony garden itself. I've experienced these effects
first hand!

~~~
TeMPOraL
Apparently this NASA study needs a huge asterisk next to it.

[https://news.ycombinator.com/item?id=18193622](https://news.ycombinator.com/item?id=18193622)

~~~
thewhitetulip
What? I have read the report myself. They put in Benzene inside a sealed room
and one of these plants. A few hours later the Benzene was gone! Absorbed by
the plant.

They did the same with formaldehyde too and other harmful substances.

Isn't that the bar for purification? This is still better than mere air dolter
that are costly and requore frequent maintenance

~~~
TeMPOraL
I think the key term here is _sealed room_.

And this does not invalidate the study, only helps evaluate the results in
context of applying at home or office. I.e. it's still gonna help, but unless
you restrict your airflow, not as much as you'd like.

Though the same caveat probably applies to all air purifiers too.

~~~
thewhitetulip
>Though the same caveat probably applies to all air purifiers too.

So whatever reservations you have against plants as air purifiers apply
verbatim to commercial air purifiers. Then why the bias against plants?

Funny how you contradicted yourself, not to mention those downvoting me for
speaking about plants and yet being enthusiastic about air filters!!

~~~
TeMPOraL
I didn't downvote you and I didn't contradict myself, I only posted a link
that urges precise understanding of what the study does and does not show, and
to what extent. I have no bias against plants or in favor of commercial air
purifiers.

~~~
thewhitetulip
You did not downvote me. But you did contradict yourself.

On one hand you say the focus on NASA study is on the word "sealed". That
would directly mean that you believe that plants as indoor purification would
not be helpful if there was no sealed environment

And then you say that "the same thing would apply to air purifiers"

You clearly have a bias against plants, as do the few who downvoted me. I know
you didn't downvote because HN doesn't allow you to do that!

The study which you have linked says that "more research needs to be done to
check air purification" and guess what? They are going to do a study in a
sealed environment because if a plant can remove Benzene, Formaldehyde and
Toulene in a sealed environment then it can do the same when its not in a
sealed environment. You cant5 shrug the results of NASA study saying "it was
done in a n atypical environment", of course it was done in a sealed room.

The NASA study would have been refuted if no amount of Benzene was removed by
plants. That'd mean that it is a waste of time and space for air purification,
but they are not. Peace lily and Orchids removed Benzene. Period. Whether it
was a sealed environment or not doesn't matter because results matter.

When a plant that costs less than 100$ has proven to remove harmful gases in a
sealed room, I can't wrap my head around the logic of "debunking", the myth
and going for a commercial air purifier that is costly af.

And why I say you contradicted yourself is that you criticized plants for
being in a sealed room for being effective and then at the end you said "the
same things apply to a regular sir purifer too"

This is exactly the fallacy Mr Trump had spoken to in a rally. He had said
"I'll build a 100foot wall", the Mexicans will climb the wall, sure but they
won't jump, unless of course they use ropes"

Yeah, they will use ropes and they will cross if they want to cross. That's
not contradicting, it's a stupid logic.

Same issue with your case against house plants. "Keyword is sealed"

Which study has proven that air purifiers available in the market have done
well in an aerated environment? The recommended way to use a commercial air
purifier is to close doors and windows. __Same __issue as plants so if you
recommend commercial purifiers over plants despite them both facing same
shortcomings then you are biased against plants. End of story.

------
yborg
So I did this with a cheap $15 box fan and a MERV 13 filter. It performs very
poorly, the filter impedes the airflow too much and the fan actually will
intake most of the airflow from the front corners of the output side because
it's less resistance. Axial flow fans only operate efficiently at low static
pressures. This is why your home forced air system uses a centrifugal blower,
which is more efficient at high static pressures.

tl;dr I'd use a MERV 11 or less on a cheap box fan. You aren't going to make a
Class 100 clean room out of your house with this kind of setup.

~~~
woogiewonka
Your comment should be at the top of this thread. This guy never mentions fan
performance after applying a strong filter like Merv 13. I did the same and
the airflow is reduced significantly. Since other systems use a strong motor,
this box fan contraption does not compare in the slightest. You'd have to have
it run at high setting ALL the time. Imagine that...

------
giardini
Similar items are commercially available:

"The Fan Buddy is an electrostatic washable fan filter that attracts and
captures airborne dust, pollen, dust-mite debris, lint, mold spores and pet
dander. It will also help reduce smoke and smog. This Fan Buddy fits on most
20 in. box fans... "

[https://www.homedepot.com/p/Fan-
Buddy-20-in-x-20-in-x-1-in-W...](https://www.homedepot.com/p/Fan-
Buddy-20-in-x-20-in-x-1-in-Washable-Fan-Air-Filter-FB-
BF-20/206210062#product_description)

------
ggregoire
Might be a stupid question but does this work for external air pollution? I
live at the 20th floor in a city with terrible air quality and we open the
windows once or twice a day.

~~~
mannykannot
I imagine it would help with particulate matter (such as smoke, whether
visible or not), but I do not think it would have any effect on gases such as
ozone, sulfur dioxide or nitrous oxide.

~~~
ed_balls
That's correct. HEPA filters anything bigger than 2,5 μm e.g.
[https://en.wikipedia.org/wiki/Benzopyrene](https://en.wikipedia.org/wiki/Benzopyrene)
and NO2, SO2 etc. are 1000x smaller.

------
lilbobbytables
I've been using a setup like this for the past year. I use a 4" think filter
to reduce strain on the motor though (it's pleated, so a lot more surface area
to pull air through than the thinner ones), the idea being reduced strain on
the motor. I also stick a carbon pre-filter in front of it.

I get smoke wafting in from outside via window air conditioner - and I think
my neighbor occasionally smokes in his room.

I'm planning to setup another to better cover my open floorplan.

------
rustychris
In case you're curious how this does with wildfire smoke -- Oakland 1 bedroom,
put a 14"x20" MERV 13 (filtrete blue) filter on a box fan (covering the extra
6" with paper). Had a PMS5003 from adafruit monitoring before and after. In
the span of 3 hours indoor PM2.5 dropped from 25 to 5 ug/m3 and has stayed low
since.

[https://imgur.com/IxdxhV2](https://imgur.com/IxdxhV2)

------
dmourati
I have the ~$800 pro version early in the video. It's an IQAir. I bought it
when I bought my house. We were refinishing the hardwood floors and have a
small child. My goal was to knock down the VOCs to make the room safe for him
prior to move in.

It runs 24/7 in my bedroom now. Huge improvement in sleep quality. I've only
had to change one of the filters once for about $100 after 1.5 years of run
time.

------
gregwebs
I have been quite happy with the top pick from this review:
[https://thewirecutter.com/reviews/best-air-
purifier/](https://thewirecutter.com/reviews/best-air-purifier/)

Although the price of that purifier is now $40 more then when I bought it, so
it may make more sense to look at their other picks.

~~~
ar_turnbull
I have the same one and think it’s great. Bought it when the wildfires in
British Columbia blew over and turned Calgary into an apocalyptic wasteland.

Air quality was bad and I’m still not sure what kind of filtering my condo
building has.

------
rubatuga
Tried this exact same thing. Unless you are a "fan" of noise, and the
inability to sleep next to it, go ahead. It's not worth it IMHO. I ended up
just turning it on whenever I left the house, but even then my roommate
started getting annoyed from the other side of the apartment.

------
Dowwie
To what extent will a box fan like that successfully circulate most of the air
in a room through the filter?

------
Havoc
Given how cheap the commercial ones are I'm not sure I see a point. Esp given
the fact that the motors in box fans are unsuitable for the task.

I just ordered a wifi plug for mine though so that I can set it on a timer /
hacked amazon dash button. It's not but the slight whoosh is annoying

------
walrus01
Over the past two years as BC and WA have had terrible forest fires, this
exact solution has become quite popular for people who are willing to DIY. the
air quality in mid summer 2018 in Vancouver was really quite bad, exceeding
Delhi or Beijing pm2.5 figures for weeks.

~~~
selimthegrim
Was Seattle as bad PM2.5 wise?

~~~
walrus01
Yes...

[https://www.vox.com/energy-and-
environment/2018/8/21/1776190...](https://www.vox.com/energy-and-
environment/2018/8/21/17761908/seattle-air-quality-haze-smoke-wildfire-health)

------
vic_b
I have found this on amazon seems like someone is already build a complete
prototype. [https://www.amazon.in/Smart-Air-DIY-Purifier-
White/dp/B01CP5...](https://www.amazon.in/Smart-Air-DIY-Purifier-
White/dp/B01CP55QXS/ref=pd_sbs_79_2?_encoding=UTF8&pd_rd_i=B01CP55QXS&pd_rd_r=979f7ddc-e969-11e8-8bb0-a509d9a0f381&pd_rd_w=fULSI&pd_rd_wg=QMAYi&pf_rd_i=desktop-
dp-
sims&pf_rd_m=A1VBAL9TL5WCBF&pf_rd_p=9fc668a0-2aac-4fb6-970f-606919bc0185&pf_rd_r=QA1DHXPWYMCWEE2HCYPG&pf_rd_s=desktop-
dp-sims&pf_rd_t=40701&psc=1&refRID=QA1DHXPWYMCWEE2HCYPG)

------
ksec
Do we have any other alternative to HEPA filtering, or something that last 5
years without me paying to replace it every 1 - 2 years? All the current Air
Filtering system are like Printers, they earn more money with the yearly
filter replacement.

I also wonder if it makes sense to have an Air Filter if I have my windows
opened 80% of times? I like the better Air Circulation, but the Air Quality
aren't exactly great either.

We now live in a world with pipes that have potential toxic materials and
water contaminated so we need Water filtering system, and Air pollution that
needs Air filtering system.

~~~
Elien237
Particle filters such as HEPA are unfortunately by nature only effective for
roughly 6 months, then they are clogged. You can vacuum them to get rid of the
biggest particles and then use them for another 6 months (total 1 year), but
then they are clogged at molecule level and are perhaps only 25% effective of
its original efficiency and won't do you any good. The washable ones are not
good and the ionization air purifiers without filtration are a scam. Particle
filters are the best way to give you good air quality. And unfortunately you
get what you pay for. When it comes to carbon filters they don't work for more
than 6 months - no matter how good air quality you have. Carbon will absorb
till it finds equilibrium then start to release smells and some gases. Shelf
life of an opened package is about 6 months even if you don't push air
through. Depending on the air quality in your local area (Bombay smog/wild
fires/countryside clear skies), your filters will be clogged eventually and a
rough estimation is 4-6 months in high polluted areas, and 1 year in less
polluted areas). Turn the air purifier off when you have the windows open. It
makes no sense to use it if you let pollutants in from outside, even if your
indoor quality is bad.

------
js2
Also works for dehydrating fruit:

[http://frugalvagabond.com/the-box-fan-dehydrator-
experiment/](http://frugalvagabond.com/the-box-fan-dehydrator-experiment/)

------
jakeogh
These work excellent. I put a finer filter on the output. Clear difference in
the pollen seasons, but I just let it run all year and swap the (visually
clogged) input filter every few months. The FPR10 output filter lasts longer,
but you gotta take a look at the side facing the fan to inspect it.

Also, consider adding output filters on any AC units (ducting etc). Even a
"new" AC system can quickly become a source of particulates, or (way) worse.

------
Qerub
Nice synchronicity that this was posted the same evening I got a ~160 USD
Xiaomi Air Purifier 2
([https://www.mi.com/global/air2/](https://www.mi.com/global/air2/)) delivered
home. Might be a good alternative for those who want an off-the-shelf product,
a pretty design and "smartness" like scheduling.

~~~
woogiewonka
Scrolljacking on this site is unbelievable.

~~~
vinay427
I didn't notice any? I just tried with my ad/tracking blocking disabled as
well.

------
LinuxBender
I think this is a cool project idea, but I would not use this as a primary
means to filter air unless you can't afford a proper hepa filter unit and you
happen to have parts laying around to cobble this together. Smoke and mold are
dangerous to breath and you only get one life. This is probably a good way to
augment your existing filters, in my opinion.

------
Cthulhu_
Wouldn't turning on the extractor in your kitchen have the same effect? If
you've got the correct filter in there anyway.

~~~
strstr
If the filter type is right (as you mention) yeah that would make sense.

If it vents outside though, not necessarily. Running the extractor would drop
air pressure and pull from elsewhere (particularly bad during times with low
air quality).

------
ipsum2
Has anyone tried constructing a UV-C based filter before? You would need to be
careful to make sure no light leaks out.

------
soneca
When and for how long should I leave this turned on to be effective in
removing dust particles in my small bedroom?

~~~
adventured
Are you ok with white noise while you're sleeping and air flowing in the room?
If you're ok with those things, run it while you're at home and sleeping. If
you go to work during the day turn it off then, and turn it back on when you
get home. It should rapidly clean up the air in a small bedroom.

The only real issue is any continual air flow into the room. There will be a
big impact from what kind of air system you have in the greater building. For
example, central air without a good filter on that system will make your fan-
filter's job a lot harder.

The filters are relatively cheap to replace and will last a long time
filtering a small bedroom. I get a solid year out of the filter on my central
air system and it's filtering an entire home (non-smoking, no pets). Outside
of the small electrical cost or annoyance from having the fan running, there's
no reason not to run it very frequently if you derive a benefit. If you don't
desperately need purified air for eg allergy purposes and your small bedroom
isn't receiving inbound air (eg from a central air system), run it for 20-30
minutes, a few times per day, and that should easily do the job. If that's a
hassle, just let it run more often than not.

------
MarkMc
I worry about air pollution especially when I'm in Jakarta or Singapore so I
bought the Dylos DC1700 air quality monitor. It is great to know exactly how
bad the pollution is and how effective my air purifier is - I feel like I'm
walking around with x-ray vision.

~~~
adakbar
Know any merchant who sells Dylos DC1700? I'm in Jakarta too, kinda hard to
find these kind of hardware

~~~
MarkMc
Sorry I don't know anyone who sells in Jakarta. I purchased it on Amazon.com
and used the myus.com service to forward it to me. It's expensive but worth it
for my health.

------
nathan_f77
That's a really good idea. I was planning to buy one for a few hundred
dollars, but I should just do this instead. The burning season is really bad
in Chiang Mai (lots of smoke in the air for about 2-3 months), so it's good to
stay indoors and have an air filter.

~~~
kilroy123
Off topic, but hey so I just moved to Chiang Mai. Do you think it's worth even
sticking around here during that time? I was thinking about just heading to
Bali instead. Not sure how bad it really gets.

~~~
nathan_f77
It's really awful, especially if you're sensitive. Some people aren't bothered
by it too much, but it really affects me, so I try to get away. We have some
pets, but it hasn't been too hard to find a house-sitter. (Although I always
feel a bit guilty, and try to be honest about the smoke.)

These articles are concerning:

* [https://www.theguardian.com/environment/2018/aug/27/air-poll...](https://www.theguardian.com/environment/2018/aug/27/air-pollution-causes-huge-reduction-in-intelligence-study-reveals)

* [https://www.scientificamerican.com/article/air-pollution-a-l...](https://www.scientificamerican.com/article/air-pollution-a-leading-cause-of-ca/)

I think we'll move to a new city or country in the next 12 months. I don't
think it's wise to go through burning seasons once a year for a few decades.
(It's actually the only reason we want to move, otherwise Chiang Mai is an
amazing place to live.)

Bali would be a good option, or even the south of Thailand if you have some
more time on your visa. Koh Lanta is great.

~~~
kilroy123
Awesome thank you much for the links! It seems like a very awesome place so
far. I'm loving it.

------
baby
I've been luring the Dyson hot and cool air purifiers, it's pretty silent from
what I've heard, it also serves as both an electrical heater during the winter
and a cooler during the summer. The price tag is the reason I've never bought
one...

~~~
glibgil
> cooler during the summer

Where does the heat go?

~~~
tjohns
It's just a fan + heater. It's not an air conditioner, nor is it marketed as
such.

I have one. It works pretty well. The air filter isn't as good as the massive
Austin Air I use for my living room, but it's okay for a smaller room... not
to mention much quieter, smaller, and easier to integrate with home
automation.

------
Fej
How fast does this burn out the motor? Legitimate question. I _just_ built one
of these.

------
Elien237
I’ve been reading and following these comments now and I’m both impressed and
horrified at the same time. As a mechanical engineer, product developer and
developing air purifiers specifically for 5,5 years in combination of filter
expert till just 6 months ago. I now work in another industry. You can ask me
anything and I’ll do my best and be as unbiassed to brands as possible if you
want me to.

There are a few things you need to know for your own safety if you do DIY and
want to reduce costs: Fan and filter are the heart of the unit. This is where
you put the money even if you want to do a temporary solution. The housing can
be cheap, but please be smart and never leave a DIY unit alone since
electricity is involved, they are not safe. Once you’ve bought all this
equipment, you’ll soon realize you have put out a cost of a reasonably good
air purifier.

\- You need to have a good amount of space between the filter and the fan to
cut pressure drop – otherwise you will overload the fan, you get a high
electrical bill and it becomes a fire hazard or it will break down = your
money is not well spent. This is why you see some units on the market looking
hollow – the space is there for a reason. \- Fans. Look for a strong motor
that can handle air resistance. Regular fans are not made for resistance and
will break, stop (programmed) or even start a fire. Also look at the airflow
rate and the safety regulations of it. The higher airflow rates the better.
When it comes to fans, you get what you pay for. \- If you use a weak fan and
a thick filter you will only clean the air closest to the fan, not the actual
room air = money not well spent unless you use the purifier right in front of
your mouth/nose. \- HEPA filters are actually not that great... There are
newer filter types on the market that are less dense but still not as
effective. HEPA can be too thick/dense for the fan to be able to pull air
through, or the air doesn’t have high flow enough to clean more than just the
air next to the purifier. You need to have circulation. Especially fans that
are made to only move air without resistance, the motors are not adapted for
this. If you have a strong fan you can use HEPA (Merv) since it can power
through. Also, if the filters are too thick, air leakage will occur, motor
will sound horrible, and the air will pass on the side instead of through the
filter = noises, whistle sounds and less clean air. Yes, duct tape is good
here if you build it yourself. \- Put the filters in front of the fan (before
fan) to spare the life of the fan – the dirt will not accumulate and destroy
the fan over time. To get (collect) dirt in the filters is the goal. Some fans
can handle dirt passing through and then you can have the filter after.
However, if you just buy a regular air fan in a regular store, I don’t suggest
having the filter after the fan (air flow direction). \- If the filter gets
super dirty quickly, you can vacuum or gently whip it outdoors to recover some
lifetime. However, after some time (roughly 1 year in normal use) it will be
clogged no matter what you do. There are no filters or technologies better
than particle and carbon filters available today. The 6-months to a year
lifespan is actually accurate in normal conditions. I’ve been doing these
tests in China, India and Europe and US several times in different conditions
(both lab standard and normal homes) and with different units/tech/brands etc
and can confirm particle filters + ionization is the best tech available and
the filters last 4 months-a year depending on local conditions. The filters
are usually functional after a year as well, but with very low efficiency. \-
Pre-filters are great since they take on large particles like pollen or ashes
before it hits the main filter. Just make sure it’s not too dense. \- Fully
made air purifiers are tested by 3d party institutions unbiased to payments or
commercial, certified and heavy controlled before released on the market. You
can check consumer reports, AHAM and California Air resource board (ARB) or
Chinese GB-standard websites for different type of tests and results if you
want to know which ones are really, really good. Some complain that they are
in “lab environments” but it’s still really good products that does the job
even in real life conditions. \- If the unit you want is not in their lists of
tested products, it’s a warning sign that the product is not good, or might
not even qualify as an air purifier… It’s a surprising large number of big
brands that make terrible products but are good in marketing or simply rely on
their names. \- Fully made air purifiers have fans developed specifically to
match the filters resistance and won’t break down after a few months or start
a fire if put under heavy resistance (clogged filters). The filters last
longer since its optimized for air treatment in home environments. Usually
other technologies are a part as well such as ionization or UV or similar.
That’s why they are more expensive. They are super important in a development
of air purifies. Some of them also have IP44 certified fans meaning they can
work during humid conditions without breaking or causing short-circuit/burn
outs or worse. \- These DIY things work, but are usually not cheaper in the
long run and are not as effective as the real purifiers. If you suffer from
fires, smog, allergies etc I highly suggest getting a real purifier incl
filtration+ionization since those things are very harmful, especially for
children. If you just like to temporary fix something these DIY will work if
you do it right.

I hope I could answer some of your questions.

~~~
stamps
Thoughts on Photocatalytic Oxidation?

I have a Vornado's unit and the call it "Silverscreen."

------
NoblePublius
I’ve been doing this for years. Cheaper drugstore fans can’t handle the drag
of the filter and will burn out. Kind of amazing that no one makes a box fan
with slots for such a filter.

------
ocdtrekkie
Insanely simple idea when you think about it. Side perk: My furnace uses the
same size filters, so it won't even be a hassle to stock ones that fit a box
fan.

------
yonran
Is there anywhere you can get a good blower fan for the purpose of filtering
the air, instead of a box fan that has a lot of space around the blades?

~~~
vt240
Grainger [1] search for "industrial Blowers and Accessories" would probably be
a good place to start looking. They tend to be expensive though. Take a look
at McMaster-Carr [2] too.

[1]: [https://www.grainger.com](https://www.grainger.com)

[2]: [https://www.mcmaster.com/](https://www.mcmaster.com/)

------
squarefoot
Can those filter be washed? People living near car congested areas would
benefit from them the most but should also swap them more often.

~~~
woogiewonka
I don't think so. The filter he uses has to be replaced every 3 months and it
costs ~$15 (that particular brand). So you are looking at $60/year in filter
costs - all in all not bad! Also, you could stick a carbon pre-filter right in
front of the fan (behind this filter) of it to filter out some of the odor-
causing particles.

------
noobermin
You've got to be kidding me. But yes, if you literally have a fan and a filter
then why do you need to spend more money.

------
Odenwaelder
Cool! You could use a smart plug and a fine dust (PM10 and PM2.5) sensor to
start the fan only if the air is bad.

------
xhruso00
That guy's wearing a doctor coat and has lots of books on the shelf so he is
legit for sure.﻿ THUMBS UP.

------
adakbar
Is there a place where I can get information about the MERV rating of certain
HEPA filter products?

~~~
xVedun
MERV info:
[http://www.mechreps.com/PDF/Merv_Rating_Chart.pdf](http://www.mechreps.com/PDF/Merv_Rating_Chart.pdf)

------
patrickbuckley
Does anyone know if this type of setup would be good for smokey air from
California wildfires?

~~~
rustychris
It works - we measured 25 down to 5 ug/m3 drop over 2 hours in an oakland
townhouse. Measured with hobby grade (pms5003 from adafruit) hardware, so
absolute numbers probably not that accurate, but the effect was clear.

------
lmilcin
I see some comments on fighting mold and smells, I have an experience devising
my own protocol that was extremely successfull in my case.

Few years back I was desperate to find a large apartment in an area where they
are just not available. I found one, extremely cheap, that the owner could not
find anybody to rent to. The apartment was all but destroyed by previous
occupants -- there was substantial mold in most rooms, heavy cigarette smell
that was completely masked by even worse problem -- monkey pee and feces on
every flat surface in the apartment.

Being geek I decided I will try what I can do and in the end I devised a
protocol to treat the apartment. My girlfriend was very sceptical. A month
later I brought her to apartment to the smell of fresh furniture and she was
instantly converted. There was no fresh furniture, it was just the other
smells were completely eradicated.

The only smell I could not get easily off and lingered for many months was
banisters that were painted over with lacquer by the owner before I had the
chance to treat them.

The treatment was:

1\. industrial ozone generator (200 USD) + 200W fan + air dehumidifier (ozone
decays quickly in humid air) + programmable timer and remotely controlled
(over Internet) AC socket to control fan and generator (this let me turn the
fan for 20 minutes every hour and let me turn everything off 3 hours in
advance so I can visit safely without being subjected to high levels of
ozone). This setup was on for an entire month except for when I was visiting
to do other stuff in the flat.

2\. 35% hydrogen peroxide mixed with baking soda. Ozone kills mold, binds and
oxidises any smells except for urea crystals. To neutralize urea crystals you
first have to dissolve them and treat while in dissolved state, before they
crystalize again. I don't know what baking soda does, exactly (except for
making cleanup tougher...) but I found dissolving some improves the treatment
with hydrogen peroxide. I sprayed every surface (walls, floors, furniture,
etc.) in the flat with this mixture enough to get it wet so that it dissolves
and reacts with urea crystals.

Now, mandatory WARNING: both concentrated ozone and 35% hydrogen peroxide IS
EXTREMELY DANGEROUS, you absolutely MUST spend time researching how to handle
this stuff safely.

The hydrogen peroxide at that concentration INSTANTLY BURNS ANY ORGANIC MATTER
IT IN CONTACT WITH. This includes your lungs and eyes if they come in contact
with vapors or mist.

Concentrated ozone may also leave lasting effects on your eyes and lungs.

MAKE ABSOLUTELY SURE NOBODY ENTERS YOUR FLAT WHILE IT IS BEING TREATED, MAKE
SURE OZONE IS NOT VENTING TO OTHER APARTMENTS, ETC.

One minuscule drop of 35% hydrogen peroxyde touched my finger and it felt as
if I was shocked with electricity and the skin was instantly burned white.
Don't even think about getting close to it without heavy nitrile gloves and
face mask.

The fumes and mist will be extremely dangerous, I have used full face mask
with external breathing aparatus to be on the safe side while I was spraying
entire flat with it.

Test the effect on any surface before treatment and dilute with water until it
becomes safe for that surface. I have destroyed some stuff at the kitchen
where it reacted with plastic foil on otherwise metal oven exterior, etc. I
ended up diluting it for everything except stained walls. For furniture I
diluted it to around 5-6% hydrogen peroxide, for floor panels to around 9%.

ALSO, very important, 35% hydrogen peroxide naturally decomposes producing
lots of hydrogen so if you store the containers for longer than few days you
have to constantly monitor them and vent hydrogen before containers burst.
Once you finish your treatment, get rid of it as quickly as possible -- it is
a liability while you are storing it.

On the upside, and this was very important to me, this does not leave any
lasting dangerous chemicals in your flat. Both the ozone and hydrogen peroxide
decompose naturally into harmless products and baking soda is the only think
you can really work to get rid of but only for cosmetic reasons -- so that
your entire flat does not look as if it is covered in dust.

~~~
mnw21cam
Hydrogen peroxide decomposes to water and oxygen, not hydrogen.

~~~
lmilcin
Ah, you are of course correct. Still, it will burst your bottle the same way
hydrogen would.

------
oblib
I use this same setup and it works great. Been doing it for years.

------
tra3
I wonder if you can put a filter on both sides of the box fan.

~~~
TylerE
There would be very very little gain from doing so, but you'd probably kill
the motor.

HEPA filters are very very very good. Running through 2 of them isn't going to
pull much more out because there just isn't much more.

Actually, you'd probably get less actual filtration due to the greatly reduced
airflow.

~~~
tra3
Why would it kill the motor? Load is reduced when airflow is restricted.

If the first filter reduces 90% of pollutants, can we assume that the second
filter reduces an additional 90%?

------
agumonkey
Anyone knows how to DIY microfilters ? or even nanofilters ?

------
fenwick67
At first glance this looks ridiculous until you realize it's a doctor from U
of M's health center demonstrating its effectiveness

------
Andymoore
mine brother too working in construction business and having same breathing
problem.

------
chanandler_bong
reddit.com/r/thereifixedit

------
grendelt
> "Videotaped"

haha. Seriously? It was on tape?!

------
user764743
You could also buy a plant.

~~~
oh_sigh
Plants don't remove particulate matter like an air purifier does

------
chefsaroar
Hi

------
black-tea
Would this do anything to help with air pollution from a nearby road? I'm
thinking particulates from diesel fumes.

------
CathyWest
What kind of furnace needs this high level of air purity to operate? I would
have thought a grating that prevents rats and squirrels from wandering in
would suffice. I would assume small particulates would just burn with the rest
of the fuel with no ill effects.

------
jordache
literally HACKER news

