Permeable Materials in Homes Act as Sponges for Harmful Chemicals: Study

Also, don’t put a HEPA filler in your HVAC return — not only is it unhelpful overkill, it will have excessive static pressure drop, thus wasting power, increasing noise, reducing airflow, and potentially damaging the blower. Use an appropriate filter in the MERV 13-16 range.

Hackers may prefer other options.

The cheapest real ones I've found are on the order of ~$150

So many seem to rely on automatic ‘calibration’ - which just seems to consist of “let’s assume the lowest sensor readings of the last while correlate to baseline atmospheric CO2”.

For a meter that’s never taken outside, this is obviously going to mean it’s reading too low all the time after a few ‘calibration’ cycles. And, worse, it's likely to be more wrong in less well ventilated spaces.

You calibrate it by setting it outside for a bit to establish the baseline and then bring it inside. The detected CO2 level noticeably tracks with the number of people in the living room in which it is located and whether outside air is being pulled in, either due to the furnace or having multiple windows open.

We do not use the app, so I can't comment on that. And my only complaint is that it has to be plugged in otherwise it runs out of power in an hour or two.

My problem with this advice is not that it's difficult to measure pollution levels (it really isn't), but that there's no "fresh air" outside for many of us. In many parts of the world, the air is significantly worse outside than inside even without running an air purifier (and with a purifier the difference in particulate levels can run into 100× or more during winter).

Some years ago I looked at the few papers that measured the difference in gaseous pollutants (like NO2 and SO2) inside and outside with windows open and windows closed, and for some reason closed windows do provide limited protection against them. Nobody really understands why AFAIK, it shouldn't work that way since they're mixed with air in a gaseous mixture from which they can't be filtered out without a specialized chemical filter, but it does help.

https://natural-resources.canada.ca/stories/spotlight-energy...

Das ist nicht genug und klingt ehrlich gesagt grauslich.

Not German approved.

https://ambientweather.com/indoor-wireless-air-quality-monit...

We have low-voc foam in the attic, which outgasses voc’s slowly and constantly. (They measure voc release at application time, not over the product lifetime).

I started actively venting the attic a two months ago. The whole house reeked of foam for a week or so whenever the windows were closed.

It’s fallen off a lot, even though the attic foam is 5 years old.

I think the sponge analogy is correct. If the house is sealed, the VOCs accumulate in the atmosphere, and are reabsorbed into the foam at the rate they are released into the air.

If you leave the house completely open, the outgassing will not be offset by reabsorption.

I think the CO2 in our place accumulates faster than the VOCs I can smell, so opening the windows when the meter tells us to keeps the net rate of outgassing high, and the indoor pollution low. It seems like the outgassing is slowing down now.

I really should get some VOC meters.

Sounds very country dependent. I really doubt it's true here in the UK. But then, UK housing is just garbage all around unless you build something custom and put a lot of money and attention into it.

It's easily the favourite thing in my home. It filters the outdoor air, reducing pollen and mosquitoes. It keeps out excess moisture in summer. I don't have to open a window when it's cold. It automatically goes into overdrive after a particularly steamy shower. It's great.

Yes you have to take into account running an air filter for PM2.5, closing the window while a truck is idling outside, running your humidifier or dehumidifier if you want.

But you need fresh air coming in somehow, at a certain rate. There's no way around it. Pollution in terms of VOC's, and CO2, is always higher indoors than outdoors, because things indoor generate it and don't remove it.

I’d like to do a custom build like you so the fan speeds are variable.

I have a purple air sensor outside. One day I'll get around to making the air exchanger smart enough to turn off when the smoke from fires makes the air outside worse than inside, it turn off the air exchanger when inside air is good enough, etc.