CO2 and ventilation experiment

February 1, 2023 8:08 AM

I borrowed a CO2 monitor and discovered that my office/bedroom is generally WAAAY too high in CO2. So I'm currently sampling some data. Can I determine anything interesting from this data.

So I vented the room entirely until the monitor hit 400 and stayed there. Then I closed the windows and doors (which is my normal working conditions) and started sampling every 5 minutes.

I'm still doing this. So far it's going up linearly. I assume it'll start to cap out at some point? Can I determine anything interesting from these calculations.
Maybe something about how much ventilation there is?
Or maybe I could figure out how many plants would be needed to counteract my CO2 output?

Not sure. Any ideas?

posted by Just this guy, y'know to Home & Garden (10 answers total)

What’s the air flow situation in your apartment? How does fresh air enter and how does the room ventilate?
posted by bluedaisy at 8:17 AM on February 1, 2023

Steady-state with all windows closed in my home office, in a 1990s-built apartment building, is around 1300 PPM according to the Aranet4 I bought on holiday sale. Opening a window in the office and a window in the adjacent living room (to get airflow going) drops me down to 500-700 PPM in less than an hour. My main conclusion was that my apartment is too tightly-sealed, and it's worth opening the windows when possible to turn over the air, rather than keeping everything shut tight. I'm lucky enough to live in a place where I can get away with opening the windows during afternoon/early evening (in the winter) or at night (in the summer) most of the time, so that's my plan going forward. Watching the CO2 meter certainly has me thinking about heat exchangers or other ways to improve fresh air circulation in homes, going forward.
posted by Alterscape at 8:31 AM on February 1, 2023 [3 favorites]

Plants aren't going to make any appreciable difference: "Do Houseplants Increase Oxygen Levels? Not really. They do add oxygen to the room, but in such small amounts that their contribution is negligible."

With regard to CO2 levels: there is some very interesting discussion in this blog post (see also the comment section). The same author also wrote a follow-up post, where he presented findings from 120-plus readers who experimented with altering CO2 levels. Spoiler alert: Reducing CO2 levels didn't seem to have a dramatic effect, though results were variable, and a small percentage of people felt much better with lower CO2.
posted by alex1965 at 8:34 AM on February 1, 2023 [3 favorites]

Mine is consistently ~600-700 ppm with two people in the house, slightly higher if we're hanging out in the same room as the Aranet4. With four people in the house, it sends it up to about 900 ppm, at which point I'll turn on an exhaust fan, which brings it back down to ~700 ppm. When my housemate had covid we had all the exhaust fans on and it was steady around 500 ppm. That's about the lower limit for windows-closed. I haven't tested it outside yet because it's super cold here.

I'm in a 1920s house that I had an "energy assessment" done on, which ultimately showed it was drafty as heck. I air-sealed everything and insulated everything, and then it was much too airtight. The energy assessment folks recommended a constant-ventilation fan that re-balances the air intake/outtake appropriately. So, all this to say that it's about as good as it can get in terms of the air ventilation and energy conservation (for an old house in a cold climate, anyway).
posted by IridescentMoth at 8:39 AM on February 1, 2023 [2 favorites]

A bit tangential to your question, but if you are worried about the quality of your indoor air, you may want to look at particulates, which are potentially more harmful than CO2. After I read this blog post, I bought two air filters: One for downstairs (I have a small house), and a smaller filter for my bedroom.
posted by alex1965 at 8:45 AM on February 1, 2023 [5 favorites]

Yes, you can get a reasonable estimate of your ventilation rate just by measuring the CO2 with you in there once it has stabilized. Here's a Twitter thread explaining. The fifth tweet gives a table that you can use to look this up.

The effect of houseplants will be minor. The number of plants you can reasonably put in your room will not be able to keep up with your breathing. You need ventilation to reduce CO2 levels, either to lower CO2 areas of the dwelling or to the outside. The ideal is heat recovery ventilation, but of course that's not practical in all cases.
posted by ssg at 9:51 AM on February 1, 2023 [1 favorite]

If your structure is relatively airtight and it's compromising the air quality, the orthodox way to address it in an energy-efficient way (that is, not simply opening windows) is to add an ERV (energy recovery ventilator), which you can think of as basically a bathroom fan that also draws in fresh air and equalizes the temperature and humidity between the exhaust and supply. Panasonic makes well-regarded models.
posted by pullayup at 11:09 AM on February 1, 2023 [3 favorites]

We have been monitoring our basement bedroom for months. With 2 of us, and the door + window closed, it could rise to over 1,100ppm CO2 at night. We would wakeup groggy, still sleepy with headaches.

With the window open a crack + window fan we never go above 700ppm - therefore the window stays open now, even when it is cold.

Highly recommend getting a monitor, ours does CO2, VOC & Radon (which is why I originally bought it - we have a basement bedroom, due to large multi-family household - thankfully Radon is always low)
posted by rozcakj at 11:18 AM on February 1, 2023

We did this and found our child's bedroom was hitting 2000+. Bleh. We installed an ERV.
posted by stray at 5:17 PM on February 1, 2023

You try an experiment where you turn on the fan for your furnace to run continuously and see how that changes the number. Our bedroom CO2 levels dropped more than 100 points with the fan running so that seemed like an interesting date point to me. Not sure what math you could do with it though...
posted by metahawk at 8:23 PM on February 1, 2023