[kadoban]

This is definitely a real problem, but it's not caused by higher outdoor CO2 levels. The levels outside are typically in the 400-500ppm range. When you're enclosed with not enough ventilation, the issue is you (and other breathing organisms) and the lack of ventilation, not the outdoor level.

The outdoor level has absolutely risen, it's just not the important factor here.

You're very lucky that you can keep windows open so often. My climate makes that impossible for much of the year; I'm looking in to getting an ERV installed asap.

[_yb2s]

I disagree- many people, especially in Europe are still using buildings designed in pre-industrial times, when CO2 levels were as low as half what they are in urban areas now. Those buildings now will have much higher CO2 levels indoors than when first built, with the same amount of air exchange. One could estimate exactly how much higher with some differential equations, but certainly in some cases it is possible to push things over the limit where there are now problems, everything else remaining the same.

Moreover, those buildings likely now have much less air exchange than when designed now that they use AC instead of open windows, forced air heat instead of unsealed fireplaces (which turn over a lot of air), and possibly have been updated to more airtight doors and windows.

[kadoban]

> One could estimate exactly how much higher with some differential equations, but certainly in some cases it is possible to push things over the limit where there are now problems, everything else remaining the same.

It's obviously in the direction of higher indoor CO2 levels, but the effect just isn't that big if you're talking about your indoor levels being 2000ppm. It's not the cause of that.

I'll see if I can math up some numbers later to quantify.

> Moreover, those buildings likely now have much less air exchange than when designed now that they use AC instead of open windows, forced air heat instead of unsealed fireplaces (which turn over a lot of air), and possibly have been updated to more airtight doors and windows.

Yes, these are the causes. Well insulated homes are legitimately great, but now we're finding out that ventilation is also quite important and wasn't well enough planned for in many cases.

It's also that CO2 wasn't easy to measure decades ago. I'm sure many homes had high levels even with no door seals and leaky windows, just nobody had a great way to know or care. I'm sure ways existed, to be clear, but it wasn't like today where you can grab a monitor on amazon on a whim.

[_yb2s]

You are correct after all. I setup some equations and solved for the interior steady state CO2 levels as a rough approximation the steady state interior CO2 levels are proportional to CO2_outside + generation rate / ventilation rate.

Therefore, steady state interior levels will only rise by approximately the same amount as the outside levels, which does seem insignificant.

[kadoban]

Thanks for doing that, I got lost in the math and couldn't figure it out in the time I had, too rusty xD