They do mention that CO2 levels are typically higher indoors and that Americans spend 87% of their time indoors, but it would have been interesting to see a prediction for how much sooner this would become a problem inside.

Modern houses are actually quite a problem for this. A well insulated house also tend to be quite well sealed. I’ve seen my bedroom pass 5000ppm. I suspect a lot of people are working in 1000ppm environments or higher for long periods.

For those interested, IKEA recently released a air quality sensor that does CO2 for a very low price. ALPSTUGA

One reason the window directly over my head in bed stays open all Winter.

I don’t want it too cold when sleeping, and heating a room with an open window is wasteful and expensive.

I’m personally planning on installing an air to air heat exchanger. Even a cheap one can get 75% recovery. Add in some air sensors to make it smart and it’s fairly fire and forget.