[josephst18]

I would love to find a portable air exchanger too—opening windows helps with CO2 levels but it’s inefficient for most of the year in much of the United States. Built-in air exchangers with heat recovery are available but are a non-starter for anyone in a rented place. Unfortunately, no good solution exists so far

[Natsu]

Yeah, I live in a place where, well, let's just say that opening the window for much of the year simply isn't done. I don't think some of my windows will even can be opened any longer due to having been closed for so many years.

[jeffbee]

The good solution is to simply tax landlords to get decent ventilation installed.