My dad had a balanced heat recovery ventilation installed few years ago. I think it might be undersized a bit as it’s somewhat loud when running at 100%. He doesn’t like the noise so he runs it at 40% or so.

After getting meter I found it’s def not enough, especially in rooms with more people doing some activity. He still doesn’t believe my meter is accurate tho.

I thought our ventalation was fine. Then we got at CO2 sensor for covid related reasons. When we replaced our 30 year old windows the numbers went through the roof.

We updated our air exchanger to fix the problem. Venmar and Vanee are two big brands in america.

I live in Germany, and here the houses generally don't have machine ventilation so one has to air manually and regularly. As an example: earlier today I closed the door to my office (ca. 18 m2 / 194 sqft). The window was closed. After 2 hours the CO2 levels rose from 935 ppm to 1966 ppm. Letting air in for 20 minutes reduced the CO2 levels to 869 ppm.