HRVs also let you control where the fresh air comes in and where the stale air leaves. This means you can do clever things like bringing fresh air into bedrooms and removing air from bathrooms.

Thanks. I really hope hrv systems become standard. My brother has one in his house and it seems to help keep down co2.

Do heat pumps ventilate? I have one in my new apartment and co2 seemed higher when it was off. But I was told they are not hrv systems. Maybe the blowing fan just caused more air circulation.

Home heat pumps generally do not have an outside air connection. They assume that your house is drafty enough already.

At least here in BC, I believe it is code to include a fresh air vent with any central HVAC. Our house has one (built in 1992). Of course, if the house is tightly sealed and you don't have an exhaust fan running, it won't suck in much outside air.

Since the climate is moderate where we live, what's been suggested to me is to just run the recirculate fan often/always, and to use bathroom exhaust fans to control fresh air turnover. (As built our bathroom fans are hooked up to a central humidity sensor, and will turn on when house humidity reaches a set level (as well as being able to turn them on in the bathrooms). I'm actually curious whether something exists, or I could rig something up, to turn them on based on CO2 levels as well.