That may be. The word we use is more a property of the ventilation system ... that you blow as much air into the house as out of it, active airflow in both dire

That may be. The word we use is more a property of the ventilation system ... that you blow as much air into the house as out of it, active airflow in both directions. (As opposed to older ventilation where only exhaust has a fan.) This facilitates plugging in a heat exchanger. To be clear I did not mean HVAC, which requires (some) energy in itself. At home I do not have HVAC. However, the outbound air passes through a rotating metal structure that sucks up the heat from outbound air and releases it into the colder inbound air. Just using the temperature gradient that is there naturally. Passive energy transfer. Same principle can be used with hot water (e.g. from showers). Then one can put HVAC on top of this for active warming.