In conventional homes, air moves in and out through leaks in the building envelope and open windows and doors. That lets things inside that we don’t want to breathe in, like smoke, vehicle exhaust or pollen, and lets heat out. A high performance home is airtight, so mechanical ventilation by an energy recovery ventilator (ERV) is used to move air in and out. They can also filter out pollutants.
An energy exchanger recovers heat or cold from outgoing stale air to moderate the temperature of the incoming air, saving energy. Outside air is brought in, filtered, and then pre-warmed or cooled before circulating through the home. Stale and moist air from activities like cooking, showering, or even smells from new furniture, is exhausted out.