Ventilating household air is an effective way of eliminating pollutants that tend to build up inside homes due to "weather tight" construction, but unwary ventilation leads to the loss of heat in indoor air. Heat Recovery Ventilators, sometimes called air-to-air exchangers, is a ventilation system that preserves up to 75% of the heat of outgoing air. Furthermore, these units can prevent uncontrolled excess humidity which can lead to discomfort, indoor bacteria and mold growth. We provide units by VenMar and Fantech in our installations.