Fresh Air Supply for Exhaust-Only Ventilation

Experts agree that controlled mechanical ventilation is key to ensuring good indoor air quality. This is especially true with energy-efficient, tight houses, but even in leaky houses relying on passive ventilation may not be sufficient, particularly on calm, milder days. Under such conditions, the forces that drive air movement through a building envelope are minimal.

Mechanical ventilation systems all use fans to pull air out of the house. Recovering heat from the outgoing air using a heat recovery ventilator (HRV) or air-to-air heat exchanger, is an attractive strategy for saving energy. But HRVs have several problems. First, they are often expensive to install and maintain. Second, they consume significant amounts of electricity because fans are blowing air in two directions across a heat exchange core. And third, some experts argue that because the airflow is