ERV/HRV Sizing Calculator

How It Works

ERVs (Energy Recovery Ventilators) and HRVs (Heat Recovery Ventilators) are balanced ventilation systems that bring in fresh outdoor air while exhausting stale indoor air — and recovering most of the energy in the process. An HRV transfers heat only: in winter, the warm outgoing air heats the cold incoming air through a heat exchanger, recovering 70 to 85 percent of the energy. An ERV does the same but also transfers moisture, which is important in humid climates where you want to prevent outdoor humidity from entering, or in very dry climates where you want to retain indoor moisture. ASHRAE Standard 62.2 specifies the minimum ventilation rate as 0.01 CFM per square foot of floor area plus 7.5 CFM per occupant (estimated as bedrooms plus one). Modern tight homes with low natural infiltration benefit most from these systems. The energy recovery typically pays for the operating cost of the fan, making fresh air essentially free from an energy standpoint.