As building codes and programs such as Energy Star and Passive House require higher degrees of air sealing in new construction, the use of heat recovery ventilation (HRV) is increasing. A wide range of HRV products are now available for residential and commercial applications.
Fundamentally, an HRV is an air-to-air heat exchanger. During winter, an incoming stream of cold outside air passes through the heat exchanger core of the HRV where it absorbs heat from the outgoing (but warm) air stream. The amount of heat recovered depends on the temperature differences, but recovery efficiencies in the range of 70% are often cited by HRV manufacturers.