With more emphasis on energy conservation and efficiency, new home construction can create a problem of indoor air pollution. Vapor barriers, thermal windows, weather-stripping, limit energy loss and also inhibits air-exchange which has a negative effect on internal air quality. Cooking, aerosol sprays, cleaning agents, paints, even excess humidity and mold - if the house is sealed too tightly. Keeping windows or doors open does not conserve energy. A device known as an air-to-air exchanger is used to recover heating or cooling and improve air quality.

There are many different designs of air exhangers, depending on the manufacturer, but the principle is the same. Fresh air is drawn in from a port open to the outside of the building, and passed through a chamber, also know as the exchanger, that is surrounded by indoor air. Highly conductive metal or other materials removes the energy (heat) from the warmer air and gives it to the cooler air. The fresh air is then ducted into the house, and the indoor air is ducted to a port and expelled outside. Up to 80% of the energy can be exchanged. During the energy exchange, moisture (humidity) can condense into water. A drain pan inside the cabinet will allow the water to be collected for removal. If the unit is installed in the basement, a condensate pump might be used to eject the water outside.