Because the Air to Air exchanger does not produce heat or cooling, the usual furnace and air conditioner efficiency ratings do not apply.However, the efficiency of temperature transfer between the air coming in, and the air getting exhausted is most important. This transfer can be in the range of 50 to 85 percent and is a critical measure of the economy of the unit. Usually, the slower the blower speed the higher the efficiency because the air has a more time to exchange energy. The amount of electricty consumed by the blower motor should also be taken into account.
Unlike your heating and cooling system, the air to air exchanger should run when the outside temperatures are at their mildest. Running the air exchanger at night during the summer will bring in cooler air than during the afternoon; likewise; running the air exchanger during the day in the winter months will bring in the warmest air.