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Our house has FreshAire Air Exchangers from Research Products Corp. These devices list a current draw of 1.4Amps. This is average for most circulating fans, etc.

You can calculate the kWh of any device as follows:

1. If the product does not list Watts, take the Amps listing and multiply times the volts (120 in US, 208 or 240 in many European countries) to get Watts
2. kWh = (Watts * Time in Use) / 1000
3. For monthly use, replace Time in Use with 30 * 24 = 720

Thus our Air Exchanger would use (1.4Amps * 120Volts) * 720 / 1000 = 120kWh in a month. This can translate into $8-$20 a month depending on your cost per kilowatt.

We don't run our exchangers all day. We use a home automation system to turn on the HVAC ciruclating fan and the air exchanger for 30 minute cycles. We usually run it in the morning when everyone is getting ready and/or breakfast is being cooked and at night after dinner. We are also thinking of adding a cycle in teh early morning to give the house a fresh smeel when everyone wakes up. This saves a LOT of energy. It also reduces the frequency of maintenance since constant running of an air exchanger requires frequent cleaning of the washable filters inside. With our light use, we can go 6 months between filter cleanings. If we only run the exchanger 90 minutes a day, we reduce our energy usage to around 7.5kWh. Note this does NOT take into account the energy used by the HVAC system blower, though it is similar.

When determining how long to run your air exchanger, you can go by your nose (i.e. when the hosue smells better), or by using Cubic Feet per Minute calculations. Most Air Exchangers will list their airflow in CFM. Then calculate the Cubic Feet of space in your house. This will tell you how many minutes (in theory) it would take for the exchanger to move all the air in your house outside. Of course the HVAC system is constantly moving that air, but it gives a good starting point.