The most common defrost strategy employed by manufacturers is known as ‘recirculation defrost’. This strategy temporarily allows the leaving air to be redirected into the incoming air duct to warm it up enough to keep the core from frosting. This cylce is generally 25-75% of an hour, every hour depending on outside temperature. NOTE- that while this is happening - there is no (or very little) fresh outside air coming in. This effectively lowers your fresh air ventilation rate... and turns your mechanical ventilator into a recirculation fan pushing air around for little reason.
UltimateAir has provided a pre-heat - pulse modulated solution that allows for no decrease in ventilation. This is the most efficient solution which ensures the fresh air required for the health of the occupants in the home. This is one of many other methods that best keep the incoming air at or above 12 F.
That is the short of it. Defrost is a fairly complex notion to discuss with regard to the cost associated with it. Know that UltimateAir has your health in mind first.
Contact UltimateAir for more details.