To prevent frost formation on the heat exchanger, the unit manages an automatic defrost cycle through the unbalance of air flows. The defrost system (optional) consists of a specific device and a software that prevents an excessive drop of the temperature in the exhaust air by slowing down the supply air flow and opening the by-pass damper in the heat exchanger. This device requires pairing with a hot water coil kit + modulating valve or a self-regulating electric heater. The system is guaranteed for external temperatures down to -15°C.