If the unit has a high-efficiency counterflow heat exchanger (heat exchanger), ice may form in the exchanger during periods of cold weather. This will result in reduced heat recovery and potentially cause a draught in the dwelling at night.
In order to prevent icing of the counterflow heat exchanger during cold periods, it is recommended that you install a pre-heating element for frost protection before the unit. The pre-heating element ensures that the outdoor temperature does not fall below -3 ºC. It regulates in steps to avoid unnecessary energy consumption.