A HRV unit extracts used indoor air from the home. This is usually done in the kitchen, the toilet and the bathroom. In addition to extracting the indoor air, a HRV unit also blows fresh outside air into the home. This is done in a fully energy-efficient way with heat recovery. As air is drawn into and expelled from the house, there is no need for ventilation grilles in the façade. This is referred to as balanced ventilation.
The air in the house is usually warmer than the outside air during the winter period. The HRV unit uses this heat to preheat the freshly supplied outside air. The exchange between warm indoor and cold outdoor air takes place in the heat exchanger. Heat transfer takes place within the exchanger, but the different air cannot mix with each other.