The Danish company Nilan has created a heat pump that is intertwined with the heat recovery of a central ventilation system. The heat that is exhausted, even after heat recovery, is still warmer than the outside temperature in winter. The energy can be used as input for a small heat pump without the need for an exterior unit. This all-in-one system fits in a cabinet and has a peak heating capacity of 1 kW, which can be enough for well designed houses.