The central appts. heats or cools selectively the heat carrier medium which is supplied to room convectors (10) via feed lines. Each convector comprises a heat exchanger and a fan. The central appts. contains an air-water heat pump (9). The heat carrier medium is water passing through the heat exchangers of the convectors, some of which include a fresh air connecting union. To the air-water heat pump is fed the spent air from the rooms (1-6). Pref. a control member at each convector for mixing the fresh and spent air, and/or switches from one to the other.
