with hot air led through heat-exchange ducts in the walls, floor or ceiling

Full Title

Hot-air central heating systems (district heating systems F24D10/00; central heating systems using heat accumulated in storage masses F24D11/00; air conditioning F24F); Exhaust gas central heating systems > operating without discharge of hot air into the space or area to be heated > with hot air led through heat-exchange ducts in the walls, floor or ceiling