F24D—DOMESTIC- OR SPACE-HEATING SYSTEMS, e.g. CENTRAL HEATING SYSTEMS; DOMESTIC HOT-WATER SUPPLY SYSTEMS; ELEMENTS OR COMPONENTS THEREFOR
F24D5/00—Hot-air central heating systems; Exhaust gas central heating systems
F24D5/06—Hot-air central heating systems; Exhaust gas central heating systems operating without discharge of hot air into the space or area to be heated
F24D5/10—Hot-air central heating systems; 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