Abstract: The invention relates to a space heating system comprising an air cooled solar collector, a heat store, air ducting, a forced draught mechanism valves, auxiliary heating means and a control system. According to the invention the auxiliary heating means includes a heat pump. The heat pump and heat store are located in a thermally insulated air-tight housing divided into different regions for the evaporator, condenser and heat store. The heating system is operable in a mode in which it circulates air from the heat store to the heat pump evaporator and back in a closed air-tight circuit while simultaneously circulating air from the heat pump condenser to the space to be heated and back. The arrangement minimizes heat loss and defrosting of the heat pump evaporator. The invention also provides air ducting made from seamless lengths of foamed plastics material and provided with a vapor-proof lining.