systems for space heating became realistic in temperate and colder climatic zones. As heat demand reduces, the overall size and cost of the system is reduced, and the lower water temperatures typical of solar heating may be more readily used - especially when coupled with underfloor heating or wall heating. The volume occupied by the equipment also reduces, which also increases the flexibility of its location. In common with other heating systems in low-energy buildings, system performance is more sensitive to the number of occupants, room temperature and ventilation rates, when compared to regular buildings where such effects are small in relation to the higher overall energy demand. See also Geothermal heat pump Renewable heat concentrating solar (used in these systems to produce heating and not to make electricity) Renewable energy Solar cooling Solar heating Central solar heating Solar thermal energy External links IEA SHC Task 26 official site The European Altener Programme Project: Solar Combisystems Test of Thermal Solar Systems for Hot Water and Space Heating (June 2004) Interseasonal Heat Transfer integrates solar thermal collection and thermal storage Combisystem test reports - Mostly in German References Solar Heating Systems for Houses – A Design Handbook for Solar Combisystems, James and James, (by the Task 26 team) Footnotes Geothermal energy Solar power Solar thermal energy Heating, ventilation, and air conditioning Residential heating