Abstract: The heating system includes water-radiators, a heat source as a boiler and/or one or more water-accumulators, an expansion vessel and a pipe-circulation system interconnecting the radiators and the source through which the water is pumped. The system is intended for one-family-houses with normally at most two floors above a cellar or a basement in which the source is situated. The expansion vessel is contrary to conventional open expansion systems arranged below the levels of the radiators in the boiler room and thus frost-free and immediately above or beside the top of the heat source. Its own top is provided with an open outlet to the atmospheric air in the boiler room. Thus the heat source is exposed approximately only for the very low water-pressure from its own water. Contrary to the heat source the radiators with belonging riser- and return-pipes are exposed to the same high water-pressure as at conventional radiator-systems with the expansion vessel situated above the topmost radiators.