Small single-purpose heating reactors [100 to 400 MW( thermal)] for district heat production would be economically feasible if they could be sited in the immediate vicinity of heat consumption areas. This close urban siting requires that the reactor plant be designed with an objective to make the most severe accidents extremely improbable. When this aim is assumed to be fulfilled, the probability of acute health effects will be insignificant. The expectation values of the potential delayed health effects caused by the collective doses brought about by accidents or normal operation will be very low as well, and will be clearly smaller than the excess mortality due to the other alternatives for district heat production.