Abstract: A space heater for small rooms, e.g. house trailers or ship's cabins, comprises an undulating heat exchanger centered on a vertical axis and a combustion pipe surrounded thereby. A burner enters the lower end of the combination pipe whose upper end is closed except for a number of lateral openings communicating with outwardly closed smoke channels of the undulating heat exchanger which alternate with outwardly open air channels. An outer peripheral wall, spacedly surrounding the heat exchanger, forms with its air channels an annular conduit for the conveyance of ambient air entering that conduit near its bottom and leaving it at its top.