The method involves arranging valve in first building radiant tube and supplying portion of the thermal energy contained in the heated gas to the buffer memory (4), for heating of domestic hot water or for heating of second building portion thermally isolated from the first building or second building. The feed and/or return line of the heat exchanger (2) and/or the feed and/or return line of the buffer memory and switchable valves (14,24,26) are fluidically connectable with the feed and/or return line of the solar thermal collector (3). An independent claim is included for arrangement for heating building.