It is very profitable to use thermal controllers on each radiator, in each room. With their help, you can reduce the temperature in the room when there is no one at home, to the minimum possible (so that the water in the pipes does not freeze, flowers in pots, etc. p. However, it will be more difficult to save here — after all, it will be necessary to put the heat meter on the output and exit of the heating pipe, and in the apartments of Soviet buildings, the risers go in each room, and not the ring around the apartment. Typically, equipment for each apartment pays off separately in 2-3 years.