Central heating thermostats like to "Pulse & Glide": they turn on at a certain temperature and keep the heat on until the temp rises a certain amount. Our thermostat has a span of 0.5*C, that is if the temp is set to 19*C then it turns on at 18.75*C and heats until it gets to 19.25*C. Recently I noticed that the span can be set to 1*C, so the boundry temperatures would be 18.5*C and 19.5*C. As far as comfort is concerned, less temperature variation is better, but what about efficiency? If I change the setting, then the "coast" would be much longer, but also the "pulse" would seem to be forever. If the system turns on less often, but for longer, then maybe there would be less losses from the furnace starting up and heating all of that water (we have 250-300 liters of water in the radiators and pipes). Also, the water pump sucks up 100W and is pretty loud, so the less it's on, the better (it's built into the furnace and can't be easily replaced with a more efficient unit
).