1200sf, midblock rowhouse, old radiators with a tankless hot water system - about $100, massive improvement (at least $100 less with similar weather) from our old standard tank + boiler with legit visible flames. Keep the house at 67 during the day and just turn them off at night... ymmv if you don't like a chilly room with good blankets! They're programmed to turn on shortly before we get up and so no issue with a freezing breakfast.