But if the room remains at 19° even when the thermostat is set lower, then the heating will provide the same energy output* regardless of whether it's set at 9°

But if the room remains at 19° even when the thermostat is set lower, then the heating will provide the same energy output* regardless of whether it's set at 9° or 19°; that is, zero. The heat flux through the walls with the neighbours will be the same in either situation, since that depends on the temperature difference, not The previous comment [0] shows the truth of this, if you wanted the room set to 18° you would need to run cooling, which would cost you AND it would increase the neighbour's bills yet again, since now the heat flux is even greater. Given the heating output will be zero whether 9° or 19°... this suggests that what people are reacting to is @kmm's intent... Fair enough in the context of social norms, because with the thermostat set at 9° a non-physics normie would assume they were intending to 'steal' heat, whereas at 19° they are 'contributing fairly'... even when the actual output from their heating is exactly the same. * This all assuming electrical / heat pump heating and an ideal scenario. In the real world there are temperature variations across the room and the idealist model may very well cease to apply. [0] https://news.ycombinator.com/item?id=29288237 https://news.ycombinator.com/item?id=29288237