A central water heater takes care of two circles of central heating (a new one for below-the-roof rooms, an older for the ground level) and tap water heating. (A solar water heater is linked to it, does all the water heating in summer, but that's no more useful in the heating season.) The heater is regulated by a programmable thermostat in the main room, elsewhere the radiators have thermostats.

The building was re-insulated before we moved in, but it wasn't well done in some places. I note that in this region, it was custom to build houses with multiple windows that open separately, so the critical point is not the glass but the edge of window frames. As for two of our Velux double-glazed roof windows. Also, one room is above the (unheated) garage, with non-insulated floor. Still, even in this room, temperatures fall only 2-3°C through one frosty night even if there is no heating.

I am surprised at how cold homes some of you live in.

The standard figure I learnt is 21°C day/19°C night. As for too much,  I know some people who prefer 26°C at home, which I don't like even on brief visits. Presently I'm set for 20°C day/17-18°C night in the winter. However, I lived through last winter with a bad central heating (the new circle was connected the wrong way, thus hot water rose up along the first tube in the radiators and barely heated, the heat conducted by the floor from the ground-level rooms probably counted more), with temperatures of 18°C day/15°C night when it was sub-zero outside -- and that for weeks and months definitely wasn't comfortable, I felt my joints, and sinuses. (I once slept in 2°C, but that was one night.)

_{*Lunatic*, n.
One whose delusions are out of fashion.}