When I was in Bulgaria my family installed heating. It was only in one room yet I said "This is good because we can stay in the same room during the daytime [on the weekends] and save money on our heating bill during winter months."
Now that I look back on it. It makes more sense to heat one room instead of heating three rooms.
(This was many years ago.)
Curtains-Joe
In a very well insulated building it can actually be less energy intensive to heat unoccupied rooms a little to stop them taking too much heat away from other rooms.