On for a few hours in the morning and then again in the evening, and set at about 15, unless DC2 gets at it.
This is not as heroic as it sounds as the thermostat is in the cold and draughty hall, so the other rooms warm up quite nicely. Our bedroom rad is off, though, and the DCs' are meant to be turned down to economy, but I expect DC2 (yes, the one who messes with the thermostat when she thinks I might not notice) has hers up at thermonuclear. She has the warmest room in the house anyway...
I freeze my arse off working at home in the day, and sometimes resort to heating one room only. Old houses: lovely, till the winter bites and the gas bill comes in.