Which rooms should I heat and which can I let go cold?

Heating only the rooms in use is one of the few genuinely large savings available, because a large share of most homes is unoccupied most of the time. The catch is that a cold room in an otherwise warm house is exactly where moisture goes.

Safety

Step by step

1. Work out which rooms are actually used.Most households heat a spare bedroom, a dining room and a hallway to the same temperature as the living room, and occupy them for a fraction of the day. That is where the saving is.
2. Turn radiators down rather than off.A thermostatic valve on 1 or 2 holds a room around 15-16°C rather than letting it go fully cold. That is enough to prevent condensation and costs very little.
3. Keep doors closed between warm and cold rooms.Otherwise warm humid air moves into the cold room and condenses on its walls and windows. Closing doors is what makes selective heating work rather than just relocating the problem.
4. Never let a room drop below about 15°C.Below that, external walls get cold enough for moisture to condense on them, and mould follows within weeks. The cost of dealing with mould exceeds the heating saved.
5. Watch the cold rooms for the first month.Check external wall corners, behind furniture, around window reveals and inside wardrobes on outside walls. Any dampness means the room needs to be warmer or better ventilated.
6. Still ventilate the cold rooms.A closed unheated room with the window shut all winter is the classic mould scenario. Open it wide for five minutes every day or two.
7. Prioritise where people sit still.Sitting still needs a warmer room than moving around. A living room where people read in the evening genuinely needs more than a kitchen where someone is cooking.
8. Think about bedrooms separately.Bedrooms are generally comfortable cooler, around 16-18°C, and better ventilated. That is one of the easiest reductions with no loss of comfort.
9. Balance the system if some rooms overheat.If turning down some radiators makes others scorching, the system needs balancing at the lockshield valves. It is a slow but free adjustment.
10. Do not turn everything off when away.Leave a frost setting or a low background temperature. Coming home to burst pipes is the failure mode that erases years of savings.
11. Draught-proof the cold rooms too.A cold draughty room pulls air through the whole house, so its draughts cost you in the rooms you are heating as well.

Tips

• A cheap thermometer in each unheated room takes the guesswork out and shows quickly whether 15°C is actually being held.
• Thermostatic valve numbers are not temperatures, but on most valves setting 2 corresponds to roughly 16°C and setting 3 to roughly 20°C.
• Heating a smaller area well is usually more comfortable than heating the whole house inadequately, and costs less.

Common mistakes

• Turning radiators fully off in unused rooms — The room drops cold enough for moisture to condense on external walls, and mould appears within weeks. Turn down, not off.
• Leaving doors open between heated and unheated rooms — Warm damp air flows into the cold room and condenses there. Selective heating only works with the doors shut.

If it doesn't work

Questions people ask