Should I turn off radiators in rooms I do not use?

The saving is real but smaller than people expect, because heat leaks between rooms through internal walls and doors. The risks — damp, mould, and cold walls in the rooms next door — are also real, and both are avoided by turning down rather than off.

Step by step

1. Work out why the room is unused.A spare bedroom used twice a year is different from a dining room used every weekend. The less often it is used, the more sense turning down makes.
2. Turn down rather than off.Setting a TRV to 1 or 2, or to its frost setting, keeps the room around 10 to 12 degrees. That is enough to avoid condensation and costs very little.
3. Keep the door closed.An unheated room with the door open simply drains heat from the heated part of the house, so the boiler works harder and you save nothing.
4. Watch the external walls.The cold surfaces in an unheated room are where moisture condenses. Check the corners of external walls, behind furniture and around windows after a few weeks.
5. Ventilate it anyway.A cold, closed, unventilated room is the classic mould scenario. Open the window for a few minutes on dry days, or leave a trickle vent open.
6. Keep furniture off the external walls.A wardrobe against a cold external wall in an unheated room creates a still, cold pocket that grows mould reliably.
7. Think about the neighbouring rooms.The shared wall becomes a cold surface for the heated room next door, so that room feels cooler and its heating works harder. This is why the saving is less than the arithmetic suggests.
8. Never turn off in a room with plumbing.A cloakroom, an en-suite or a room with pipework in it needs enough heat to prevent freezing. Frost setting, not off.
9. Reconsider in very cold spells.During a hard frost, bring unheated rooms up a little. The cost is small and the risk of frozen pipework and condensation is much higher.
10. Check the system copes.Closing several radiators raises the pressure and flow through the rest. If the pump starts to whine or radiators knock, the system needs a bypass or rebalancing.

Tips

• Frost setting on a TRV is usually the snowflake symbol or the position just below 1. It holds around 5 to 8 degrees.
• Keep the door shut. An unheated room with an open door is the worst of both.
• Check the room every few weeks in winter for the first year — mould appears slowly and is much easier to catch early.

Common mistakes

• Turning a radiator fully off and closing the door for the winter — The room becomes cold and unventilated, moisture from the rest of the house migrates in and condenses, and mould appears on the external walls and behind furniture.
• Turning off radiators in a room with pipework — An unheated cloakroom or en-suite is exactly where pipes freeze in a cold snap. Frost protection settings exist for this.

If it doesn't work

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