As the heating goes back on for the colder months, it is tempting to switch off the radiator in the spare bedroom or the dining room nobody uses. In most homes the better answer is to turn it down, not off. A little background heat in every room saves most of what you hoped to save, without the damp, mould and frozen pipes that a fully cold room can bring.
Below we cover how your valves work, why a cold room causes problems, the settings to use instead and when to get your system checked. Everything here is done by hand at the valve, never inside the boiler casing or the pipework.
Why turning a room down usually beats turning it off
A cold room does not sit on its own. Heat from the warm rooms around it leaks through shared walls, so the saving is usually smaller than people expect.
The bigger problem is moisture. Everyday cooking, showers and drying clothes fill the house with damp air, and that air drifts into the cold room. When it meets cold walls and windows it turns back into water, which is called condensation. Over a winter, that means mould on window frames and damp behind furniture. The Energy Saving Trust advises keeping some background heat in rooms you use less, partly to cut the risk of condensation and mould.
Know which valve you have
A thermostatic radiator valve, or TRV, is the dial with numbers on it, usually from 1 to 5 or 6, often with a snowflake symbol below 1. It senses the air temperature around it and lets more or less hot water into the radiator to hold the room at that setting. The numbers are not exact temperatures and vary between makes, but a lower number always means a cooler room.
A manual valve is a plain wheel or cap with no numbers. It can be open, closed or part open, but it cannot hold the room at a set temperature.
At the other end there is usually a lockshield valve, often hidden under a plastic cap. It sets each radiator's share of the hot water when the system is balanced. Leave it alone. Turning it changes how the whole house heats, and our guide on how to balance radiators for even heating explains why.
Safe settings for a room you don't use
Simple changes you can make yourself:
With a TRV: turn it down to 1 or 2 rather than the snowflake or 0. The snowflake is the frost setting, which only opens the valve when the room gets close to freezing. That is fine for a short holiday, but too cold for a room left empty all winter.
With a manual valve: close it most of the way rather than fully, so a little warm water still runs through the radiator.
Keep the door shut so the room does not pull warmth from the rest of the house, but leave any window trickle vent open so moisture can escape.
Look in every week or so for water on the inside of the windows, damp patches or a musty smell. If you see any of these, turn the valve up a notch.
Keep furniture and radiator covers away from a TRV. Trapped warm air makes the valve close early.
The radiators you should never turn right down
Three radiators need to stay on, however little the room is used. The first is the radiator in the room with your main wall thermostat, usually the hall or living room. Turned down, that room never reaches the thermostat's setting, so the boiler keeps running. It often has no TRV for this reason, or its TRV should stay fully open.
The second is any room with pipes on an outside wall, in the loft or under a suspended wooden floor. A cold room makes those pipes more likely to freeze in a hard frost, and a frozen pipe can split. Our post on how to stop your pipes freezing covers the other steps worth taking before winter.
The third is the bathroom, the dampest room in the house.
What turning rooms down means for your boiler
Most homes now have a condensing boiler, which recovers extra heat from its own exhaust gases and works best when the water returning from the radiators is fairly cool. Turning a few rooms down is fine. Closing most of them leaves the heated water too few places to go, so the boiler can start short cycling, which means firing up and switching off every few minutes, wasting gas and wearing parts. Whistling pipes or a boiler turning on and off far more than usual after closing rooms are signs to have it checked.
Common questions about heating rooms you don't use
Does it matter if my radiators have no TRVs?
Without TRVs you can't hold a room at a set temperature, so leave the manual valve slightly open rather than closed. Fitting TRVs lets you set each room separately.
Should I turn the radiator down when I open a window?
Yes, if the window will be open for more than a few minutes. A TRV near an open window senses the cold air and opens fully, heating the outdoors. Turn it back up when you close the window.
Do smart radiator valves help with rooms I don't use?
A smart valve replaces the TRV head and lets you set a schedule for each room from your phone, so a spare room can sit low and warm up before guests arrive. Not every system suits them, so it's worth checking first.
If you'd like your radiators and controls set up properly before the cold weather, Bog Standard Plumbing and Heating can check your valves, balance your system and advise on room-by-room control. You can book a visit through our central heating service.
