The thermostat is the cheapest energy-saving tool in the house, because it costs nothing to use and controls the biggest bill you have. Used well it saves real money; used out of habit it quietly overspends, heating empty rooms and sleeping houses to daytime warmth. This guide covers the right temperature to set, how to time the heating to your day, using the room thermostat and radiator valves together, and the truth about leaving the heating on low all day.
The short answer. Set the thermostat to the lowest temperature that is genuinely comfortable, often somewhere in the high teens to around 20C for a living room, and turn it down a degree to save without really noticing. Time the heating to come on shortly before you get up and home, and drop back when you are out or asleep. Use radiator valves to turn down rooms you do not use. Despite the myth, leaving the heating on low all day costs more for almost everyone, not less.
The right temperature: every degree counts
Every degree on the thermostat counts. Dropping the temperature by one degree trims a noticeable slice off a heating bill, commonly £60 to £100 a year, and is barely perceptible day to day, especially with a jumper on. The reason is that a warmer house loses heat to the outside faster, so it takes more energy to hold a higher temperature against the cold outside.
A living room is comfortable for most people somewhere in the high teens to around 20C. Bedrooms and hallways can be cooler. Set the thermostat to the lowest temperature that is genuinely comfortable, not the highest you can afford. There is no fixed correct number, because comfort depends on draughts, humidity, how active you are and what you are wearing, but pushing the setting up out of habit is where a lot of money leaks away.
If parts of the house feel cold at a sensible thermostat setting, the answer is usually to stop the heat escaping rather than crank the dial. Draught-proofing, heavier curtains and loft insulation let you feel warm at a lower setting. Our guide to what temperature should I set my thermostat goes into the comfort side.
Time it to your life
There is no sense heating an empty house or a sleeping one to daytime warmth. Use the programmer or a smart thermostat to bring the heating up shortly before you get up and home, and let it drop back when you are out or in bed. This timing, matching the heat to when you are actually there to feel it, is where a lot of the saving hides.
A simple, effective pattern for a typical working household is two heating periods: a warm-up before you wake, off through the working day, then back on before you return and off again overnight, with the temperature falling back rather than to zero so the house never gets stone cold. Set the warm-up to start half an hour or so before you need the room warm, since the house takes time to reach temperature.
A smart thermostat handles this without you thinking about it, and the better ones learn how long your house takes to warm up and can hold off heating an empty house using your phone's location. They are not essential, though: a basic programmer set thoughtfully captures most of the benefit for nothing.
Room thermostat and radiator valves together
The room thermostat controls the whole system; thermostatic radiator valves control each room. Used together they let you heat where you live rather than the whole house equally.
Set the main thermostat for your main living space, the room you spend the most time in, and turn the radiator valves down in rooms you rarely use, like a spare bedroom. The boiler then has less radiator surface to feed in those rooms, so it burns less gas and the rooms you use reach temperature faster. This is zoning on a budget, and the trade-offs are set out in is it cheaper to heat one room or the whole house.
One caution: do not turn unused rooms stone cold all winter. A radiator valve set to frost protection or a low number keeps the room ticking over, which avoids condensation and mould on cold outside walls. Putting that right costs far more than the heating you saved, so keep unused rooms gently warm rather than off. The broader picture of one-room versus whole-house heating is in is it cheaper to heat one room or the whole house.
On low all day, or off when out?
A persistent myth says it is cheaper to leave the heating on low all day than to heat the house only when you need it. For almost everyone it is not. A well-timed system that heats the house when occupied and lets it cool when empty uses less than one trickling away around the clock.
The logic is simple. A house loses heat at a rate that depends on the difference between inside and outside temperature. Let the house cool while you are out, and that gap shrinks, so it loses less heat during those hours. Heat it back up when you return, and you have spent less in total than holding it warm all day. Heat a house you are in, not one you are not.
The one genuine exception is a very well-insulated home, where the temperature barely drops over a few hours anyway, so there is little to gain from letting it cool. Even then, leaving it on low is at best no cheaper, not actually cheaper. Our full piece on leaving the heating on all day works through the numbers, and it is one of the most common energy saving myths.
What good thermostat habits save
None of these moves costs anything beyond an optional smart thermostat, yet together they take a real bite out of the largest bill in the house. Here is the rough scale at current gas prices for a typical three-bed home.
| Habit | Cost | Typical annual saving |
|---|---|---|
| Turn thermostat down 1C | Free | £60 to £100 |
| Time heating to occupancy | Free | £50 to £150 |
| Zone with radiator valves | £10 to £20 per valve | £30 to £80 |
| Stop leaving it on low all day | Free | £50 to £120 |
At 7.33p per kWh gas, Ofgem cap July to September 2026. Savings are typical ranges and depend on your house, insulation and how cold the winter is. Worked examples; check your own bills.
Because the thermostat governs the heating, and heating is the biggest energy cost in most homes, getting these habits right is the highest-value free change you can make. Do them before spending on kit. The wider order of attack is set out in the heating overview, and for a seasonal check-up see the winter energy checklist.