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The short answer
The Energy Saving Trust says that keeping your heating on all the time uses more energy and costs more. For a home with a gas boiler, having the heating come on only when you need it is cheaper.
Why the timer wins
Your home loses heat all the time through the walls, windows and roof. The warmer it is inside compared with outside, the faster it loses heat. If you keep the house warm all day, it's losing heat all day. If you let it cool while you're out or asleep, it loses heat more slowly, so the boiler has less to replace.
Yes, the boiler works harder to warm the house back up, but that extra effort is smaller than the heat you'd have lost by keeping it warm the whole time.
The exceptions
- Heat pumps work best running steadily at a low temperature. If you have one, leaving it on is usually right.
- Underfloor heating responds slowly, so it often makes sense to run it for longer at a lower setting.
- Very cold weather. Setting a low "frost" or setback temperature (around 12 to 16°C) while you're out stops pipes freezing and the house getting too cold to warm up quickly.
- Damp or vulnerable people. If you have condensation problems, or someone at home is elderly or unwell, keeping a steady, comfortable temperature matters more than the small saving.
Getting the timer right
- Set the heating to come on about 30 minutes before you get up or get home.
- Turn it off about 30 minutes before you go out or go to bed. The house stays warm for a while.
- Use a room thermostat at around 18 to 21°C. Each degree lower cuts your heating bill.
Cutting your gas use by just 10% saves about £75.72 a year for a typical home at today's prices. See what your boiler costs to run.
Sources: Energy Saving Trust via Ideal Home, Ofgem typical consumption values, Octopus Energy tariff data.