Should I leave the heating on low all day?
The honest answer to the most argued-about heating question, and the two situations where the usual advice is wrong.
- Difficulty
- beginner
- Time
- 15 min
- Read
- 3 min
Short answer
For most homes, heating only when you need it costs less. A house loses heat in proportion to how much warmer it is than outside, so keeping it warm all day means losing heat all day. The exceptions are homes at genuine risk of damp or frozen pipes, and heat pumps, which do prefer steady running.
This argument recurs every autumn and both sides quote an authority. The physics is not actually in dispute; what varies is the house, the heating system and how the household lives, which is why the same answer does not fit everyone.
Step by step
- Understand why timed heating usually wins.Heat loss depends on the temperature difference between inside and outside. A cooler house loses heat more slowly. Letting it cool while nobody is there means less total heat lost, so less to replace.
- Discount the reheating argument.The claim that reheating a cold house costs more than keeping it warm does not hold: the energy to warm it back up is less than the energy lost by holding it warm all day. What is true is that it takes time, which is a comfort issue rather than a cost one.
- Set the timer to reach temperature, not to start.A house takes thirty to ninety minutes to warm through. Set the heating to come on before you need the room warm rather than at the moment you want it, and to go off before you leave or sleep — the residual heat covers the gap.
- Set the thermostat once and leave it.The thermostat sets the target, not the speed. Turning it to 25°C does not warm the house faster; it just overshoots and costs more. Pick a temperature that is comfortable and leave it there.
- Use radiator valves to shape the heat.Turn rooms you do not use down rather than heating the whole house to the same temperature. This saves considerably more than adjusting the schedule, and costs nothing.
- Know the damp exception.A house that gets cold and damp, or has a history of mould, can be better with a low background temperature — around 15°C — maintained through the day. Cold surfaces are where condensation forms, and mould costs more than the heating.
- Know the frost exception.In an empty or barely-occupied property in freezing weather, leave the heating on a frost setting. A burst pipe is enormously more expensive than the gas.
- Treat a heat pump differently.Heat pumps run efficiently at low output over long periods and inefficiently in short hard bursts. With a heat pump, steady low-temperature running genuinely is the right approach — the opposite of a gas boiler.
- Consider how long you are actually out.Turning heating off for eight hours saves meaningfully. Turning it off for forty-five minutes does not, and just makes the house uncomfortable.
- Judge it by your own bills.Houses differ enormously in how fast they lose heat. Try one approach for a fortnight and the other for the next in similar weather, and compare the meter. That is more reliable than any general rule.
Tips
- A degree on the thermostat is worth several percent on the heating bill. Trying 18°C rather than 20°C changes more than any schedule tweak.
- Insulation and draught-proofing change this calculation more than the schedule does, because they change how fast the house loses heat in the first place.
- Smart thermostats that learn how long your house takes to warm up handle the timing better than a fixed schedule, particularly for irregular days.
Common mistakes
- Turning the thermostat up to warm the house faster — The thermostat sets the destination, not the pace. The house warms at the same rate and then overshoots past what you wanted.
- Applying gas boiler advice to a heat pump — Heat pumps are most efficient running gently and continuously. Short hard bursts are exactly what they are bad at.
Questions people ask
Is it cheaper to leave the heating on all the time?
For most homes with a gas boiler, no. A house loses heat in proportion to how much warmer it is than outside, so keeping it warm while nobody is there means losing heat all day. Timed heating costs less.
When is leaving the heating on low actually better?
Where damp or mould is a real problem, where pipes could freeze in an empty property, and with a heat pump — which runs far more efficiently at steady low output than in short bursts.