Is It Cheaper to Leave the Heating On Low All Day? A Retired Gas Engineer Answers

Summary

Graham, a retired gas engineer with 40 years’ experience, explains whether homes with gas boilers and radiators save money by leaving the heating on low all day.

Main answer and why

• For most homes with gas boilers, leaving the heating on all day usually uses more energy and costs more than using a timer to heat the home when it is needed.
• A warm house continually loses heat through its walls, roof, floor, windows, and gaps. The greater the difference between indoor and outdoor temperatures, the faster heat escapes.
• Graham compares this to a hot cup of tea: it cools quickly at first, then more slowly as it approaches room temperature. A house also loses heat more slowly as it cools.
• Turning the heating off when nobody needs it allows the house to cool and reduces heat loss. Reheating it later uses gas, but that gas replaces heat lost while the home was cooler. Keeping the boiler on continuously also replaces lost heat—just gradually throughout the day and night.
• For example, if it is 5°C outside and the thermostat is set to 20°C, the temperature gap is 15°C. If the home cools to 15°C while nobody is there, the gap is 10°C, so heat may escape at roughly two-thirds the earlier rate. This is only an illustration; actual cooling and savings depend on the home’s insulation, construction, windows, and draughts.

How to apply the advice

• Use the timer and room thermostat: Schedule heating for the times people need it, and let the thermostat prevent the home from getting warmer than the set temperature.
• If you are home most of the day: Heating the rooms you are using is reasonable. The timer can still save energy overnight and whenever the home is empty.
• Know the difference between controls: Lowering the room thermostat reduces the target temperature. The dial on the boiler controls the water temperature sent to radiators, which is a different setting.
• Avoid letting regularly used rooms become too cold: The NHS guidance cited in the video recommends aiming for at least 18°C in rooms used regularly, if possible. Increase the temperature if that is not warm enough for you.

When warmth should take priority

Graham says comfort and health matter more than the bill in some circumstances:

1. If you are vulnerable to cold or have a health condition: The NHS identifies people aged 65 and over, people with long-term conditions or disabilities, and people on low incomes as more vulnerable. If 18°C feels too cold, turn the heating up. The video also advises checking whether financial help is available.
   • Shivering, slurred speech, unusual tiredness or confusion, and pale, cold skin may indicate hypothermia. Call 999 if you think someone has hypothermia, or NHS 111 if you are unsure.
2. If cold conditions contribute to damp: Keep spare rooms at a low temperature rather than leaving them completely unheated, and allow damp air to escape. If mould keeps returning in a rented home, tell the landlord. The video cautions that leaving all the heating on solely to prevent damp can waste energy and money.
3. During a cold snap: Give the home more time to warm up by setting the heating to come on earlier and go off later, rather than simply turning the thermostat higher.
4. In some particular homes: Longer, lower heating may suit very energy-efficient homes, homes with large radiators or underfloor heating, or homes with weather-compensation controls. Graham notes this may not suit a typical gas boiler with radiators used for only a few hours a day. Ask an engineer at the next boiler service if you are unsure.

Getting a warm-home feeling without heating an empty house

• Set the timer to start before you get up; the Energy Saving Trust’s suggested starting point is about half an hour beforehand. Adjust it earlier if needed.
• If the timer permits, set separate heating periods: turn it off while you are out, then have it come on shortly before you return.
• A programmable thermostat may offer a minimum or “floor” temperature for periods when you are away or asleep. Graham presents this as a safety net rather than a reason to run the heating all day.
• Heat the rooms you use. Turn radiator valves up in those rooms and down in rooms used less often, but keep the latter low rather than necessarily turning them off.
• Draw curtains at dusk, keeping them clear of radiators. Shut the door of the room you are occupying to retain warmth, but open doors for a while each day so air can circulate.
• Wear several thinner layers and avoid sitting still for long periods. These measures complement a warm room; they are not a replacement for adequate heating.

Testing your own usage and safety

• Compare a day using the timer with a day when the heating is left on, ideally choosing days with similar weather.
• A smart meter can help. With a standard gas meter, take readings at the same time each day. Treat the result as a rough comparison because visitors, baths, and cooking also affect gas use.
• If the heating does not respond properly to the timer or thermostat, contact a plumber or heating engineer. Never remove the boiler casing to change a setting; work inside the casing must be done by a Gas Safe registered engineer.

Overall: For most gas-boiler homes, timed heating is cheaper than keeping the heating on low all day. Let the home cool when heat is not needed, but keep health and comfort central, use appropriate temperatures in occupied rooms, and adjust the schedule during cold weather.

Speakers and sources featured

• Graham — The video’s presenter and only speaking voice identified in the subtitles; a retired gas engineer.
• Energy Saving Trust — Cited on gas-heating costs, comfort and health, damp, and timer settings.
• Which? — Cited on heating empty rooms and on homes where longer, lower heating may or may not suit.
• Open University — Cited for the explanation of heat loss in buildings.
• NHS — Cited on vulnerable groups, room temperatures, and hypothermia.
• Met Office — Cited on cold weather, health, and heating schedules during cold snaps.
• Nest — Cited in the subtitles for advice about prioritising rooms to heat.