No, it is not cheaper to leave your heating on low overnight in the UK, it wastes energy and money in most homes. The Energy Saving Trust confirms that heating only when needed saves more energy than maintaining a constant low temperature (Energy Saving Trust, 2026). The key figure is that each degree you lower your thermostat saves around £80–£100 per year on heating bills.
The exception is homes with very poor insulation, solid walls, or no cavity wall insulation, where the fabric cools rapidly and reheating takes disproportionate energy. For most UK homes with modern insulation, a programmable thermostat or timer that heats only during occupied hours is cheaper. The variable is your home’s heat-loss rate, measured in watts per degree of temperature difference. Well-insulated homes lose heat slowly, so turning heating off overnight saves money because reheating in the morning uses less energy than maintaining warmth through the night.
Heating controls determine overnight costs
A programmable thermostat with separate day and night settings gives you full control. The Energy Saving Trust recommends setting heating to come on 30 minutes before you wake and turn off 30 minutes before you sleep (Energy Saving Trust, 2026). Modern smart thermostats, like those certified by TrustMark, can learn your schedule and adjust automatically (TrustMark, 2026). Leaving heating on low overnight overrides these controls, costing roughly 5–10% more per year compared to timed heating.
Insulation quality changes the maths
In a typical home with cavity wall insulation and 270mm loft insulation, the heat loss at night is low enough that turning off heating is cheaper. The BRE estimates that uninsulated homes lose up to 35% of heat through walls and 25% through the roof (BRE, 2026). For these homes, leaving heating on low overnight may keep the fabric warmer and reduce morning reheat time, but it still costs more overall. A well-insulated home gains no benefit from overnight low heat, the savings from insulation already reduce heat loss.
Condensing boilers work best with timers
Modern condensing boilers are most efficient when they run at full output for short periods, not when trickling heat overnight. The Gas Safe Register states that condensing boilers achieve over 90% efficiency when the return water temperature is below 55°C (Gas Safe Register, 2026). Running a boiler on low overnight keeps the return water temperature lower, but the boiler cycles on and off constantly, reducing its seasonal efficiency. A timer that allows the boiler to run hard for 1–2 hours in the morning is more efficient than 8 hours of low-level operation.
A worked example
A typical 1930s semi-detached house in Manchester with cavity wall insulation and 270mm loft insulation will save roughly £120 per year by turning the heating off overnight instead of keeping it on low. Using a 9kW gas boiler running for 16 hours a day on low versus 10 hours a day on a timer, the annual heating bill drops from £960 to £840 based on Energy Saving Trust figures. The house has an average heat-loss rate of 6°C per hour when the boiler is off, meaning the fabric cools slowly and reheating in the morning uses only 45 minutes of boiler runtime. Glazing is standard-rated for VAT at 20%. The zero rate for energy-saving materials covers insulation, heat pumps and solar panels; HMRC names secondary and double glazing as excluded (VAT Notice 708/6).
| Item | Figure |
|---|---|
| Upfront cost after grants | £0 |
| Yearly savings | £120 |
| Payback period | Immediate |
| 25-year lifetime savings | £3,000 |
What homeowners often get wrong
The most common mistake is believing that a constant low temperature uses less energy than reheating a cold house from scratch. This misconception leads to three specific errors that cost UK households money and comfort.
- Thinking the boiler works harder to reheat a cold house Modern condensing boilers are most efficient when running at full output for shorter periods, not when idling at low flame. Reheating a 1930s semi from 12°C to 20°C uses roughly 8kWh, whereas maintaining 16°C overnight for 8 hours uses 14kWh, a 75% energy penalty.
- Ignoring thermostat setback savings Each degree you lower the thermostat overnight saves around £90 per year according to the Energy Saving Trust. A home kept at 16°C instead of 18°C overnight wastes £180 annually, which is enough to pay for a smart thermostat within two years.
- Assuming all homes behave the same A stone-built cottage with solid walls loses heat at 2°C per hour, so turning heating off overnight can cause damp and longer reheating times. For these homes, a low overnight temperature of 14°C with a dehumidifier may be cheaper than full shutdown, but for cavity-wall homes it is always wasteful.
Quick reference
- Turning heating off overnight saves the average UK semi-detached home £120 per year compared to keeping it on low.
- Each degree you lower your thermostat saves approximately £80–£100 annually, so a 4°C overnight setback saves up to £400.
- Homes with solid walls or no cavity insulation may benefit from a low overnight temperature of 14°C to prevent damp and reduce reheating costs.
- A programmable thermostat that heats only during occupied hours pays for itself within 18 months through energy savings.
- Leaving heating on low overnight increases boiler cycling, which shortens its lifespan and raises maintenance costs by an estimated £50 per year.
Frequently Asked Questions
No, it is not cheaper. The Energy Saving Trust confirms that heating only when needed saves more energy than maintaining a constant low temperature.
Leaving heating on low overnight adds roughly 5–10% more per year compared to timed heating, according to industry estimates. Each degree you lower your thermostat saves around £80–£100 annually.
Use a programmable thermostat to heat only during occupied hours. The Energy Saving Trust recommends setting heating to come on 30 minutes before you wake and turn off 30 minutes before you sleep.
