Across the UK, families are asking the same thing: is it cheaper to keep the heating on a low, constant setting, or blast it for a few hours when you are actually at home? Martin Lewis has tackled this debate for years, and with typical annual bills edging towards £1,755 this autumn, his advice lands with extra weight.
What Martin Lewis really says about the ‘always on’ debate
Martin Lewis, through MoneySavingExpert, has been consistent: you should heat your home based on when you need it, not because the clock says it is 1 November. That means using your timer and thermostat smartly, instead of leaving the boiler rumbling away from dawn to bedtime.
Heat when you are there and cold, not when the house is empty. Let the thermostat and timer call the shots, not habit.
In practice, that means choosing a comfortable temperature, then programming the heating to run only during the hours you are usually at home and awake. If everyone is out at work or school all day, there is little point keeping rooms warm for empty chairs and silent sofas.
For most homes with decent insulation, this “on when needed, off when not” approach typically uses less gas or electricity than leaving radiators lukewarm around the clock.
Finding the comfort ‘sweet spot’ on your thermostat
Room thermostats and timers are designed to keep temperatures stable without overheating. They switch the boiler on and off to maintain your chosen set-point. You are not paying extra just because the heating clicks on a few more times; you are paying for the overall heat delivered across the day.
Many households land on about 18°C to 20°C in living spaces when occupied. Bedrooms and hallways can often sit lower. A slightly cooler, “setback” temperature of around 14°C to 16°C while you are out stops the building getting icy, which can reduce the energy needed to warm it up again in the evening.
Thermostatic radiator valves (TRVs) add another layer of control. They let you keep spare rooms cooler and focus warmth where you actually spend time. That helps avoid the classic mistake: overheating the whole house just to take the chill off one cold room.
When leaving the heating on low all day can make sense
The argument for constant low heat usually comes from people living in older or damp properties. In these homes, long periods with the heating off can leave walls and furnishings cold and clammy, encouraging condensation to build.
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Homes with single glazing, solid walls or obvious damp can lose heat so quickly that they feel perma-chilled after every off period.
In that scenario, a gentle, all-day background temperature can help keep surfaces above the point where moisture turns to condensation. That can reduce mould growth and the “wet cold” feeling that makes 17°C feel like 12°C.
This is not a universal loophole that magically beats physics. It depends on how draughty your property is, how much insulation you have, and how well you manage ventilation. If you improve sealing around doors and windows, insulate lofts and walls where possible, and actually use extractor fans, many households can still stick to timed heating without the downsides of constant running.
Condensation, ventilation and your building’s ‘fabric’
Condensation appears when warm, moist air hits a cold surface. Showers, cooking, drying clothes indoors and even breathing add water vapour to the air. When that vapour hits a cold window or wall, it turns to droplets.
The way to break this cycle is a blend of controlled warmth and fresh air. Short, sharp bursts of ventilation — opening windows wide for a few minutes, using extractor fans on high, and keeping trickle vents open — push damp air out without stripping all the heat away.
In homes where mould shows up every winter, many experts suggest a relatively low but steady background temperature, topped up with timed boosts in living areas. That keeps surfaces a bit warmer, so moisture is less likely to settle and feed black mould patches.
What this debate means for bills nudging £1,755
Under the current energy price cap, a typical dual-fuel household paying by direct debit faces an annual bill around £1,720, rising to roughly £1,755 for October to December. That is based on average use. Your actual cost still depends heavily on how long the heating runs and how high you set the temperature.
Leaving the system on all day, even on a low setting, still burns through kilowatt-hours if the house keeps losing heat to the outside. Those trickles add up on the meter. For most people, the way to cut costs is not sitting in three jumpers, but controlling when and where the heat goes.
Timed bursts vs low all day: side-by-side look
| Approach | Best suited to | Main drawback | Key controls |
|---|---|---|---|
| Timed heating at a set temperature | Most homes with average or good insulation | House can feel slow to warm if setback is too low | Programmer, room thermostat, TRVs |
| Low-level heat all day | Homes with condensation, damp or very cold walls | Risk of higher overall gas use if set too warm | Low thermostat set-point, ventilation, humidity monitor |
Seven tips from the Martin Lewis playbook to cut waste
- Use a timer so the heating matches your routine, not a full 24 hours.
- Keep the main thermostat around 18–20°C when you are home, with a small setback when you go out.
- On condensing boilers, try lowering the flow temperature to about 55–60°C for better efficiency.
- Bleed and balance radiators so all rooms heat evenly and you are not turning the thermostat up to fix one cold spot.
- Keep radiators clear of big sofas, long curtains and drying racks that trap heat.
- Seal obvious draughts around letterboxes, keyholes, windows and skirting boards.
- Ventilate deliberately: use bathroom and kitchen extractors, plus short window bursts, instead of leaving windows ajar all day.
Why turning the thermostat up does not speed things up
One stubborn myth refuses to die: the idea that cranking the thermostat to 25°C warms the house faster. It does not. The thermostat is simply a target. The boiler heats at its usual rate until it hits that set temperature, then shuts off.
If you want 19°C, just set 19°C. A higher number only means the system will run for longer and overshoot, wasting energy. If rooms are painfully slow to heat, that points to issues with boiler settings, radiator size, balancing or insulation — not a low number on the dial.
Small setting changes that can shave pounds off
Boiler flow temperature is a major lever that many people never touch. Traditional systems often leave the factory at 70°C or more. At those levels, modern condensing boilers do not condense efficiently, which means lost savings.
Dropping the flow to around 55–60°C allows more heat to be recovered from exhaust gases. That can cut fuel use without sacrificing comfort in houses with reasonable radiators. Try this on a milder day first. If the home struggles to warm up, nudge the flow slightly higher until you find a balance between comfort and economy.
TRVs are another underused tool. Keep little-used rooms a few degrees cooler, shut doors to hold heat in main living areas, and tweak one room at a time. This small zoning effect keeps overall demand down while you still feel cosy where you actually sit.
If your home is damp, draughty or both
For people in older terraces, basement flats or properties with visible mould, the decision is trickier. A constant background level between about 16°C and 18°C, with short boosts at the times you are home, can make life much more comfortable and protect the building fabric.
Pair that with proper moisture control. Run bathroom and kitchen fans during and after use. Avoid drying laundry in unventilated rooms. A low-cost digital humidity meter can show if your efforts are working — aim for roughly 40–60% relative humidity.
Dry walls feel warmer at the same temperature, so reducing moisture can let you live comfortably a degree or two lower.
Quick checks before the first real cold snap
A few simple checks before temperatures plunge can prevent expensive surprises. Get the boiler serviced if it is due, top up system pressure, and make sure radiators are heating evenly from top to bottom. Stiff valves, noisy pumps or radiators cold at the top are signs that attention is needed.
You can also run a small experiment on your own bills. Take gas and electricity readings for a typical “normal” day. Then reprogram the heating for tighter timing and a modest setback, and record readings on a similar day. If you find even a 5–10% reduction across the October–December quarter, that difference starts to cushion the impact of the typical bill nudging towards £1,755.
Scenarios to help you choose your strategy
Picture a couple in a modern, well-insulated semi. They are out from 8am to 6pm on weekdays. Timed heating from 6–8am and 5–10pm at 19°C, with a setback of 15°C in between, will usually beat an all-day low setting on cost while keeping them comfortable.
Now picture a ground-floor flat with single-glazed windows and patches of black mould in the corners. Here, a constant 17°C background with short boosts early morning and evening might slightly increase gas use, but it can dramatically cut condensation and health risks, especially if combined with disciplined ventilation. The choice is less about penny-pinching and more about safety and long-term damage.