Martin Lewis: Heating low all day or timed bursts as bills hit £1,755

Across the UK, plenty of households are weighing up the same question: does it cost less to leave the heating ticking over at a low level, or to run it hard for a few hours only when you are actually home? Martin Lewis has been addressing this argument for years, and with typical annual bills drifting towards £1,755 this autumn, his guidance feels even more relevant.

What Martin Lewis really says about the ‘always on’ debate

Via MoneySavingExpert, Martin Lewis has stuck to a clear principle: warm your home when you need warmth, rather than because the calendar says it is 1 November. In other words, use your timer and thermostat effectively, instead of letting the boiler trundle on from early morning until you go to bed.

Heat when you are there and cold, not when the house is empty. Let the thermostat and timer call the shots, not habit.

Put into day-to-day terms, you pick a temperature you find comfortable, then set the heating to run during the hours you are typically at home and awake. If the house is empty all day because everyone is at work or school, it rarely makes sense to keep rooms heated for nobody.

In many properties with reasonable insulation, the approach of “on when needed, off when not” will usually consume less gas or electricity than keeping the radiators gently warm 24/7.

Finding the comfort ‘sweet spot’ on your thermostat

Room thermostats and timers are built to hold a steady indoor temperature without constantly overheating. They cycle the boiler on and off to maintain your set-point. You are not automatically paying more because the heating starts up more often; what you pay for is the total heat supplied over the day.

A lot of households settle around 18°C to 20°C in living areas when they are in use. Bedrooms and hallways can often be cooler. When you are out, a modest “setback” level of roughly 14°C to 16°C can prevent the home becoming bitterly cold, which may also reduce the energy needed to bring temperatures back up later.

Thermostatic radiator valves (TRVs) give you finer control still. They allow you to keep unused rooms cooler while prioritising warmth where you spend your time, helping you avoid a common error: heating the whole house too much just to take the edge off a single chilly room.

When leaving the heating on low all day can make sense

The case for low, constant heating is most often made by people living in older buildings or homes that struggle with damp. In those properties, long spells with the heating off can leave walls and furniture cold and clammy, which makes condensation more likely.

Homes with single glazing, solid walls or obvious damp can lose heat so quickly that they feel perma-chilled after every off period.

Where that is happening, maintaining a gentle all-day background temperature can keep surfaces above the level where moisture turns into condensation. That can help limit mould and reduce the “wet cold” sensation that can make 17°C feel like 12°C.

It is not a universal trick that somehow defeats physics. Whether it works depends on how draughty your home is, what insulation you have, and how well you handle ventilation. If you improve draught-proofing around doors and windows, insulate lofts and walls where you can, and make sure extractor fans are used properly, many households can still rely on timed heating without the disadvantages of running it constantly.

Condensation, ventilation and your building’s ‘fabric’

Condensation forms when warm, humid air meets a cold surface. Moisture is added to indoor air by showers, cooking, drying clothes inside and even breathing. When that vapour touches a cold window or wall, it becomes water droplets.

To stop the cycle, you usually need both sensible warmth and fresh air. Brief, purposeful ventilation - opening windows wide for a few minutes, running extractor fans on a high setting, and leaving trickle vents open - can remove damp air without dumping all the heat.

In homes where mould appears each winter, many specialists recommend keeping a lower but steadier background temperature, then using timed boosts in living spaces. With warmer surfaces, moisture is less likely to settle and feed black mould.

What this debate means for bills nudging £1,755

Under the current energy price cap, a typical dual-fuel home paying by direct debit faces an annual bill of about £1,720, increasing to roughly £1,755 for October to December. Those figures assume average consumption. What you actually pay still hinges on how long the heating runs and the temperature you set.

Even on a low setting, leaving the system on all day still uses kilowatt-hours if the property is continually losing heat outdoors. Small amounts add up on the meter. For most households, the biggest savings come less from enduring the cold in multiple jumpers and more from controlling when and where heat is delivered.

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	Home can take longer to feel warm if the setback is too low	Programmer, room thermostat, TRVs
Low-level heat all day	Homes with condensation, damp or very cold walls	Higher overall gas use if the set-point is too warm	Low thermostat set-point, ventilation, humidity monitor

Seven tips from the Martin Lewis playbook to cut waste

• Set a timer so heating fits your routine, rather than running for the full 24 hours.
• Keep the main thermostat around 18–20°C while you are in, with a small setback when you go out.
• If you have a condensing boiler, consider reducing the flow temperature to about 55–60°C to improve efficiency.
• Bleed and balance radiators so heat is spread evenly, rather than turning the thermostat up to compensate for one cold area.
• Do not block radiators with large sofas, long curtains or drying racks that trap warmth.
• Draught-proof obvious gaps around letterboxes, keyholes, windows and skirting boards.
• Ventilate with intent: use bathroom and kitchen extractor fans, plus short window bursts, instead of keeping windows slightly open all day.

Why turning the thermostat up does not speed things up

A persistent myth is that setting the thermostat to 25°C will heat the home faster. It will not. The thermostat is simply a target temperature. The boiler runs at its normal output until that target is reached, then switches off.

If you want 19°C, set 19°C. Dialling in a higher figure simply keeps the system running longer and can lead to overshooting, which wastes energy. If rooms are taking an age to warm, the likely causes are boiler settings, radiator sizing, balancing or insulation - not that you chose a sensible number on the dial.

Small setting changes that can shave pounds off

One of the most important settings people overlook is the boiler flow temperature. Many systems are set at around 70°C or higher as standard. At those temperatures, modern condensing boilers often do not condense as efficiently, which means you miss out on potential savings.

Reducing the flow to around 55–60°C can enable more heat recovery from exhaust gases. In homes with suitably sized radiators, that can lower fuel use without sacrificing comfort. It is best to test this on a milder day first. If the house then struggles to reach temperature, increase the flow slightly until you find a workable compromise between comfort and cost.

TRVs are also widely underused. Keep rooms you rarely use a few degrees cooler, close doors to retain warmth in the main living areas, and make adjustments one room at a time. This light “zoning” can reduce overall demand while keeping you comfortable where you actually sit.

If your home is damp, draughty or both

For those living in older terraces, basement flats or properties with visible mould, the choice is more complicated. Holding a constant background temperature somewhere between about 16°C and 18°C, combined with short boosts at the times you are home, can improve comfort and help protect the building fabric.

Support that with sensible moisture management. Run bathroom and kitchen fans while you use them and afterwards. Avoid drying washing in rooms without ventilation. A cheap digital humidity meter can help you see whether changes 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 straightforward checks before temperatures drop sharply can help you avoid costly problems. If your boiler is due, book a service, check and top up system pressure, and ensure radiators warm evenly from top to bottom. Stuck valves, loud pumps, or radiators that are cold at the top can all indicate something needs attention.

You can also test what works using your own meter readings. Note your gas and electricity use on a typical “normal” day. Then tighten your heating schedule, add a modest setback, and take readings again on a comparable day. If you see even a 5–10% cut across the October–December quarter, that saving can start to soften the impact of a typical bill edging towards £1,755.

Scenarios to help you choose your strategy

Imagine a couple living in a modern, well-insulated semi. They are out from 8am to 6pm on weekdays. Heating from 6–8am and 5–10pm at 19°C, with a 15°C setback in between, will often cost less than a low all-day setting while still keeping them comfortable.

Now consider a ground-floor flat with single-glazed windows and black mould in the corners. In that case, a steady 17°C background with short boosts morning and evening may raise gas use slightly, but it can significantly reduce condensation and health risks, particularly alongside disciplined ventilation. Here, it is less about penny-pinching and more about safety and preventing long-term damage.

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