Martin Lewis settles your heating dilemma: leave it on low all day or not? 7 tips and £1,755 hit

Harriet Pemberton • April 28, 2026 02:08

Across the UK, plenty of households are weighing up the same question each winter: is it cheaper to run the heating gently all day, or to switch it on for a few targeted bursts when you’re actually at home? With typical annual bills hovering around £1,755 this autumn, the answer matters more than ever - and it’s a topic Martin Lewis has returned to repeatedly over the years.

What Martin Lewis (MoneySavingExpert) says about heating: “always on” vs timed use

Martin Lewis, speaking via MoneySavingExpert, has been clear and consistent: warm your home to match when you need heat, not because the calendar has ticked into November. In practical terms, that means relying on your timer and thermostat - rather than letting the boiler trundle along from early morning until bedtime out of habit.

Heat the home when you’re in and feeling cold, not when the place is empty. Let the thermostat and timer lead - not routine.

Applied properly, the idea is straightforward: pick a comfortable temperature, then programme your heating so it runs mainly during the times you’re generally awake and at home. If everyone is out at work or school for most of the day, there’s little value in paying to heat rooms that nobody is using.

For the majority of properties with average or decent insulation, the “on when needed, off when not” approach usually consumes less gas or electricity than keeping radiators mildly warm 24/7.

Setting your thermostat: finding the comfort “sweet spot”

A room thermostat and a programmer are built to hold a stable temperature without cooking the place. They cycle the boiler on and off to maintain your set level. Crucially, you don’t pay because the system clicks on more often - you pay for the total heat energy delivered over the day.

Many homes settle around 18°C to 20°C in occupied living areas. Spaces such as bedrooms and hallways can often be kept cooler. When you’re out, a modest “setback” temperature - typically around 14°C to 16°C - can prevent the structure getting uncomfortably cold, which may reduce the amount of energy needed to bring it back up to temperature later.

TRVs (thermostatic radiator valves): heat the rooms you use, not the whole house

Thermostatic radiator valves (TRVs) give you more precise control by room. They make it easier to keep spare rooms cooler and concentrate warmth where you actually sit, work and relax. This helps avoid a common wasteful pattern: overheating the entire house just to take the edge off one chilly room.

Why turning the thermostat up doesn’t warm the house faster

A persistent myth is that setting the thermostat to 25°C will heat your home more quickly. It won’t. The thermostat is simply a target temperature; the boiler will heat at its normal rate until that target is reached, then switch off.

So if you want 19°C, set 19°C. Dialling up a higher number usually just makes the system run for longer and risks overheating, which wastes energy. If rooms are taking ages to warm, the likely culprits are insulation, radiator sizing, system balancing, or boiler settings - not the number on the thermostat.

When keeping the heating on low all day can be the better option

The case for low, continuous heat most often comes from people in older, colder or damp-prone homes. Where walls, windows and furnishings get very cold during long “off” periods, the property can feel clammy and may be more vulnerable to condensation.

Properties with single glazing, solid walls, or clear damp issues can lose heat so rapidly that they feel permanently cold after each long off spell.

In these conditions, maintaining a gentle background temperature can help keep surfaces above the point where water vapour turns into droplets. That may reduce mould risk and the miserable “wet cold” effect where 17°C can feel closer to 12°C.

This isn’t a magic trick that defeats physics. Whether it helps depends on how draughty your home is, the level of insulation, and how well ventilation is managed. If you can draught-proof doors and windows, improve loft or wall insulation where feasible, and use extractor fans properly, many households can still run timed heating without suffering the downsides of a freezing building fabric.

Condensation, ventilation and the building “fabric”

Condensation forms when warm, moisture-laden air meets a cold surface. Everyday activities - showers, cooking, drying clothes indoors and even breathing - add water vapour to the air. When that moisture hits a cold wall or window, it turns into droplets.

Breaking the cycle usually needs two things working together: controlled warmth and deliberate ventilation. Short, intense bursts (open windows wide for a few minutes), running extractor fans on a higher setting, and keeping trickle vents open can shift damp air out without dumping all your heat.

In homes where mould appears most winters, many specialists recommend a low but steady background temperature, combined with timed “top-ups” in the rooms you live in. The aim is to keep surfaces slightly warmer so moisture is less likely to settle and feed black mould.

What the “always on” debate means with bills near £1,755

Under the energy price cap, a typical dual-fuel household paying by direct debit faces an annual bill of around £1,720, rising to roughly £1,755 for October to December, based on average consumption. Your real cost still hinges on how long the heating runs and the temperatures you choose.

Even on a low setting, leaving heating on all day can rack up kilowatt-hours if your home keeps bleeding heat to the outdoors - those small amounts still accumulate on the meter. For many households, the most reliable savings come not from sitting in multiple jumpers, but from controlling when and where heat is used.

Timed bursts vs low all day: a side-by-side comparison

Approach	Best suited to	Main drawback	Key controls
Timed heating at a set temperature	Most homes with average or good insulation	Can feel slow to warm up if the setback is too low	Programmer, room thermostat, TRVs
Low-level heat all day	Homes with condensation, damp, or very cold walls	Can increase overall gas use if the temperature is set too high	Low thermostat set-point, ventilation, humidity monitor

Seven practical tips from the Martin Lewis playbook to cut waste

Set a timer so heating follows your routine rather than running 24 hours a day.
Aim for roughly 18–20°C while you’re in, and use a modest 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 rooms warm evenly, instead of turning the thermostat up to compensate for one cold area.
Keep radiators free from obstruction (sofas, heavy curtains, or clothes-drying racks can trap heat).
Seal obvious draught points such as letterboxes, keyholes, window gaps and skirting.
Ventilate with intent: use bathroom and kitchen extractors and short window “purges”, rather than leaving windows on the latch all day.

Small adjustments that can shave pounds off: boiler flow temperature and TRVs

One of the biggest efficiency levers is the boiler flow temperature, yet many people never touch it. Older settings are often left at 70°C+. At those temperatures, modern condensing boilers can’t condense as effectively, which means you miss out on potential savings.

Dropping the flow temperature to around 55–60°C allows the boiler to recover more heat from the exhaust gases. In homes with suitably sized radiators, this can cut fuel use without making the house feel colder. It’s best tested on a milder day first; if the home struggles to reach temperature, edge the flow setting up gradually until you find a sensible compromise between comfort and cost.

TRVs remain an underused money-saver. Keeping lesser-used rooms a few degrees cooler, closing doors to hold warmth in the main living spaces, and adjusting one room at a time creates a simple “zoning” effect that reduces overall demand while keeping you comfortable where it matters.

Smart controls and monitoring (extra ways to improve results)

If you have a smart thermostat or smart TRVs, you can often tighten the same strategy even further. Features like geofencing, schedules by room, and learning routines can prevent the heating running longer than needed. Some systems also provide clear runtime reports, which can help you spot waste you’d otherwise miss.

It can also be worth using a smart meter (or taking regular manual readings) alongside a simple indoor thermometer. Small tweaks - for example, trimming the set-point by 1°C or shortening an evening heating window - become easier to judge when you can see the effect on consumption.

If your home is damp, draughty, or both

For those in older terraces, basement flats, or properties where mould is already visible, the decision is often less clear-cut. A steady background level of roughly 16°C to 18°C, with short boosts at the times you’re at home, can improve comfort and help protect the building fabric.

Moisture management is essential alongside heating. Use bathroom and kitchen fans during and after cooking or showering, and avoid drying laundry in unventilated rooms. A low-cost digital humidity monitor can show whether changes are working - a common target is around 40–60% relative humidity.

Drier walls feel warmer at the same temperature, so reducing moisture can mean you’re comfortable at a setting that’s 1–2°C lower.

Quick checks to do before the first proper cold snap

A handful of basic checks can reduce the chances of expensive surprises once temperatures drop. If your boiler service is due, book it in. Check system pressure if applicable, and confirm radiators warm evenly from top to bottom. Stiff valves, unusual pump noises, or radiators cold at the top can all indicate the system needs attention.

You can also run a simple at-home comparison. Take gas and electricity readings on a “normal” day, then tighten your heating schedule and introduce a modest setback and take readings again on a similar day. Even a 5–10% reduction across October to December can soften the impact of a typical bill drifting towards £1,755.

Scenarios to help you choose the best approach

Imagine a couple in a modern, well-insulated semi-detached home. They’re out from 8 am to 6 pm on weekdays. In many cases, timed heating - for example 6–8 am and 5–10 pm at 19°C, with a 15°C setback in between - will usually cost less than leaving the heating on low all day, while still keeping the home comfortable.

Now consider a ground-floor flat with single glazing and black mould appearing in corners. Here, holding a constant 17°C background and adding short morning and evening boosts may increase gas use slightly, but it can substantially reduce condensation and related health risks - especially when paired with disciplined ventilation. In this case, the priority may be safety and preventing long-term damage, not just shaving pennies.