Martin Lewis to chilly households: should you leave the heating on low all day or risk 10% more?

With the mercury set to dip, Britain faces the annual heating dilemma, and one familiar money voice has weighed in again.

As radiators creak back into life, the same question returns: keep the boiler ticking over or only heat when you need it. Martin Lewis has restated his view, and it comes with a crucial caveat for homes that struggle with damp and condensation.

What Martin Lewis actually recommends

Lewis’s guidance remains straightforward. For most households with gas central heating, it usually costs less to heat your home only when required. Leaving the heating on low all day tends to waste energy because heat continuously escapes through walls, windows and roofs. The longer you heat, the more you pay to replace that lost warmth.

For most homes, heating when you need it wins on cost. Let the timer and thermostat do the heavy lifting.

He champions timers and room thermostats. Program heat to come on before you wake and before you return home. Set a comfortable target temperature rather than running the boiler constantly. Thermostatic radiator valves (TRVs) then fine-tune individual rooms, so you avoid paying to heat spaces you barely use.

Why constant low heat costs more in many homes

Heat loss rises with the temperature difference between indoors and outdoors. Maintain a steady warm interior for 24 hours and you keep topping up that loss. Short, timed heating sessions limit the length of that expensive top-up. In a well-insulated property, the building stays warmer between runs, so you need less gas to nudge it back to comfort.

The moisture and damp exception

There is a notable exception flagged by Lewis. Some properties suffer from persistent condensation. When heating stops for long stretches, moisture can soak into cold walls and fabric. That moisture can carry heat away more quickly and encourage mould. In those specific homes, a gentle background setting can help keep surfaces warm enough to reduce condensation, while targeted blasts deliver comfort when you are present.

If your home is prone to condensation, consider a low background setting, better ventilation and short heating bursts.

How to set up your system for cheaper warmth

Timers, thermostats and TRVs

• Use a simple schedule: morning warm-up before you wake, evening warm-up before you return.
• Set the main thermostat between 18C and 20C for living areas; bedrooms can sit lower, around 16C to 18C.
• Fit and use TRVs to keep spare rooms cooler, typically 14C to 16C, and prioritise the rooms you occupy.
• On a condensing gas boiler, reduce the flow temperature to around 55C–60C so it condenses more often and uses less gas.
• Bleed radiators, balance the system and check timers after power cuts or clock changes.
• Smart thermostats can pre-heat efficiently before occupancy and avoid overshooting.

Small changes that stack real savings

• Drop the thermostat by 1C. That can cut space-heating demand by roughly 10% across the season.
• Shut doors between zones. Heat the room you are in, not the hallway.
• Close curtains and blinds at dusk and fix draughts around doors and letterboxes.
• Ventilate bathrooms and kitchens with extractor fans to control humidity without over-heating the whole home.
• Insulate the hot water cylinder and pipework to keep stored heat longer.
• Service the boiler annually so it runs safely and efficiently.

Lowering your thermostat by 1C can trim heating demand by about 10% without a big comfort hit.

Real-world schedules people actually use

Your pattern depends on insulation, occupancy and comfort preference. These examples show how households set timers and setpoints in practice.

What about heat pumps, underfloor and electric heaters?

Heat pumps work best with long runs at low flow temperatures. They like steady-state operation and weather compensation, so a form of continuous, gentle heating can be efficient. That still does not mean 24/7 comfort temperatures. Set back when you are asleep or out, and use room-by-room control if available.

Underfloor heating has slow response. Program it to start earlier and finish later, but avoid very high setpoints. Maintain a modest setback rather than turning it completely off for short gaps.

Portable electric heaters deliver pricey heat per kilowatt-hour. Use them only to top up a single room briefly. Storage heaters should charge on off-peak overnight rates and release heat during the day; learn the input and output controls to avoid wasting charge too early.

A quick energy sketch to frame the maths

Imagine a semi with an indoor target of 19C and an outside day of 5C. The bigger the gap, the faster heat leaks. Run the house at 19C for 24 hours and you pay to replace that leak all day. Run it at 19C only for the hours you occupy, and drop to 15C when you are away or asleep, and you shrink the average temperature difference for a big slice of the day. That reduces total heat loss over 24 hours and cuts consumption.

The numbers vary by insulation and airtightness, but the direction holds. Shorten the hours at higher temperatures, and you often spend less. If you have a condensation problem, pair a mild background setting with better ventilation to control humidity while avoiding needless heat loss.

Shorter heating windows and sensible set-backs reduce the average temperature difference, which reduces total heat loss.

Extra checks before winter bites

• Use a hygrometer to monitor humidity. Aim for 40–60%. Below that feels dry; above that risks condensation.
• Open trickle vents and run extractors in bathrooms and kitchens. Keep lids on boiling pans.
• Seal obvious draughts, but do not block planned ventilation or flues.
• Insulate lofts and cavity walls where possible. Fabric upgrades pay you back year after year.
• Consider weather-compensation or load-compensation controls on modern boilers for smoother, cheaper operation.

What people are actually doing this year

On energy forums, many report using stat-led schedules rather than constant low heat. Typical patterns set living areas to 19–20C during breakfast and evening, with a setback of 14–16C the rest of the time. Those in newer, well-insulated homes often keep summer heating off entirely and rely on short, sharp runs once the chill returns.

Some households that live with damp opt for a gentle background temperature through the day, then ramp up heat during occupied periods. That approach balances moisture control with bill control, especially when paired with extractor fans, trickle vents and regular window airing.

Need-to-know if bills rise again

If unit rates increase, the same rules still save money because they reduce total kilowatt-hours used. Prioritise controls first, then tackle low-cost fabric fixes like draught-proofing and loft insulation. If you cannot change the building, focus on comfort where you sit and sleep: warm clothing, throws, heated throws or electric blankets use far less power than space heating.

If you plan a boiler replacement, consider low-temperature design. Larger radiators, balanced circuits and a reduced flow temperature help condensing boilers and heat pumps perform well, letting control strategies do more with less.