Heating on low all day or just on demand: could your family blow £150 as prices rise this autumn?

Cold snaps are coming and bills are edging up, leaving many of us torn between comfort, condensation and cash.

MoneySavingExpert founder Martin Lewis has revisited the question that returns every year: keep the heating on low all day, or run it in timed bursts? His guidance points one way for most homes, and flags a clear exception for properties that battle damp.

What Martin Lewis actually advises

For typical gas‑heated homes, the advice is simple: do not keep the heating on low all day. Heat the house only when you need it and let your thermostat and timer manage the temperature. That approach reduces the hours your system runs, trims wasted heat loss, and gives you warmth at the times you value it.

For most households, run the heating when you need it, use a timer, and let the thermostat control comfort.

Lewis also points people towards timers. A well‑set programmer preheats rooms before you wake or get home, then switches off when you do not need it. Your thermostat stops overshoot by cutting the boiler once the set temperature is reached.

Why ‘on when needed’ usually wins

Heat loss rises the longer your home sits warm against cold outdoor air. Keeping a continuous background temperature extends that window of loss across the day. Timed heating shortens it. You add heat when occupied, then let the house cool a little when you are asleep or out. Thermostatic radiator valves (TRVs) can lower temperatures in spare rooms so you do not pay to heat empty space.

The condensation exception

Some homes are different. Where walls are cold and insulation is weak, switching the heating off can load surfaces with moisture. Wet fabric conducts heat away faster and can encourage mould. In these cases, a gentler, more constant background heat may help keep surfaces dry and stabilise humidity, especially if paired with ventilation or a dehumidifier. That can make the house feel warmer at lower settings and reduce the energy needed to reheat from cold.

Homes that suffer damp or recurring condensation may spend less overall by keeping a steady, low heat and managing moisture.

If you suspect this applies, test it. Track humidity with a simple meter, note how often windows mist, and compare your daily gas use under both strategies over a fortnight. Choose the one that gives you dry walls, good air, and the lowest kWh for the comfort you want.

What real households are doing

When the question landed on Lewis’s forum, readers shared approaches that reflect the two camps. One poster lets the thermostat work between 15°C and 20°C when at home, then drops it to 10°C when out. Another, in a well‑insulated new build, uses short timed boosts to 20°C from 6am to 7am and 5pm to 8pm, switching off completely in summer.

• “Set and forget” with a room stat: 15–20°C when in, 10°C frost‑protect when away.
• Timed bursts: 20°C for an hour before getting up, and early evening top‑ups.
• Insulated homes: shorter, sharper heat‑ups hold temperature for longer.

How to set up your system for less waste

A few small tweaks can save pounds without chilling the house.

• Use your programmer: schedule heating for wake‑up and return‑home times. Add a short preheat so rooms are ready on time.
• Pick a sensible setpoint: many households feel fine at 18–20°C in living spaces. Keep rarely used rooms cooler with TRVs.
• Avoid big swings: huge temperature jumps invite long boiler runs. Nudge setpoints by one degree at a time.
• Lower boiler flow temperature: many condensing boilers run more efficiently around 55–60°C flow. If radiators feel too cool, increase a little.
• Seal draughts: close trickle vents only when cooking or showering will be ventilated; fit letterbox brushes and door seals.
• Control moisture: pan lids on, extractor fans on, shorter showers, and dry clothes outside or with a dehumidifier where possible.
• Zone your home: keep bedrooms cooler than living rooms; shut doors to hold heat where you need it.
• Smart controls help: occupancy features can trim heat when you step out and resume before you return.

Small temperature changes matter: dropping the thermostat by 1°C can cut gas use by roughly 5–10% in many homes.

A quick cost sketch you can adapt

Numbers will vary by house, weather and tariff, so treat this as a guide. Read your meter to get real‑world figures for your home.

These figures assume a part‑load boiler output averaging around 7 kW while firing. Your duty cycle will differ. The key is to compare patterns using your own meter readings. If timed heating gets you the same comfort for fewer kWh, it is the cheaper path. If a steady low setting dries out a damp home and reduces reheating losses, that may win despite running longer.

What to check before you pick a strategy

• Insulation level: good loft and cavity wall insulation favour timed heating. Poorly insulated, damp‑prone walls may need steadier warmth.
• Humidity: aim for 40–60% relative humidity. Persistent condensation on windows suggests you should address moisture and ventilation first.
• Health needs: very young, older, or unwell people often need warmer, steadier temperatures. Keep living areas at least 18°C for safety.
• Boiler type: condensing gas boilers like lower flow temperatures and longer, gentler cycles; non‑condensing models are less sensitive.
• Heat pumps: different rules. They generally run best at low flow temperatures, more continuously, with small setpoint changes.

Extra context as the price cap rises

Bills are forecast to climb as the price cap moves up, so the cheapest kWh is the one you do not use. Start with free or low‑cost wins: draught proofing, tighter schedules, lower flow temperature, and trimming setpoints by a degree. If you rent, tell your landlord promptly about damp, broken extractors or failed seals; better ventilation plus minor repairs can cut mould risk and save you money.

If you are struggling, check whether you qualify for support schemes or supplier‑run grants, and ask your energy firm about affordable repayment plans. A quick self‑audit helps too: note which rooms actually need to be warm, and heat those first. For many households, the Martin Lewis playbook holds: heat when you need it, automate with a timer, and keep moisture in check. For homes that fight damp, a steady, gentle baseline paired with good ventilation may deliver comfort at a lower overall cost than you expect.