Last Updated on October 24, 2026 by Umar Farooq
When to turn heating on to stop damp: as soon as the house starts to feel cold in the morning, and at the latest on the first day your windows are wet, rather than waiting for a calendar date. Condensation is the early warning, and by the time you can see mould you are already late.
No council page I opened gives a date, and I would be suspicious of any that did. What follows is three signs I would act on, a low, steady pattern for a damp-prone house, and the reason an early start costs less than the clean-up.
Why autumn is the month damp gets a head start
Condensation forms when damp air meets a surface colder than its dew point. I explain the mechanism in condensation on windows, so here is only the autumn part.
In early autumn the house is still carrying summer’s habits. Windows are shut against the first chilly nights, laundry has started moving indoors, and cooking and showering add moisture as usual. Outside, the nights are getting colder faster than the walls of your house are being warmed by anything. Glass, external walls and the corners behind wardrobes are the first surfaces to fall below the dew point, and with no heating yet they have nothing pushing them back up.
That is my reading of the physics, not a measurement from your home, but it matches the council advice below: Basingstoke and Deane says condensation forms when moist air is cooled by contact with cold surfaces, and that it often shows first as pinpoint black spots on the side surface of external walls.
When to turn heating on to stop damp: three signs to act on
Pick whichever arrives first.
- The first morning with wet windows. If glass is running with water when you get up, surfaces are already below the dew point. This is the most reliable sign because it is your own house telling you, not a forecast.
- The house drifting below about 18°C. Basingstoke council gives 18°C as the recommended room temperature, and 21°C for older people, children under five or anyone with a health condition. It does not frame that figure as a damp trigger, so treat the use as mine: a room that sits well under 18°C is cold enough that its walls will be colder still.
- The first run of cold nights. This one is a rule of thumb, not a sourced threshold: when the forecast turns cold for several nights in a row, switch on before the cold arrives instead of after. I have no outdoor temperature I can back with a source, so I am not going to invent one.
Notice what is missing: the date. Heating for damp follows the weather and the windows, which is why the same street can need heat three weeks apart.
Why starting early is cheaper than the mould clean-up
I am not going to put a pound figure on this. Heating costs depend on your insulation, your boiler or heat pump, your tariff and the winter, and none of the pages I opened gives a number I could trace.
The qualitative argument is straightforward. Early, gentle heat costs a small amount of fuel on days when you might otherwise have gone without. Late heat costs the fuel anyway, plus the wiping, the stain-blocking paint, the damp-smelling wardrobe and the clothes that have to be thrown out. Surface mould is far easier to prevent than to remove, and if you are already seeing it, the fix still starts with drying the surface and removing the source of the water.
Whether low heat all day costs more than a timer is a different argument, and the sources disagree. I cover it, with the trade-off, in low constant heating condensation. The timing question here is simply: do not let the house get cold in the first place.
A low, steady pattern for a damp-prone house
This is the routine I would use once the heating is on. Each point comes from a council page I opened, except where I say it is my own.
- Heat every room a little, not one room a lot. Epping Forest District Council says it is better to heat the whole home to a lower temperature than one room to a higher one. Unheated bedrooms are where moist air from the warm rooms finds cold walls.
- Keep low background heat on. Epping Forest advises low background heating on all day, even when nobody is at home. Basingstoke says low-level background heating should be continuous and that short bursts of heat may not raise surface temperatures enough.
- If you use a timer, start early. Swindon council suggests the heating comes on about an hour before everyone gets out of bed, and says that in very cold weather you can leave it on through the day and turn it down a few degrees when out.
- Ventilate rather than seal up. Basingstoke says keeping windows and vents closed to hold in heat will not reduce condensation, and suggests a few windows open a little throughout the home rather than one wide open. Epping Forest suggests a trickle vent or a window ajar while a room is in use.
- Pick a sensible target. Aim near the 18°C figure above, not a tropical living room. The point is to keep the walls warm, not to make the air as hot as possible.
Keep the laundry off the radiators
Basingstoke says plainly not to dry clothes directly on radiators. Wet washing releases its water into the room just as the heating is trying to keep walls warm, so the two cancel out. Swindon’s advice is to dry outside where you can, otherwise in the bathroom with the door closed and a window open or the extractor on. If you use a heated airer, do heated airers cause damp covers what to expect.
What the heating cannot do for you
Heat keeps surfaces warm, but it does not remove water. A home producing a lot of moisture, with weak ventilation, can still run damp with the boiler on. That is the point to measure rather than guess: ideal home humidity level in winter explains which readings to aim for. If the walls are warm and the windows are still wet, ventilation and moisture control are the next fix, not a higher thermostat.
Heat on at the first wet window, and keep it low and steady
My opinion, plainly: the answer to when to turn heating on to stop damp is the first morning your windows are wet, or earlier if a cold week is coming. Run low heat in every room, ventilate a little, and keep washing off the radiators. You will spend a bit of fuel in October that you could have saved, and you will not be scrubbing black spots out of a corner in January.
FAQ
Is there an official date to turn the heating on to stop damp?
No. None of the council pages I opened give a date, and damp follows the weather and the condition of your home rather than the calendar. Use the signs above: wet windows, a cold house, or a cold spell on the way.
What temperature should I keep my house to stop damp?
Basingstoke council gives 18°C as the recommended room temperature, and 21°C for older people, children under five or anyone with a health condition. That is a general comfort and health figure, so I would use it as a sensible target rather than a guaranteed damp limit.
Should I heat rooms nobody uses?
A little, yes. Epping Forest District Council says it is better to heat the whole home to a lower temperature than one room to a higher one. A cold, unused room is where moist air from the rest of the house tends to condense on cold walls.
Is it too late to turn the heating on once I see mould?
Not too late to help, but heat alone will not fix it. Clean the affected surface, find and stop the source of the moisture, and keep the room warm and ventilated so it does not come back.
Is it better to heat in short bursts or keep it low all day?
Basingstoke says short bursts may not raise surface temperatures enough, so low and steady is the safer pattern for a damp house. Whether it costs more on your bill is covered in the low constant heating guide linked above.
