From about the middle of September, washing stops drying outside reliably and starts drying inside instead. For a lot of British households that's the point at which condensation appears on bedroom windows, and the two things are connected more directly than most people realise.
A load of laundry doesn't lose its water to some abstract place. It puts it into the air in your house — around two litres per load — and that water has to leave the building or it will condense somewhere.
The Short Answer
Dry in one room, with the door shut and a window open a crack. That's the whole method. Contain the moisture, then give it a route directly outside rather than letting it circulate through the house.
Specifically:
- One room only — ideally not a bedroom, and ideally the coolest room you can spare
- Door closed, so the moist air doesn't migrate to cold external walls elsewhere
- Window on the latch, or an extractor running, so the moisture actually leaves
- Spin at the highest speed the fabric allows — this removes water mechanically before it ever becomes airborne
Don't dry on radiators. It's the worst option on every measure: it puts moisture into the room fastest, it blocks the heat output you're paying for, and it concentrates humidity in the room you're most likely to be sitting in.
A dehumidifier in the same room is the proper fix if you're doing this all winter. It collects the water rather than moving it around, and it costs a fraction of what a tumble dryer does.
What Actually Matters
Three things, and the first one is the one people find surprising.
The quantity of water involved. A washing machine spinning at 1400rpm leaves roughly half the load's weight in water. An 8kg load therefore holds something in the region of four kilograms of water when it comes out, and while some of that drips away, a substantial part — commonly around two litres — evaporates into your house.
Two litres of water, released into the air of a normal home, is a meaningful amount. Do it three times a week and you're adding six litres a week to an indoor environment that in winter has very little natural ventilation.
Where it condenses. Warm air holds more water than cold air. As moist air moves through the house and reaches a cold surface — a single-glazed window, an uninsulated external wall, the cold corner behind a wardrobe — it cools, can no longer hold the moisture, and deposits it. That's condensation, and repeated condensation on the same surface is what grows mould.
Spin speed, which is free. Every litre the washing machine removes mechanically is a litre that never enters your air. Spinning at 1400 rather than 1000 makes a genuine difference to how much moisture ends up in the room, and it costs nothing.
Detailed Analysis
Why the door-shut-window-open method works
It seems contradictory — you're heating the house and opening a window — but the logic holds up.
Moisture always moves from where there's more of it to where there's less. Left to circulate, humid air from your drying laundry will find every cold surface in the house and condense on the coldest ones. Those are usually in bedrooms, behind furniture, and in corners where air doesn't move.
Shutting the door confines the humidity to one room. Opening a window in that room gives it somewhere to go that isn't your bedroom wall. The heat loss from a window on the latch in one room is small; the cost of dealing with mould on a bedroom wall is not.
Choose the room deliberately. A spare room, a utility room, a bathroom with an extractor, or a hallway all work. Avoid bedrooms — you don't want to sleep in the humidity — and avoid rooms with a lot of soft furnishings that will absorb it.
Why radiators are the worst option
This one's worth being firm about, because it's what most people do.
Draping wet washing over a radiator evaporates the water as fast as possible, straight into the room. That's the opposite of what you want when the aim is to limit humidity.
It also blocks the radiator. A radiator works partly by radiating heat and partly by convecting warm air upwards, and covering it with wet fabric stops both. Your heating system runs longer to reach the same room temperature, which costs money.
And it concentrates the humidity in whichever room the radiator is in — usually a living room or a bedroom, which are exactly the rooms where you least want it.
If you have no alternative, an airer positioned near a radiator rather than on it is considerably better. The heat still helps, the radiator still works, and the drying is slower and less concentrated.
Dehumidifiers, and what they actually do
A dehumidifier removes water from the air and collects it in a tank. Unlike ventilation, it doesn't need you to open anything, and unlike a tumble dryer, it doesn't cost much to run.
Typical domestic models draw somewhere between 150W and 500W. At the Ofgem capped rate of 26.32p per kWh for October to December 2026 — substitute your own rate — running a 300W unit for six hours costs around 47p. A vented tumble dryer load costs around £1.05 at the same rate.
The other benefit is that you can see the water. A dehumidifier running in a room with drying washing will fill its tank, and looking at a litre and a half of collected water is a fairly persuasive demonstration of what would otherwise have gone onto your windows.
Most have a laundry or continuous mode that runs the fan harder and skips the humidity target. That's the setting to use for drying washing.
Two types exist. Compressor models are more efficient in warm rooms; desiccant models work better in cold ones, which matters if you're drying in an unheated utility room or a cold spare bedroom. For a British house in winter, a desiccant unit is often the better choice despite being slightly less efficient on paper.
Getting the water out before it becomes airborne
The cheapest intervention available and the one most often skipped.
Spin speed determines residual moisture. Roughly speaking, a 1000rpm spin leaves cottons at around 60% residual moisture; 1400rpm leaves around 50%; 1600rpm a little less. Those differences translate directly into how much water enters your room.
For towels, bedding and everyday cottons, spin at the highest speed the machine offers. The creasing penalty is real but modest, and it's a smaller problem than condensation.
An extra spin cycle on a load that's coming out for indoor drying is worth the few minutes and the negligible electricity. It's the difference between two litres going into your air and rather less.
Real-World Considerations
Flats are the hardest case. Often no outdoor space, frequently no tumble dryer, sometimes restrictions on what can be installed. The dehumidifier answer is particularly strong here, because it needs nothing but a socket.
Modern homes can be worse than older ones for this, which is counterintuitive. A well-sealed, well-insulated house has very little accidental ventilation, so moisture that goes in tends to stay in. Older draughty houses lose humidity through gaps constantly. If you've had a house made more airtight — new windows, insulation, draught-proofing — and condensation has appeared since, that's usually why.
Trickle vents on modern windows exist for exactly this and are frequently taped shut or left closed because of draughts. Opening them in the drying room is a small, free improvement.
Extractor fans in bathrooms are worth using deliberately. Drying washing in the bathroom with the extractor running gives you contained humidity and mechanical extraction — arguably the best arrangement most homes already have.
Watch for the early signs rather than waiting for mould. Condensation on the inside of windows in the morning, a musty smell in a particular room, or a cold spot on a wall that feels damp to the touch are all warnings that the moisture isn't leaving.
And if clothes take more than about a day to dry indoors, something is wrong with the arrangement — usually inadequate airflow around the load. Spacing items out on the airer matters more than people think, and an overloaded airer with everything touching will take three days and put moisture into the house for all of them.
Common Mistakes Buyers Make
- Drying on radiators. Fastest possible release of moisture into the room you're sitting in, plus a heating system working harder.
- Drying in a bedroom with the door open. The humidity migrates through the house and finds the coldest wall.
- Keeping windows shut to save heat. The moisture has to leave somehow. A window on the latch in one room costs very little.
- Spinning at low speed to protect clothes. Every litre left in the load ends up in your air.
- Overloading the airer. Items touching each other dry slowly and extend the period you're adding moisture.
- Buying a compressor dehumidifier for a cold room. Desiccant models perform better below about 15°C.
- Taping trickle vents shut. They're the background ventilation the house was designed around.
- Treating mould as a cleaning problem. Wiping it off without changing the moisture source means it returns.
Alternatives Worth Considering
A heated airer is a genuinely useful middle option. They draw very little — commonly 100-300W — and speed up drying substantially compared with a plain airer. Used with a cover, they become something close to a slow, cheap tumble dryer. They still release the moisture into the room, so the ventilation advice still applies.
A heat pump tumble dryer is the answer if you can accommodate one. Unlike a vented dryer it needs no hole in the wall, and unlike a condenser it doesn't warm and humidify the room significantly. Running costs are roughly a third of a vented machine's.
For households with a bathroom extractor, using that room deliberately for drying is the cheapest version of the correct method. Contained, mechanically ventilated, and it costs pennies.
And where the problem is really that too much washing is being done at once, spreading loads across the week rather than doing four on a Sunday keeps the peak humidity down. Two litres a day is manageable; eight litres in an afternoon is not.
Frequently Asked Questions
Does drying clothes indoors cause damp?
It adds around two litres of water to the air per load. Whether that becomes damp depends entirely on whether the moisture is ventilated out or allowed to condense on cold surfaces.
Should you open a window when drying clothes inside?
Yes — in the drying room, with the door shut. That gives the moisture a route outside rather than through the rest of the house.
Is it bad to dry clothes on radiators?
It's the worst option. It releases moisture fastest into a living space and stops the radiator heating the room properly.
Is a dehumidifier cheaper than a tumble dryer?
Considerably. A dehumidifier running for six hours costs well under 50p at current rates against around £1 for a vented dryer load.
Which dehumidifier is best for a cold room?
A desiccant model. Compressor dehumidifiers lose efficiency below about 15°C, which covers a lot of British utility rooms in winter.
How long should washing take to dry indoors?
Under a day with reasonable airflow and spacing. Longer than that suggests the load is too tightly packed or the room isn't ventilated.
Final Thoughts
The instinct in winter is to keep everything shut and let the heating deal with it, and that's precisely the combination that produces condensation on bedroom walls in February.
Contain the washing in one room, give that room a way to breathe, and spin the load hard before it comes out of the machine. Those three habits handle most of it for nothing.
If you're drying indoors all winter every winter, a dehumidifier earns its money quickly — both in what it saves against a tumble dryer and in what it prevents on the walls.
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