How to use a dehumidifier — where to put it, settings and how long to run it

Most dehumidifier complaints — “it’s not doing anything”, “it costs a fortune”, “the windows are still wet” — come down to how and where it’s used rather than the machine. Get these few things right and even a modest unit makes a big difference.

Where to put a dehumidifier

In the problem room. Put it where the condensation, mould or laundry is — usually a bedroom, the laundry room or the coldest room in the house.

20–30cm away from walls and furniture. Air needs to flow into the intake and out of the outlet. Don’t push it into a corner or behind a sofa, and keep curtains and drying clothes away from the vents.

On a hard, level floor. It’s more stable, vibrates less (so it’s quieter) and the float switch in the tank works properly.

Near the moisture, not the window itself. A spot a metre or two from the window, or near an outside wall where mould forms, works well. Right against a draughty window it partly dries outside air.

Centrally, if it’s for the whole home. A larger unit on the landing or in a hallway, with internal doors open, can serve several rooms — useful in flats and smaller houses.

Not in the bathroom. UK bathrooms rarely have suitable sockets, and portable dehumidifiers aren’t designed for wet zones. Place it just outside with the door open after a shower — see dehumidifiers for bathrooms.

Doors and windows: open or closed?

Situation	Windows	Door
Drying one room (bedroom, box room)	Closed	Closed
Drying washing	Closed	Closed
Serving the whole flat or house	Closed	Open, with the unit on the landing or hallway
After a shower (unit outside bathroom)	Closed	Bathroom door open

Ventilation and dehumidifying are separate jobs. Airing the house for 10–15 minutes in the morning is still worthwhile — just close the windows again before switching the dehumidifier on.

What humidity to set

Set the humidistat to around 50%. That’s comfortably inside the healthy 40–60% range and low enough to stop most condensation — see ideal humidity in a UK house. In a cold snap with stubborn window condensation, 45% can help. Going much lower wastes electricity.

How long to run a dehumidifier

There’s no single answer, but these are sensible starting points:

• Persistent damp or daily condensation: 12 hours or more a day for the first week or two, while walls and furnishings dry out. Then let the humidistat manage it.
• Bedroom condensation: in the evening and for an hour or two after you get up — or overnight on a quiet setting. See the best dehumidifier for a bedroom.
• Drying laundry: 4–8 hours, or one laundry-mode cycle. See drying clothes with a dehumidifier.
• After a shower: 30–60 minutes, until the bathroom is back below about 60%.
• Maintenance: once the house is dry, leave it on auto at 50% and it will run only when needed.

With a humidistat, “how long” mostly takes care of itself — the unit runs until the room reaches your target, then rests. That’s also what keeps running costs down.

Look after it

• Empty the tank daily in damp weather, or fit a drain hose on Amazon (opens in a new tab) (paid link) to the continuous drainage outlet where there’s a sink or drain nearby.
• Clean the filter every couple of weeks — a clogged filter cuts airflow and performance.
• Keep it upright. If a compressor model has been laid on its side, check the manual; many recommend standing it upright for a few hours before switching on.
• Don’t run it on a coiled extension lead, and keep the cable out of walkways.

Still not working?

If the tank stays empty or the humidity won’t come down, the usual culprits are a cold room, the humidity setting, open doors or windows, or a blocked filter — see dehumidifier not collecting water. And if the damp is a patch on one wall rather than condensation, read how to tell condensation from damp.