The essentials in 30 seconds
Indoor humidity is best kept below 60 %, ideally between 30 % and 50 %. If a hygrometer shows higher readings for days, you will see misted windows, mould in corners and a musty smell. A dehumidifier pulls water out of the air and helps with condensation, drying laundry, cellars and homes closed up for a while. Compressor models suit heated rooms; desiccant models work better in cold rooms such as garages or unheated spare rooms. Set the humidistat to about 50 % and keep ventilating every day.
- Measure first: a hygrometer costs very little.
- Choose the capacity for the room and the problem.
- A dehumidifier does not fix leaks, rain coming in or rising damp.
When a dehumidifier makes sense
| Situation | Does a dehumidifier help? | Also |
|---|---|---|
| Misted windows and mould in corners in winter | Yes | Ventilate and check for cold spots |
| Drying laundry indoors | Yes | Ventilate the room where it dries |
| Damp cellars, basements or storerooms | Yes, as support | Check for rising damp or leaks |
| Home closed up for weeks | Yes | Air it when you return |
| Patch that grows after rain | It is not the fix | Find where water is getting in |
| Tide mark low on the wall with salts | It is not the fix | Get rising damp diagnosed |
| Patch under a bathroom or pipe | No | Repair the leak |
Compressor or desiccant
| Type | How it works | Best for | Bear in mind |
|---|---|---|---|
| Compressor | Cools air over a coil so water condenses | Heated rooms, roughly 15 °C and above | Less effective in cold rooms; some noise |
| Desiccant | A material absorbs moisture and is dried by a heater | Cold rooms, garages, unheated spaces in winter | Usually uses more electricity; gives off some warmth |
| Moisture absorbers (no power) | Crystals collect water in a tub | Wardrobes and small spaces | Very limited capacity |
What capacity to choose
Capacity is shown in litres per day under test conditions, which are usually more favourable than a real home. As a guide:
- Wardrobes and small bathrooms: absorbers or small units.
- Bedrooms and living rooms with moderate condensation: mid-size units.
- Very damp homes, cellars or drying laundry: larger units with continuous drainage.
Also look at the tank size, continuous drainage through a hose, a humidistat so it stops at your chosen humidity, a laundry mode and the noise level if it will run in a bedroom.
How to use it well
-
01
Measure the humidity
Place a hygrometer away from windows and steam and note the readings for a few days.
-
02
Close the room
Keep doors and windows shut while it runs, so you dry the room, not the street.
-
03
Set the target
Set the humidistat to about 50 %. There is no need to go much lower.
-
04
Place it well
In the middle of the room or near the problem, with free space around the grilles.
-
05
Empty the tank
Or connect continuous drainage to a sink or drain.
-
06
Keep ventilating
Open the windows for a few minutes every day to renew the air.
Looking after your dehumidifier
- Clean the filter every few weeks with water or a vacuum.
- Wash the tank with soapy water to prevent smells and mould.
- Keep the grilles free of dust.
- Store it clean and dry when not in use.
What to do as well as using a dehumidifier
- Run the extractor fan in the bathroom and kitchen when showering and cooking.
- Cover pans and dry clothes outdoors when you can.
- Keep a steady temperature in winter: cold walls condense more.
- Improve insulation and windows if there are cold spots, while keeping the home ventilated.
- For persistent mould, read our guide to black mould on walls.
Dehumidifiers: frequently asked questions
What humidity should my home be?
Below 60 %, ideally between 30 % and 50 %. A humidistat setting of about 50 % works for most homes.
Compressor or desiccant?
Compressor for heated rooms; desiccant for cold rooms, garages and unheated spaces in winter.
Does a dehumidifier stop mould?
It helps by cutting condensation, but existing mould still needs cleaning, and leaks or rising damp need fixing.
Can I dry clothes with a dehumidifier?
Yes. Close the room, use the laundry mode if it has one and empty the tank often.
Where should I put it?
In the dampest room, away from walls and furniture, with the doors and windows closed while it runs.
Should it run all the time?
Let the humidistat decide: it switches off when the room reaches the humidity you set.
Sources
Official guidance on humidity, ventilation and damp, checked on 24 October 2026.
- US EPA · A brief guide to mold, moisture and your home ↗Keep indoor humidity below 60 %, ideally 30–50 %; use dehumidifiers when humidity is high.
- GOV.UK · Understanding and addressing the health risks of damp and mould in the home ↗Condensation, ventilation, extractor fans and everyday habits.
- WHO · Guidelines for indoor air quality: dampness and mould ↗Health effects of damp indoors.
Still fighting condensation?
Log the humidity for a week in each room before you buy: it tells you which type and size you need.