Dehumidifier buying guide
By Kyle Marshall Rance. Updated .
Damp, condensation and mould are the UK's winter problem. A good dehumidifier fixes the cause instead of wiping the windows every morning. This guide covers how to size one honestly, which type suits a cold British house, what laundry mode is worth, and what one costs to run.
Compressor or desiccant?
Compressor dehumidifiers work like a small fridge: air passes over a cold coil, water condenses and drips into the tank. They are the most energy efficient type in a normally heated room, typically drawing 150 to 250 W. Their weakness is cold: below about 15°C the coil struggles and extraction drops sharply.
Desiccant dehumidifiers pull moisture out with an absorbent wheel that a small heater dries out again. They keep working in cold rooms, garages and conservatories, are usually quieter, and give off a little warmth. The trade-off is power: 300 to 650 W is normal.
Rule of thumb: heated living space, choose a compressor unit. Unheated rooms or a house kept below about 15°C, choose desiccant.
Sizing: what "litres per day" really means
Extraction figures are measured at 30°C and 80% humidity, conditions a UK home in winter never sees. In a typical 18 to 20°C room a compressor unit removes roughly a third to a half of its headline figure. So size up, not down.
- Flat or small house, mild condensation: 10 to 12 L/day.
- 2 to 3 bed home, or drying laundry indoors: 12 to 20 L/day.
- 3 to 4 bed home, persistent damp or visible mould: 20 to 25 L/day.
- Large homes, cellars, severe damp: 25 L/day and up.
We only track electric units rated 6 L/day or more. Mini units rated in millilitres and non-electric moisture traps can help a wardrobe, but they will not dry a room.
Laundry mode
Drying clothes indoors puts litres of water into the air. Laundry mode runs the fan and compressor flat out regardless of the humidity reading, and many owners use it instead of a tumble dryer. It is the single most useful feature for UK households without outside drying space.
Features worth paying for
- Humidistat: set a target (around 50 to 60%) and the unit switches itself on and off.
- Continuous drain: a hose outlet means you never empty the tank, ideal for cellars and utility rooms.
- Tank size: 2 L or more saves emptying it twice a day.
- Noise: under 40 dB is fine for a bedroom; many units have a quieter night mode.
Running cost
At around 25p per kWh, a 200 W compressor unit running 8 hours a day costs about 40p a day. A 500 W desiccant unit over the same hours is about £1. A humidistat cuts this a lot, because the unit stops once the room is dry.
Can a 3-in-1 portable air conditioner do the job?
Many portable air conditioners list a dehumidify mode. It does remove moisture, but these units are built for summer cooling: they need a hose out of a window, they are heavy and loud, and they are not designed for cold rooms. For winter damp and laundry, a dedicated dehumidifier is the right tool. Looking for cooling instead? See our portable air conditioner guide.
How we put this guide together
Extraction, power and noise figures come from manufacturers' published specifications and the UK retailer listings we track. Our real-world extraction estimate (a third to a half of the headline figure in an 18 to 20°C room) reflects the gap between the 30°C and 80% humidity test conditions and a typical UK home in winter. Running costs assume about 25p per kWh, a round figure close to typical UK unit rates, so scale them to your own tariff. We have not lab-tested every model. Written by Kyle Marshall Rance. Spotted something out of date? Email hello@aircondrop.co.uk.
Quick answers
What size dehumidifier do I need?
For a flat or small house with mild condensation, 10 to 12 litres per day. For a 2 to 3 bed home or drying laundry indoors, 12 to 20 L/day. For a 3 to 4 bed home with persistent damp or mould, 20 to 25 L/day. Headline figures are measured at 30°C and 80% humidity, so a unit removes much less in a normal UK room. Size up, not down.
Compressor or desiccant dehumidifier for a cold house?
Choose a desiccant dehumidifier for unheated rooms, garages, conservatories or a house kept below about 15°C, because compressor units lose most of their extraction in the cold. In a normally heated home a compressor dehumidifier is the more energy-efficient choice.
How much does a dehumidifier cost to run in the UK?
At around 25p per kWh, a 200 W compressor dehumidifier running 8 hours a day costs about 40p a day. A 500 W desiccant unit over the same hours costs about £1. A humidistat reduces this because the unit switches off once the room reaches its target humidity.
Can I dry clothes with a dehumidifier?
Yes. Laundry mode runs the dehumidifier flat out regardless of the humidity reading, and many UK households use it instead of a tumble dryer. For regular indoor drying, pick a unit rated 12 L/day or more.
What humidity should I set a dehumidifier to?
Around 50 to 60% relative humidity. That is dry enough to stop condensation and mould, and a humidistat will switch the unit on and off to hold it there.
Will a dehumidifier get rid of mould?
It removes the damp that mould needs to grow, so it stops new mould forming and helps existing patches dry out. You still need to clean off existing mould, and persistent damp from a leak or rising damp needs the cause fixed.