Key takeaways
- Dehumidifier capacity is measured in litres of water removed per day.
- Rough guide: 10 to 12 L/day for a small or average home, 16 to 20 L/day for a larger home or laundry drying, 20 to 25 L/day+ for serious damp or mould.
- Pick a compressor model for normal heated rooms and a desiccant model for cold spaces like garages.
- Rated extraction is measured in warm, humid lab conditions, so expect less in a cool UK home.
Dehumidifier sizing is easier than air conditioner sizing, but the litre figure on the box still confuses people. Here is what the capacity number means, what size suits your home, and why the advertised extraction is always higher than what you will actually see.
How dehumidifier capacity works
Capacity is the amount of water a dehumidifier can pull from the air in a day, measured in litres. A bigger number means it clears moisture faster and copes with damper rooms. Unlike an air conditioner, a slightly oversized dehumidifier is not a problem, because once the air reaches the target humidity the machine idles. The trade-offs of going bigger are price, size and weight rather than wasted energy.
What size dehumidifier do I need?
| Home or situation | Recommended capacity |
|---|---|
| 1 to 2 bedroom flat, mild damp | 10 to 12 L/day |
| 3 to 4 bedroom house, some damp or laundry | 16 to 20 L/day |
| Large house, persistent damp or mould | 20 to 25 L/day or more |
| Cold garage, basement or unheated room | Desiccant model, 8 to 12 L/day |
Compressor or desiccant?
The other choice is the type. A compressor dehumidifier is the efficient pick for normal heated rooms and suits most homes. A desiccant model keeps working in the cold, so it is the better choice for a garage, basement or unheated room, and it is lighter and quieter, though it draws more power. If the space you are drying is warm, go compressor; if it is cold, go desiccant.
Why the advertised litres are optimistic
Manufacturers measure extraction in warm, humid lab conditions, often around 30°C and 80 percent humidity. A typical UK home is cooler and less humid, so you will see noticeably less than the headline figure in everyday use. That is the main reason to pick a model a step above the bare minimum for your home. When you are ready to choose, see our pick of the best dehumidifiers.
Common questions
What size dehumidifier do I need?
For a small or average UK home, a 10 to 12 litres-per-day model is enough. Choose 16 to 20 litres for a larger home or regular indoor laundry drying, and 20 to 25 litres or more for serious damp or mould.
Is a bigger dehumidifier always better?
Not always, but oversizing matters far less than with air conditioners. A higher-capacity model simply reaches the target humidity faster and then idles, so the main downsides are cost, size and weight.
Compressor or desiccant dehumidifier?
Compressor models are the most efficient in normal heated rooms and suit most homes. Desiccant models work better in cold spaces such as garages and unheated rooms, and are lighter, but they use more electricity.
Why is the advertised extraction higher than what I get?
Rated litres-per-day figures are measured in warm, humid lab conditions, usually around 30°C and 80 percent humidity. A normal, cooler UK home is less humid, so real-world extraction is lower, which is one reason to choose a slightly larger model than the bare minimum.