Dehumidifier vs Air Conditioner: Which Do You Need?
Both machines pull moisture out of the air, which is why people confuse them. One is built to dry a room, the other to cool it. In a UK home the right choice depends on whether your problem is damp or heat.
The short answer
Buy a dehumidifier if your problem is condensation, damp, mould or slow-drying washing. Buy an air conditioner if your problem is a bedroom that is too hot to sleep in. An air conditioner dries the air only as a side effect of cooling it, and only while it is cooling.
Dehumidifier vs air conditioner at a glance
The two machines share a compressor and a cold coil, but what they do with the heat is different.
| Dehumidifier | Portable air conditioner | |
|---|---|---|
| Main job | Removes moisture | Cools the room |
| Effect on temperature | Warms the room slightly | Lowers it |
| Needs a window hose | No | Yes, to vent hot air outside |
| Typical power | About 150-350 W | About 800-1,200 W |
| Useful season in the UK | Autumn to spring | A few hot weeks in summer |
| Dries laundry | Yes, most have a laundry mode | Poorly |
How each one works
A compressor dehumidifier draws room air over a cold coil. Water condenses and drips into a tank. The air is then passed over the warm side of the system and returned to the room dry and a degree or two warmer. An air conditioner does the same first step, then sends the heat outside through a hose or an outdoor unit. The room gets colder, and some moisture is removed along the way. When the room reaches the set temperature the compressor stops, and so does the drying.
Running cost
A 12L or 20L dehumidifier draws roughly 150 to 350 watts. A portable air conditioner draws around 1,000 watts. At a typical unit rate of about 25p/kWh, that is roughly 4 to 9p an hour against about 25p an hour. For keeping a house dry through a British winter, a dehumidifier is far cheaper. See our guide to dehumidifier running costs.
What about the dry mode on an air conditioner?
Most air conditioners have a dry mode. It runs the fan slowly so more water condenses on the coil. It helps on a muggy summer day. It is a poor substitute in winter: a portable unit still vents air outside through an open window gap, and it is not designed to run in a cool room.
Why a dehumidifier feels warmer
People are often surprised that a dehumidifier blows out warm air. Nothing is wrong: the heat taken from the water vapour, plus the heat of the motor, goes back into the room. In winter that is a small bonus, since dry air is also easier to heat. In a July heatwave it is the reason a dehumidifier is the wrong tool. If the room is hot, you need to move heat outside, and only an air conditioner does that.
Condensation in summer and winter
UK homes mostly suffer from damp between October and April, when warm indoor air meets cold windows and walls. That is exactly when an air conditioner sits unused. A dehumidifier holds the house at 50 to 55% relative humidity through those months, which is the range that discourages mould and dust mites. In a humid summer week, a dehumidifier can still help washing dry and stop a basement room smelling musty, as long as heat is not the main complaint.
Space, noise and installation
A dehumidifier needs a socket and a few centimetres of clearance. A portable air conditioner needs a window for its exhaust hose, usually with a sealing kit, and it is noticeably louder than a home dehumidifier, which runs at 35 to 50 dB. If the unit will run while you sleep, that gap matters as much as the bill.
Which should you buy?
Water on the windows, black spots in corners, a musty wardrobe, washing that takes two days: you need a dehumidifier. Our best dehumidifiers ranking is the place to start. A south-facing loft room at 30°C in July: you need an air conditioner, and a dehumidifier will make it feel worse because it adds a little heat. Hot and sticky in summer, damp in winter: many households end up with both, used in different seasons.
Meaco MeacoDry Arete Two 20L
20 litres/day · 4.4/5
Pro Breeze 20L OmniDry WiFi Dehumidifier
20 litres/day · 4.5/5
Meaco MeacoDry Arete One 12L
12 litres/day · 4.6/5
Ready to compare models? See our best dehumidifier uk comparison →
Frequently asked questions
Does an air conditioner work as a dehumidifier?
Partly. It removes some moisture while it is cooling, and more in dry mode. It stops drying when the room reaches the set temperature, and it is not suited to a cool, damp house in winter.
Is a dehumidifier cheaper to run than an air conditioner?
Yes. A home dehumidifier draws roughly 150 to 350 watts against around 1,000 watts for a portable air conditioner.
Does a dehumidifier cool a room?
No. It returns air slightly warmer than it took in. Drier air can feel more comfortable, but the temperature does not drop.
Should I use a dehumidifier or air conditioner for mould?
A dehumidifier. Mould grows where humidity stays high, which in the UK is mostly in the colder months, when an air conditioner is of no use.