Dehumidifier vs air conditioner

The same cycle, different jobs

In a dehumidifier, room air passes over the cold coil, where water condenses into the tank, then over the warm coil inside the same box. All the heat stays in the room, plus a little extra from the compressor motor. The air comes out drier and slightly warmer. That is ideal in a damp British winter or for drying washing.

In an air conditioner, the warm coil sits in the outdoor unit, or in the case of a portable unit, its heat is blown out of a window through an exhaust hose. Heat leaves the room, so the room cools. Water still condenses on the cold coil, and portable units either evaporate it into the exhaust air or collect it in a tank.

What happens to temperature and humidity

Run a dehumidifier in a closed room and humidity falls while temperature edges up by a degree or two. Run an air conditioner and temperature falls, with humidity usually falling too. On a humid summer day, the cooler, drier air from an air conditioner feels much more comfortable than air that is only drier.

Many portable air conditioners have a dry or dehumidify mode. It runs the compressor with a low fan to remove moisture without much cooling. It can be handy in spring or autumn, but it still needs the exhaust hose fitted in most designs, so check the manual.

Energy use and running hours

A home compressor dehumidifier typically draws a few hundred watts, and the humidistat switches it off once the target is reached. A portable air conditioner usually draws considerably more, often around a kilowatt on cooling, because it is moving heat out of the room. Check the rating plate of the exact model, then use our running-cost calculator with your own unit rate.

A dehumidifier is far cheaper to run for drying a damp room. An air conditioner only makes sense when you need cooling.

Which to buy

For condensation, damp walls, musty smells or drying laundry, buy a dehumidifier. It is cheaper to buy and run, needs no window hose and works through the colder months when damp is worst. For a bedroom that gets unbearably hot in summer, a portable air conditioner is the tool that actually cools. Some households own both and use each in its season.

Running hours differ too. A dehumidifier on a humidistat may cycle on and off through the day and run for only part of the time once the room has dried. An air conditioner in a heatwave tends to run for long stretches while the sun is on the windows. Closing curtains on sunny sides of the house and opening windows on cooler evenings both cut the hours an air conditioner needs.

• Winter condensation: dehumidifier
• Drying washing indoors: dehumidifier
• Hot loft bedroom in July: air conditioner
• Muggy spring days: either, or an air conditioner in dry mode

Compare the best dehumidifiers for UK homes →

Can a dehumidifier cool a room?

No. A dehumidifier makes a room feel a little fresher in muggy weather because drier air lets sweat evaporate, but the thermometer will read slightly higher, not lower. If you want both, a fan alongside a dehumidifier helps comfort without cooling the air itself. Our dehumidifier vs fan comparison covers using the two together for laundry.

If you only need help for a few hot weeks a year, consider whether a fan and closed curtains will do. If the damp months are the bigger problem, put the money into a good dehumidifier first. Our where to put a dehumidifier guide helps you get the most from it.

Frequently asked questions

Does an air conditioner remove humidity? Yes. Water condenses on its cold coil, so humidity usually falls while it cools. Portable units either evaporate the water out of the exhaust hose or collect it in a tank.

Can I use a portable air conditioner as a dehumidifier? Many have a dry mode, but most still need the window hose fitted and they are bulky and power hungry compared with a dedicated dehumidifier.

Why does my dehumidifier blow warm air? Because all the heat from its coils and compressor stays in the room. That is normal and part of why it works well in winter.