How does a dehumidifier work?
Does your home suffer from signs of damp or condensation? Find out whether a dehumidifier will help solve the problem, how dehumidifiers work and how to make the most of your dehumidifier.
Dehumidifiers are designed to keep a room’s humidity levels in check, so the air is more comfortable and you notice fewer physical signs of damp air – such as mould on walls or condensation on your windows.
The best dehumidifiers are easy to use, won't cost you much to run and do a fantastic job of pulling water from the air whether working at room temperature or in colder conditions. The worst, on the other hand, will take much longer to do the same job.
How do dehumidifiers work?
Dehumidifiers draw excess moisture from the air, helping to combat condensation, prevent mould growth and reduce damp on walls.
There are two main types of dehumidifier to choose from – refrigerant (also known as compressor) and desiccant. They work in different ways and, as a result, are better suited to different environments.
Refrigerant (or compressor) dehumidifiers
As a general rule, if you know you'll always be using your dehumidifier in a heated room, go for a refrigerant. If you're going to be using it in an unheated room, or in a range of conditions, go with a desiccant.
That said, a couple of rare refrigerants work ok in colder temperatures too. These ones won't necessarily work terrifically in warmer temperatures of over, say, 26 degrees. But you might not be too fussed about that, British weather being what it is. How the defrost function has been set up also comes into play here. If a dehumidifier can spend less time defrosting, it can spend more time collecting water.
When should I use a dehumidifier?
Here are some signs that you need a dehumidifier:
- Your home has been flooded - or you notice water stains and think it may have been flooded before you moved in. First you'll need to fix the water damage, or get a professional to do so.
- The wood in your home is soft to the touch - which means it's rotting. Windowsills are particularly vulnerable.
- Your windows often have condensation.
- You notice mould and mildew. Check for little dark spots on your walls and ceilings, and the areas around your toilet and shower.
- Your home has an unpleasant musty smell.
You can use a dehumidifier across the year, in winter or in summer, if the humidity level is high. In summer, for example, you might want to use one if the air inside your house is humid and sticky, and opening a window just seems to let more hot air into your house.
Can a dehumidifier stop damp and mould?
You can use a dehumidifier when you notice signs of damp, such as condensation on your windows. But taking these simple steps could help nip it in the bud before it gets to the dehumidifier stage.
- Use an extractor fan or open a window when taking a bath or shower.
- Wipe down wet walls and floors in your bathroom after use.
- Seal cracks in your walls with a caulk or sealant.
- Place wet clothes to dry next to an open window. If possible, dry your clothes outside.
- When cooking on a hob, use the extractor fan hood.
If you’re having more persistent problems with damp, these tips may help. If not, you may need to call in a professional.
- Check gutters aren’t clogged and downspouts direct rainwater away from your home.
- Make sure your tumble dryer is properly vented to the outside.
- Check for any leaking pipes or appliances.
- A damp-proofing course may be needed for tackling structural rising damp.
Our tips on using your dehumidifier
- Vacuum before using your dehumidifier, so that it doesn't spread dust around the room or clog up the dust filter. This is particularly important if you suffer from allergies.
- You'd probably rather your dehumidifier was tucked out of sight. But you should position it away from walls, furniture and curtains so that air can circulate around it, and it can remove more moisture from the air.
- Keep doors and windows closed when the dehumidifier is running. If windows are open, your dehumidifier will be working harder to try to dehumidify a greater area.
- Empty the water tank after every use, if you can, and definitely before packing it away for storage.
- Use a cloth to wipe down the tank, so that you don't get mould or mildew from water that's been left stagnant.
- Vacuum the air filter on a regular basis to stop it getting blocked; manufacturers tell us that this is a very common reason for dehumidifiers not working properly.
- You can often wash your filter if it's very dirty. But check the manufacturer’s instructions first, as overzealous or inappropriate cleaning might damage your appliance and invalidate any warranty.
- Aim for the room’s humidity level to be between 50% and 60%. If you're buying a dehumidifier for a room containing valuable possessions, though, such as a guitar collection, seek specialist advice as to the humidity level you need.
How does continuous drainage work?
Dehumidifiers contain a water tank, which collects the water that is extracted from the air. You'll need to empty this regularly, ideally daily, to prevent the dehumidifier turning itself off once the tank is full.
Many dehumidifiers can be set up for continuous drainage. This involves attaching a hose (often not provided) to the dehumidifier and running the hose to a floor level drain, if you have access to one.
As this works through gravity, the dehumidifier will need to be raised a bit above the floor.
Choosing the best dehumidifier
Our test results of more than 45 dehumidifiers show that some are much quicker at pulling water from the air and more energy efficient, too, so they will make less of an impact on your energy bills.
If it's for a large room, you'll need a dehumidifier with a high claimed capacity, such as the . If it's for a smaller area, you can go for a model with a smaller claimed capacity such as the Click the links to see how these models performed when we put them through our tests.