Why do I need a dehumidifier?
Dark patches on your walls, condensation on your windows and patches of black mould or mildew are all signs your house is suffering from damp - this happens when the humidity level regularly goes above 60%.
A lack of ventilation, leaky pipes or poor insulation can cause damp, but daily life does have an impact, too - for instance, cooking, showers and drying washing indoors all add excess moisture to the air. And some houses, built before the advent of central heating and decent extractor fans, just aren’t up to coping with modern life.
So, how does that affect you? Living in a mouldy and damp home can cause serious health issues, particularly for allergy and asthma sufferers, which include an increased risk of respiratory illness and infections. Additionally, damp can make your home look unattractive and give it a musty smell, with the excess moisture causing damage to your walls, carpet, ceiling and furniture.
That’s where a dehumidifier can help. By removing excess moisture from the air, a dehumidifier helps to keep humidity levels under control, reduce condensation and create a drier, more comfortable home. It can also help prevent the conditions that allow mould and mildew to thrive, while making it easier to dry clothes indoors.
Related: The best moth repellents for protecting your cashmere, wool and carpets
How do dehumidifiers work?
There are two main types of dehumidifiers that work in slightly different ways: desiccant dehumidifiers and compressor (also known as refrigerant) dehumidifiers. While all dehumidifiers have the same aim, which type you go for will depend on where and how you will use it.
Desiccant dehumidifier
Desiccant dehumidifiers extract water using an absorbent material to draw moisture from the air. Then an internal heater warms it so the moisture condenses and drips into the tank below.
The advantage of this type of dehumidifier is that it works well in warm and cold spaces. The only downside is that they tend to release warm air into a room, which you may not want in an already-heated home. However, they are ideal for a garage, loft or conservatory during colder months as they can operate below 10 degrees, unlike a compressor dehumidifier. They are also much quieter, so they might be a preferable option for you to use in a bedroom. Their main disadvantage is that they use a lot more energy and therefore cost more to run.
Refrigerant (compressor) dehumidifier
A compressor dehumidifier is the most common type in the UK as it works best in higher temperatures, such as in a heated home.
Compressor dehumidifiers work the same way as a fridge - a fan draws warm, damp air into contact with cold coils, and the water then condenses and drips into the tank.
The advantages of this type of dehumidifier are that they tend to be larger, more energy efficient and much more widely available. The problem is that they don’t work well in lower temperatures as the coils need to be colder than the room, or they start to freeze. Once that happens, a compressor dehumidifier focuses on de-frosting itself over reducing humidity, so they aren’t a great option for garages or cellars. They also tend to be much noisier, and depending on your noise-level preference, this can irritate people.
Read next: How to use a dehumidifier to dry clothes
Should you leave a dehumidifier on all the time?
You shouldn't usually need to run a dehumidifier constantly. Most modern models have a built-in humidistat, so you can set your preferred humidity level and the dehumidifier will cycle on and off as needed rather than running continuously.
If you're dealing with particularly high humidity, condensation or drying laundry indoors, you may need to run it for longer periods. If you're using a dehumidifier overnight, check the manufacturer's instructions and make sure features such as automatic shut-off when the tank is full are enabled.
Running a dehumidifier overnight isn't automatically cheaper – that depends on your electricity tariff. If you're on a time-of-use tariff with cheaper off-peak rates, running it during those hours could reduce the cost.
How to choose the best dehumidifier for your home
There are a few key things you need to consider when shopping for a dehumidifier, and various features you need to weigh up the importance of in terms of quality. Here are the sort of things you should be looking at when considering the best dehumidifier for your needs:
Extraction amount: It is essential to consider the maximum amount of moisture your dehumidifier can extract daily. It can range from anywhere from 500ml to upwards of 30 litres of water. Small units are fine for occasional use or a small area, such as a cupboard or study. Around 12 litres is suitable for a small flat, medium-sized room or a mild damp problem. Up to 16 litres is best for a larger room or one used regularly for washing or cooking, and units with a capacity of up to 20/30 litres can be used to dehumidify whole homes.
Water tank capacity: This is how much water the unit can hold, ranging from around 250ml to six litres. The smaller the dehumidifier, the more regularly you’ll have to empty the tank, though some larger models have a continuous drainage option through a hose.
Humidity levels: Relative humidity (RH) should sit between 30 to 60%, and most models have a built-in humidistat to keep the room at your chosen level. Devices with an auto-setting monitor adjust the moisture levels in the room, which can save on electricity.
Control panel: More basic models come with a manual control that turns on and off, while others have digital displays with more features, such as a timer and laundry drying mode, which removes excess moisture from drying laundry indoors and dries your clothes quicker. It can be a cheaper alternative to a tumble dryer, and an automatic shut-off and humidistat are also handy features.
Fan speeds: Some dehumidifiers have just one speed for continuous drying, limiting your control. Whilst others have up to three, which is advantageous if you want to adjust it for faster drying or put it on a lower (and possibly quieter) setting.
Portability: A model with a handle or wheels/castors (or both) will be easier to move around, especially if you buy a large, heavy dehumidifier. If you’re only ever going to use the dehumidifier in one room and won’t want to put it away much, this might not be so important to you.
Noise: A dehumidifier's noise levels can fall between 34dB to 60dB - 34dB being a whisper and 60dB being the same as a normal conversation. If you choose to run your dehumidifier at a lower fan speed, it will make less noise but may be less effective. Think about where you are using it and whether it will disturb you.
Cost to run: This will depend on your energy tariff, how you use the device, and how much power it uses. Check the power usage, which can range from around 22 to 600 watts - newer models tend to be more energy-efficient, for example, using 2.45p per hour based on 15.2p/kWh. Using a timer and humidistat will ensure it only comes on when needed. Desiccants tend to use more energy than refrigerants but are more powerful.
How much does a dehumidifier cost to run?
The cost entirely depends on the dehumidifier's wattage and current energy prices. We've given a cost-per-hour estimate for each dehumidifier on this list, and they range between 3p and 12p per hour. Smart Energy Tools' energy cost calculator allows you to work out how much different appliances cost to run.