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An Introduction to Dehumidifiers

Date posted: 29 November 2016

Lots of households in Britain struggle with condensation problems or unpleasant signs of dampness such as mould. Some homes even battle with a musty odour, uneven floor boards, or wet stains on the walls and ceilings. But in many cases the regular use of a dehumidifier can significantly reduce these problems, creating a more pleasant living environment.

There is always water in the air, whether you are inside or outside your home – but the amount of water varies significantly depending on a wide range of factors. Lots of our regular daily life activities contribute to the amount of water in the air, including cooking, showering, clothes washing, boiling the kettle, and even breathing! Uncovered water containers such as fish tanks also contribute to the amount of water in the air.

What does a dehumidifier do?

These machines are designed to control a room's humidity level by removing excess moisture from the air – until relative humidity is reduced to the desired level. Relative humidity is expressed as a percentage, and is a measure of the water vapour in the air relative to the amount the air could hold if it was saturated. When relative humidity reaches 100% it is at the "dew point", which means the air is "full" of water -- and that water will start to condense onto any surface (such as windows and walls). The general consensus is that a relative humidity of around 50% is optimum for your home, creating a comfortable environment and protecting your home and belongings.

If you choose a high quality unit, once it has achieved your chosen humidity level it should be able to automatically maintain that level without any input from you.

What are the main benefits of using a dehumidifier?

Controlling humidity levels can bring various benefits, including making the air more comfortable, reducing signs of dampness such as condensation on your windows or mouldy patches on walls, and helping to control the dust mite population in your home.

A dehumidifier dries out your room, extracting damp from its contents and any fabric on which mould and mildew will grow – preventing damp from recurring. If your dehumidifier is set to maintain relative humidity at 50% or slightly lower, the air will be too dry for mould and mildew spores to develop. 

Some people also claim that dehumidifiers provide health benefits such as reducing allergy symptoms. Excess moisture in a room creates the perfect breeding ground for mould, mildew, bacteria and dust mites, all of which can trigger allergies – causing respiratory problems, itchy eyes and skin, and various other unpleasant symptoms. 

What's the difference between desiccant dehumidifiers and refrigerant dehumidifiers?

Dehumidifiers come in many different sizes and at a variety of prices, but there are two main types you will need to choose from before deciding on a particular model. Each type works in a different way and, as a general rule, each type tends to be suited to a specific type of environment:

  • Refrigerant (or compressor) dehumidifiers: These work by drawing in air through a filter and over cold coils. The water then condenses on the cold coils and drips into a water tank. The general claim is that refrigerant dehumidifiers are most effective in higher temperatures and higher humidities, therefore they tend to be the preferred choice for most lived-in homes in Britain.
  • Desiccant dehumidifiers: These work by using an adsorbent material that draws water from the air. The material is then heated up so that the moisture drips into the water tank. This type of dehumidifier is said to work best in lower temperatures, such as in a garage or a conservatory. They tend to use more energy than refrigerant dehumidifiers because of the heat required to warm up the adsorbent material.

For more information , please see our article on the main differences between refrigerant and desiccant dehumidifiers.

Choosing your dehumidifier

Once you have decided which type of dehumidifier best suits your room, you will need to consider the following:

  • Capacity: make sure the unit you select can cope with the space in which you plan to use it 
  • Energy efficiency: Energy-efficient models are better for the environment and for your household budget.
  • Features: check that the design is user-friendly, incorporates a digital humidistat, a timer that you can set/programme, wheels to help you move it from room to room (if appropriate), and full collection bucket overflow protection. You may also want to find out how quiet the unit is whilst it's running.

Getting the most out of your dehumidifier

  • Start by vacuuming the room to avoid distributing dust around the room, or clogging up your dehumidifier's air filter (if it has one). 
  • Position your dehumidifier away from furniture, walls and curtains.
  • The majority of dehumidifiers now incorporate an automatic humidistat. Set this to 45-50% humidity to achieve optimum comfort. Automatic humidistats monitor the moisture in the air, switching the machine on and off as necessary in order to maintain the humidity level you’ve set it to.
  • Keep all of the room's doors and windows closed while the dehumidifier is running.
  • Each time you use the machine, empty out all of the collected water before using it again, or moving it to a different room. You can reuse this to water your plants!
  • Vacuum the dehumidifier's air filter regularly, if it has one – and if it gets very dirty you may be able to wash it (although it's vital to read the manufacturer’s instructions first to make sure this will not damage the filter).

How long will it take to make a difference?

If you hire a dehumidifier that is large enough for the room you are using it in. and there are no existing damp problems,  the dehumidifier will usually reduce the humidity to your preferred level within a matter of days. If you have significant damp problems or have suffered a flood, however, you may need several dehumidifiers to start off with, potentially used alongside air movers and other specialist equipment.

Further tips for beating condensation problems

There are some other steps you can take, alongside using your dehumidifier, to help beat condensation and mould. Try:

  • Sealing any cracks in your walls with a caulk or sealant.
  • Switching on an extractor fan (or at least opening a window) whenever you have a bath or shower.
  • Wiping down the bathroom walls and floors after you have a bath or shower.
  • Drying wet clothes outside, or at least hanging them to dry next to an open window.
  • Using the extractor fan on your cooker hood whilst cooking, to help extract steam.

Tackling serious damp problems

If you find you are still struggling with condensation and damp problems despite your best efforts:

  • Check for leaking pipes or appliances (e.g. washing machine, dishwasher, etc).
  • Ensure your tumble dryer is vented correctly to the outside.
  • Unblock any clogged gutters and check that down spouts are directing rainwater away from the house.
  • Consider installing a damp proofing course to deal with any structural rising damp.

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