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How to Choose a Household Dehumidifier and Get Rid of Damp

Rik is a father, training specialist, and qualified physics teacher who is passionate about learning and development.

Humid conditions lead to nasty mould growth.

Humid conditions lead to nasty mould growth.

Why Do I Need a Dehumidifier?

During cold spells in winter, it is sensible to keep windows in the home tightly closed. However, modern houses and flats are far better insulated and sealed than in the past so, with no air conditioning, this results in a gradual build-up of moisture inside the home.

Common signs of damp are when the insides of your windows, even if double-glazed, are wet, and mould starts to appear around windows or ceilings, particularly in bathrooms.

This moisture comes from washing machines, showers, cleaning and even the breathing of the occupants of the house. Yes, even your sleeping cat and the guinea pig are contributing to the moisture build-up.

If you don’t have air conditioning, then the humidity (moisture in the air) in winter will often increase to levels well above 50%. The house will become damp and black mould and mildew will start to grow.

For maximum comfort, humidity in the home should be from 30% to 50%. Anything over 50% encourages pests such as clothes moths, dust mites, fleas, cockroaches and woodlice. Humid conditions may also lead to a musty smell and cause damage to furniture and carpets.

In addition, drier air feels warmer and less energy is needed to heat the home than when the air is too moist. On the other hand, if the air is too dry, with a humidity of less than 30%, then static electricity becomes a problem. And dry air can lead to a dry cough or respiratory problems.

How to Prevent Excess Humidity

Buy a domestic dehumidifier. There are plenty of models available to suit every size of home. The easiest way is to buy online. Most suppliers in the UK deliver free of charge.

A smaller, bottom-of-the-range machine can be bought on Amazon for around £100 ($150). Something suitable for a four-bedroom house would start from around £150 ($220).

There are two broad types of dehumidifiers based on different technologies:

  • Refrigeration dehumidifier
  • Desiccant dehumidifier

Refrigeration Dehumidifiers

Refrigeration dehumidifiers, the most common type, typically draw moist air over a refrigerated coil using a small fan. As a result, some of the water in the air condenses on the evaporator coils and drips into a collecting bucket. The dried air is then reheated to the ambient temperature of the room.

This process works most effectively with higher ambient temperatures and with a higher humidity. The process is less effective in a colder location. These machines work best at over 45 percent relative humidity, but this figure increases if the air is colder. In other words, refrigeration machines are ineffective in an unheated location in a cold climate.

Desiccant Dehumidifiers

This dehumidification process uses a humidity-absorbing material called a desiccant, which is exposed to the air to be conditioned. The humidity-saturated material is then moved to a different location in the machine, where it is "recharged" by removing the water absorbed from the air, typically by heating it. The desiccant is usually mounted on a belt or a rotating arm in order to move it within the machine.

Desiccant dehumidifiers are especially suited to lowering humidity at low temperatures. They are therefore effective for unheated locations in winter such as caravans, garages and outhouses or empty properties. These machines use more electrical power than the refrigeration type but do emit some heat as a by-product of the process, so raising the ambient temperature of the space being dried.

Typical compact domestic dehumidifer from Eco Air using the Desiccant Principle

Typical compact domestic dehumidifer from Eco Air using the Desiccant Principle

Features of Domestic Dehumidifiers

The advantage of a small portable model is you don’t need to have it fixed in one place. If a particular part of the house becomes too humid, then you can move the dehumidifier to where the problem is.

Tank Size

Dehumidifiers have a tank to collect the water. The bigger the tank the less often you need to empty them. These tanks typically have a minimum capacity of 2 litres. They also normally have a warning light that indicates when the tank needs emptying and automatically switches the machine off once the tank is full.

Drain Tube

Some machines have an alternative drain tube that enables the water to drain away rather than collecting in a tank. Remember that with a portable device it will not always be practical for it to drain externally, for example if temporarily located in the living room, hall or landing.

The drain tube works well, for example in a utility room, where you can insert the drain tube into the waste pipe used by the washing machine.

Energy Usage

It is worth comparing how much electrical power each machine uses and estimating the relative running costs. Generally the desiccant machines use more power than the refrigeration machines.

Weight and Size

Weight and size is worth considering. Is there room for the machine, and will you be able to manage to move it to other locations? A decent carrying handle is obviously another consideration when evaluating machines.

Also make sure there are electrical sockets available where you want to temporarily locate the machine. A smaller machine will typically weigh around 6 kg (13lb).

Typical control panel on a simple dehumidifier

Typical control panel on a simple dehumidifier

Extraction Rate

Find out how many litres of water a day the machine can extract. Typically, domestic machines will extract from 5 to 10 litres per day. Make sure the machine is suitable. Smaller models will handle a small flat, and bigger machines can comfortably tackle a 4/5 bedroomed house.

Laundry Mode

Dehumidifiers are great for drying clothes. Some machines have a laundry mode designed specifically for clothes drying. This continually extracts moisture regardless of the relative humidity of the room.


If you want to run your dehumidifier using a time switch, then make sure the model you use will auto-start. In other words, as soon as power is applied, it begins to extract moisture.

Other Features

Machines typically have more than one fan speed. Slower speeds are more economical and quieter, but obviously, the higher speeds will result in more rapid extraction taking place.

It is also worth checking the relative output noise of the machine. If you want to have it running at night in a bedroom, then make sure it isn't too noisy.

Also check the operating temperature required. If you want to extract moisture from an unheated area, then the desiccant models will give lower operating temperatures.

Typical humidifier water tank being emptied

Typical humidifier water tank being emptied

You Might Be in Need of a Dehumidifier

So what are you waiting for? If your home is showing signs of damp or mould then you need a dehumidifier. The easiest way to get one is to order online.

Compare the different models available. Amazon is a good place to start. Once you've found the model you fancy, then check using a price comparison site to make sure you get the best price.

Dehumidifiers are very easy to use and will start working straight out of the box. Just set the machine to your target humidity and switch it on! You might also want to buy a digital air humidity meter at the same time.

These start from around £6 ($10), including delivery, and are readily available on eBay and Amazon and enable you to check the humidity levels in different areas of your house.

This content is accurate and true to the best of the author’s knowledge and is not meant to substitute for formal and individualized advice from a qualified professional.


nicomp really from Ohio, USA on August 10, 2013:

I run mine every day of the year. It fills up twice a day in the humid Summer.

tipstoretireearly from New York on December 07, 2012:

I've just started using a dehumidifier in the winter to eliminate condensation on the windows. So far so good! Informative hub!