Dehumidifier buying guide

If your home has an issue related to humidity levels, you will have to make efforts to regulate the amount of moisture in the air. One way of doing this is with a dehumidifier which you should select based on the following factors:

• the surface area or volume of the room in square metres;

• the air flow rate: the higher the number, the more efficient the device;

• the moisture extraction capacity: refers to how many litres of water extracted over a 24-hour period and depends on the rate of moisture in the air.

For even greater comfort, you might want to consider:

• a humidistat to control humidity rates automatically;

• a quieter model to avoid disturbance.

If you are looking for a dehumidifier that will run unmonitored – such as in a holiday home – you should consider the following options in addition to capacity and room size:

• hot gas defrost dehumidifiers continue to work below 15°C and are around 30% more efficient than other models;

• a moisture extraction system will allow you to connect a hose attachment to your device in order to drain the water directly into a sink or drainage pipe.

Moisture absorbers

If you're looking for a cost-effective and convenient way to reduce humidity in a smaller room, you could consider a moisture absorber. These little units are inexpensive and efficient, though you will have to empty the tray and refill the tabs every so often. They are best suited to rooms measuring up to 12 m².

A certain amount of humidity is essential for our comfort – but there are limits. A humidity level that is too high will encourage mould growth on ceilings, walls and furniture, and may cause wallpaper to peel. High levels of moisture in the air can also exacerbate health problems such as asthma, chest infections, rheumatoid arthritis, and so on.

Some rooms, such as the kitchen or the bathroom, are naturally exposed to a greater degree of moisture from cooking vapours, tumble dryer exhausts, etc. A dehumidifier is the ideal solution! Simple, efficient and economical, these devices allow you to dehumidify the air, making it healther to breathe.

Dehumidifiers can also be used to speed up drying during renovation work (i.e. painting, varnishing) or after water damage, and to sanitise crawl spaces. They will also help you save energy as moist air requires more power to heat than drier air.

There are two main types of dehumidifier: compressor (or refrigerant) dehumidifiers and dessicant (or absorption) dehumidifiers.

Compressor or refrigerant dehumidifiers

Efficient, compact and mobile (when mounted on wheels), this is the most common type of dehumidifier for domestic use. A fan is used to draw damp air into a condenser (a coil cooled by a refrigerant gas, compressed by a compressor). The air is cooled and the extracted moisture is sent into a tank. The dry air is then reheated before being returned to the room. These dehumidifiers work best in a warm environment and are effective in very moist rooms. However, they are fairly noisy and can be expensive.

Dessicant or absorption dehumidifiers 

This type of dehumidifier uses a fan to pass the air through a desiccant wheel (traditionally made of silica gel) which has considerable moisture absorption properties. Though quiet and fairly cost-effective, these machines are less widely used in a domestic context.

However, for normal use at 20°C and 70% humidity, these dehumidifiers actually do a better job than condensing dehumidifiers, which are generally tested by manufacturers under more extreme conditions, e.g. 30°C and 80% humidity.

Moisture absorbers are a type of absorption air dehumidifier that do not require any installation (no electrical connection). They consist of a plastic tray (which comes in several sizes) containing a sachet of silica gel or special tabs which are used to absorb moisture and transform it into water which is then collected in a tank.

While they are convenient and cost-effective, their lifespan is limited (about 2 months) and you will need to empty the tank regularly. In addition, moisture absorbers are only suitable for small spaces with minor humidity issues.

Before considering which model to purchase, you must first determine the exact nature of your needs. To do this, you must evaluate:

• The volume of air to be dehumidified;

• The existing humidity level;

• The temperature of the room; the cooler the space, the more efficient the dehumidifier;

• Any moisture sources present in the room; note that the capacity of your dehumidifier must exceed the quantity of moisture produced in the room. For example, a room with a swimming pool must have an evaporation rate lower than the extraction capacity of the dehumidifier.

Once your needs have been established, you then need to estimate the necessary air flow rate, extraction capacity, range, humidity and noise level of your device. Secondary criteria such as aesthetics, portability and additional features can then be considered.

Air flow rate

Air flow rate is an essential factor to take into account. It's defined as the amount of humid air that the dehumidifier is able to process over a certain period of time (per hour or minute). The higher the airflow rate, the more efficient the dehumidifier. This value represents the device's capacity to renew the air.

Extraction capacity

Extraction capacity is the number of litres of water that your dehumidifier can extract over a specified period of time (hours or days). Allow for 5–30 litres per day for domestic use in a damp room of average volume.

Room size

Of course, the size of the room will also determine the type of dehumidifier you go for. This is measured in square metres for surface area or in cubic metres for volume.

Humidistats

Humidistats or humidity regulators are manual or electric control systems used to control your desired humidity level. As a reminder, the ideal indoor humidity rate is around 45-60%. Electric humidistats allow you to control the level of humidity in the air by automatically switching on and turning off your dehumidifier when a certain level is reached.

Noise level

The level of noise that your dehumidifier emits is another important factor to consider; a good dehumidifier should be felt and not heard! Moisture absorbers are, of course, the quietest choice. The noisiest option is compressor dehumidifiers, the air flow rate of which will detemine just how noisy they are (the higher the rate, the noisier the device). You'll have to find the right balance between efficiency and noise!

Hot gas defrost dehumidifiers

When used at temperatures of around 5 to 15 °C, hot gas defrost dehumidifiers are around 30% more efficient than other dehumidifiers equipped with a defrost system (with the same power rating). It's worth nothing that, no matter the type of defrost system, these dehumidifiers will offer similar performance at temperatures over 15 °C. Defrost systems are recommended for use in unheated properties.

Design and portability

The design of your dehumidifier may not be an essential factor but if you can find an attractive or more discreet model, all the better! That being said, most dehumidifiers look fairly similar (with the exception of those designed for industrial use).

Even if you don't plan to move your dehumidifier often, it's always nice to have the option. Dehumidifiers on wheels are ideal for enabling easy movement from one room to another.

Dehumidifiers may come with a range of additional features, including the following:

• auto shut-off: the dehumidifier will automatically turn off when the water tray is full. An LED light will indicate when the tray needs to be emptied.

• a timer or programmer to programme when your dehumidifier turns on and off;

• external water extraction: by connecting a hose to run into a sink, for example;

• 3-speed fan: allowing you to change settings according to your needs;

• a special drying mode allowing you to dry fabrics and speed up laundry drying in the wintertime;

• a night mode for quieter operation;

• a child lock allowing you to lock the control display;

• a wide operating temperature range (generally from 5 to 35°C);

• a clogged filter warning light;

• continuous mode: can be activated as need (the device constantly dehumidifies the air regardless of humidity rate).

A dehumidifier must be efficient, reliable and adjustable. These days, it's possible to combine all these characteristics with aesthetics in a compact, silent and attractive model!

Moisture absorbers offer a great solution for low-humidity rooms and small spaces. While buying a dehumidifier is a good measure to avoid excessive moisture, remember there are solutions to reduce the amount of moisture produced in the first place, such as:

• damp proof paint for damp rooms (kitchens and bathrooms);

• insulation, the first barrier against heat loss;

• heating, as under-heated homes can encourage humidity;

• airing out damp rooms or renewing the air with an air conditioning system;

• cooker hoods in kitchens, etc.

Before carrying out any maintenance or cleaning tasks, you must unplug your dehumidifier.

Cleaning the grids and casing

The air inlet and outlet grids can be cleaned using a vacuum cleaner fitted with a small brush nozzle. This will allow you to collect the dust directly. Otherwise, you can use a normal brush.

The outer casing can be cleaned using just a bit of soapy water. Be sure to rinse well and wipe down afterwards.

Cleaing the air filter

You must clean your air filter of any impurities (pet hair, dust, etc.). Consult the manufacturer's guide for instructions on how to remove the filter, then rinse it using clean water.

Cleaning the water tank 

The water tank must also be cleaned. After disassembling your dehumidifier, you simply need to rinse it under water and wipe it down. Cleaning this part is essential in order to prevent mould and bacteria growth.

Preparing to store your dehumidifier

If you don't plan on using your dehumidifier for a certain period of time, you should follow these four steps before storing it away:

1. Empty the tray no more than 24 hours after its last use.

2. Clean the casing, air grids, filter and tray.

3. Wind up the power cord then cover up the device with a protective cover or put it back in its original packaging.

4. Store the device away from any sources of humidity.

More information

• Dehumidifiers: the advantages and disadvantages

• Portable air conditioner buying guide

• Air conditioners: advantages and disadvantages

• Fan buying guide