What is a Dehumidifier?

Dehumidifiers are appliances designed to reduce humidity from air in enclosed indoor spaces. By controlling the amount of moisture in the atmosphere, they serve to address issues such as mould and damp, peeling paint and wallpaper and general condensation. They are also essential items for those who bear allergies to particular mould spores as well asthma sufferers, for which certain airborne allergens related to increased humidity, can be triggers.

Taking a shower, opening the dishwasher, cooking and other daily household activities can all increase humidity levels. Not only can this damage your house and belongings, it also creates an ideal environment for bacteria, viruses, mites and fungi. Whatever way you look at it, high indoor humidity is an issue that needs to be tackled. Unless, of course, you live in a botanical garden – then things would be entirely different.

Here at Dehumidified we’re here to help you make a decision on the right equipment to buy, so check out our reviews or buying guides if you’re looking to purchase.

How Do Dehumidifiers Work?

At it most basic, a dehumidifier sucks in air, removes the moisture and then blows it back out again. Of course, it’s more complex than that so let’s elaborate on the basic principles.

There are two predominant types of dehumidifier: desiccant and compressor.


Compressor dehumidifiers, sometimes referred to as refrigerant dehumidifiers, suck in the warm air in a room that contains moisture. This warm air is passed over cold coils – or a refrigerated evaporator – in the same manner as cooling occurs in a refrigerator. As the temperature of the air is lowered, it condenses and the moisture drips into a receptacle within the unit. The air is then reheated to room temperature and blown back out into the atmosphere.

Compressor-driven dehumidifiers are limited by environment and will generally only function effectively between 5 and 30 degrees celcius. 15 degrees is generally considered as the temperature that yields optimum performance.

Some examples of popular compressor dehumidifiers are as follows:


Desiccant dehumidifiers are smaller than their compressor counterparts and are considered more durable and better value for money. They generally use Zeolyte to absorb water vapour, which is very similar in function to silica gel that is often packaged with products to prevent damp.

Air containing moisture is drawn into the dehumidifier and passed over a wheel that contains the manufacturer’s chosen dessicant. This absorbs water molecules from the air, which is then extracted from the wheel using an air heater. The dry air is then blown back out into the room.

Unlike compressors, desiccant dehumidifiers are not bound by temperature-related performance constraints. They function the same regardless of climate, although there are obviously extremes that would affect the unit’s general activity. This reliability is what makes the desiccant solution more suitable for European countries where the temperature may significantly vary throughout the year.

Some examples of popular desiccant dehumidifiers are as follows:

Do I Need One?

The optimum level of humidity in an environment is 50-55% relative humidity. This is a ratio pertaining to the level of water vapour in the air relative to the maximum amount of moisture the air can accommodate. This varies depending on temperature. Hotter air, for example, can hold more water vapour than cooler air. Relative humidity should not be confused with absolute humidity.

Technicalities aside, air humidity can be measured can be measured using a hygrometer. If you’ve not got access to one of these (they’re quite cheap and you can easily pick one up) you may just want to look for obvious signs of increased humidity including condensation on windows, a musty smell and perhaps some aesthetic considerations such as peeling wallpaper. If you’re seeing any of these tell-tale signs, then it may be time to invest.

Choosing a Dehumidifier

There are countless dehumidifiers to choose from and what you opt for depends on your needs. Whether you’re looking for. A general rule is that one will set you back around £75-£175 depending on type and size.

For a more detailed overview of, check out our buying guide.