How Do Dehumidifiers Work?

In our line of work, we are often asked how do dehumidifiers work and what they do to the air to be able to extract moisture (humidity).

In this article, we’ll take a look at the different types of dehumidifiers, how they work, and how you can get the most out of them.

But first of all, it’s probably an idea to discuss humidity itself, and what it is.

Explaining humidity

Although humidity isn’t something that we think about on a daily basis, when it’s in our homes it can make a big difference on cleanliness and health.

Humidity is the amount of water vapour in the air, and the more humidity you have in your home, the greater chances you have of developing mold and other issues.

Humidity levels can increase if you don’t have proper ventilation in your home, and a sign that there is too much humidity can be found in the form of condensation on both windows and walls.

It is thought that indoor humidity levels should be around 30% to 50%, with the ideal level of indoor humidity often being cited to be around 45%.

At this level, it makes it hard for mites and mold to thrive in indoor environments.

Getting rid of excess humidity

Getting rid of excess humidity

Excess humidity in your home

You can test how much humidity you have in your home by going to the local supplies shop and purchasing a simple hygrometer.

With this small device, you can test how much humidity is in your home, which will be shown as a percentage figure.

It’s worth remembering that humidity will vary between summer and winter, with there generally being more humidity during the summertime.

If you find that your home has too much humidity in it, aside from improving ventilation, you could of course purchase a dehumidifier to help with the issue.

But how does a dehumidifier get rid of humidity?

First of all, it’s important to know that there are two different kinds of dehumidifiers for the home.

How do Refrigerant (Compressor) Dehumidifiers work?

Otherwise known as refrigerator dehumidifiers, these dehumidifiers work by cooling the air to remove the moisture.

  1. The first step of the process is done by the unit sucking air through its grilles on the side or front of the machine, which is done by an electric fan.
  2. Once inside the unit, the warm air is passed over very cold pipes which are regulated by a special coolant. While being passed over, the water vapour is cooled and turns into liquid water, which then drips off the pipes.
  3. The dry air is then passed over a heating element to return it to its original temperature before it is pumped back into the room.
  4. The collected water inside the machine falls into a tray or tank at the bottom of the machine. Usually, a plastic float is present, which tells the machine when the tank is full.
  5. Tripping an electric switch once at the top, the fan is switched off and an indicator light is turned on, indicating that the machine needs emptying.

Some machines come with a hose attachment which means that they are continually emptied as the unit works.

How do Desiccant Dehumidifiers work?

It’s worth noting that not all dehumidifiers work by the way of refrigeration, as you can also purchase desiccant dehumidifiers, which work by simply “mopping” the moisture from the air, a little like a sponge.

Generally, desiccant dehumidifiers work via either absorbing the water, where it soaks right into a desiccant material or by adsorption, where the water is collected on the surface of the material.

  1. The desiccant dehumidifier starts by drawing air through a duct, where it is then passed through a large rotating wheel composed of water-absorbing (or adsorbing) material. It is this material that removes the humidity from the air.
  2. The air is then drawn by a fan operated by an electric motor and the air is blown back out into the room.
  3. The air duct is often kept hot by an electric heating element, which also heats the airspace within the rotating wheel to dry it out.

Are either kind of dehumidifier suitable for my home?

As both dehumidifiers work differently, it’s important to know and understand the different attributes that each kind provides, as some might not be suitable for your home or room, depending on how warm the overall temperature is.

Air temperature below 15°C (59°F)

When it comes to using a dehumidifier in a basement or garage, dehumidifiers will often work in cold temperatures, so it’s important to know that such an environment would be better suited to desiccant dehumidifiers.

This is due to the fact that the inside of a compressor dehumidifier needs to be colder than the air in the room in order for it to work efficiently.

As you can imagine, the colder the room is, the colder the environment within the unit needs to be so that it can extract moisture from the air.

If the room temperature falls below 10°C (50°F), it means that the components within a compressor dehumidifier will be close to freezing, which means that ice could form on the cooling coils.

Most compressor dehumidifiers will spend two-thirds of their time defrosting themselves when faced with temperatures below or around 10°C (50°F).

Understanding capacity

Different models of dehumidifiers will, of course, have different capacities. Although most people presume that the capacity of a dehumidifier relates to the amount of water that a dehumidifier can hold, it actually relates to the amount of moisture that a dehumidifier can take out of the air during a 24 hour period.

It’s worth remembering, however, that just because a dehumidifier can remove a certain amount of water over a 24 hour period, it does not mean that they have to be left running for such a time.

Your average house, for example, might only need six or twelve-hour operational periods so that the home attains the desired humidity level.

Are dehumidifiers loud?

Are dehumidifiers loud?

As with any kind of machine, dehumidifiers tend to make noise, which is largely attributed to the fans sucking in and pumping out the air.

Depending on the make and model, you will find that some dehumidifiers are of course louder than others.

You can also pick up some that are designed to be especially quiet, which is useful if you have a young family.

It is generally thought that units that exhaust air out of the top of the machine have a noise disadvantage over those that pump air out of the side.

It’s worth noting, however, that on a general basis, desiccant dehumidifiers tend to operate at a lower volume than compressors, due to the fact that compressors tend to have more moving parts.

That said, compressor technology is often in a state of continual advancement and some of the newest compressor units are able to operate at very low volumes.

Overall, you tend to find that desiccant dehumidifiers on low fan speeds can operate at around 40 dB, and it would be hard to find a compressor dehumidifier below this noise level, although it has been noted that some Mitsubishi units are able to achieve this.

It is often thought that middle and top fan speeds of desiccant machines operate at similar noise levels as compressors, and for those that need quiet operating machines, it is important to note that desiccants will always have the option to switch to quieter modes.

Do dehumidifiers take a lot of energy to run?

Again, this will depend on the size of the dehumidifier you buy, as well as the type, model, and brand.

But this is an important question, and generally, it is important to know that generally, compressor dehumidifiers are cheaper to run.

Look out for a dehumidifier that comes with the Energy Star rating if you are based in the US. This means that it will be 15% more energy efficient than a dehumidifier that is not rated.

Energy Star Rating

Energy Star

That said, a lot of people use dehumidifiers in winter months, and the extra energy used by a desiccant dehumidifier is released into the room as heat. Many people, therefore, find that they are able to turn their thermostat levels down by one or two degrees, which helps save money when it comes to heating bills.

When researching a dehumidifier, it is important to look at the unit’s wattage, so you can understand its power consumption. Although (generally speaking), this won’t tell you how efficient a dehumidifier will be, the higher wattage often means that the machine will be using more electricity and removing more moisture from the air per hour.

It is generally thought that a domestic dehumidifier, depending on both the amount of humidity being treated and the size of the room in which it is located, would cost between £10 to £20 to run per month.

Often thought of as “energy-intensive appliances” by experts, a dehumidifier that is operated throughout the year could cost around £100 per year, which is the equivalent of around 9% of the average energy consumption of a typical home.

For further information read our ‘How Much Does it Cost to Run a Dehumidifier?’ guide.

Can a dehumidifier stop the spread of damp and mould? 

Yes, A dehumidifier will prevent the spread of mould and dampness in your space. If you notice signs of damp in your home, like condensation in your windows, try and dry them – this may prevent the need for a dehumidifier. 

Tips on how to prevent dampness

  • Open a window or use an extractor fan when you take a shower or bath.
  • Wipe any moisture from your walls after a shower or bath
  • Seal any cracks with a good quality sealant
  • Place wet clothes to dry near an open window, and where possible, try and dry your clothes outside. 
  • Use an extractor fan when cooking on a hob

Find out how to spot mold and damp with our Quick and Easy Ways to Spot Damp Inside the Home.

How does continuous drainage work?

Most dehumidifiers contain a water tank that collects water that is removed from the air. It’s likely that you’ll need to empty the tank on a daily basis. If the tank is full, the dehumidifier will automatically switch off, so make sure you check this regularly. Some dehumidifiers can be set up for continuous drainage. This means that you’ll need to attach a hose to the dehumidifier and run this down to the floor level drainage. In most cases, the dehumidifier will come equipped with a hose. You’ll need to make sure the dehumidifier is slightly raised from floor level for this to work.


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