What does a dehumidifier do – and does your home need one?

You may have heard of the benefits of a dehumidifier, or perhaps just know of their existence, and have wondered what exactly does a dehumidifier do?

Along with HVAC systems and air purifiers, the best dehumidifiers improve our air quality at home by tackling the humidity levels (or RH, relative humidity) indoors. Doing this can improve your health, protect your property, and create a more comfortable environment in the house.

So, what does a dehumidifier do, and how do they work? We spoke with the experts on dehumidifiers and air quality to find out whether or not you should consider owning one.

What does a dehumidifier do?

Like the name suggests, dehumidifiers lower humidity levels, thus 'dehumidifying' the space. Humidity is caused by water vapor in the air; indoors, this can be caused by boiling water, breathing, and lack of ventilation, whereas outdoors, it's caused by heat evaporating water from bodies of water.

High humidity levels indoors encourage the growth of mold and dust mites, both of which affect our health through triggering viruses and symptoms of allergies and asthma. It's generally a sign of poor air quality when humidity levels become too high.

'Dehumidifiers improve indoor air quality by decreasing the moisture in the air, which may contribute to a stuffy environment, odors, and mold-causing bacteria to linger,' explains Glenn Wiseman, technician and manager at Top Hat Home Comfort Services.

'Most people use dehumidifiers in their homes to extract excess moisture from places that they don’t want it to linger, [helping] to prevent mold growth in areas that are regularly moist like bathrooms, kitchens, basements, crawlspaces and utility rooms,' says Bethany Uribe, dehumidifier expert from ASAP Restoration.

'A dehumidifier also helps to protect property against excess moisture and is commonly used in homes where a subterranean level has trouble with removing excess water vapor from the air,' she adds. 'A mold outbreak can wreak havoc on a building if not addressed quickly, and by preventing mold from having the water it needs to survive, a dehumidifier helps to prevent contamination in the first place.'

As well as providing health benefits and protecting our homes, dehumidifiers make our indoor spaces more comfortable. 'Wet air tends to feel thicker and hold heat more readily than dry air,' says Bethany. Dehumidifiers can make the air feel cooler, less stuffy and generally more pleasant.

According to the EPA, humidity levels (indoor relative humidity, RH) should be between 30-50%. Low humidity levels can dry out the body, particularly the nose, throat and skin, leading to an increased risk of catching viruses. For this reason, dehumidifiers only extract a certain amount of moisture from the air.

How long it will take a dehumidifier to dry out a room will depend on the cause of the moisture, the size of your space, and your dehumidifier.

How does a dehumidifier work?

'Essentially, a dehumidifier pulls water vapor out of the air by condensing it and collecting it in a receptacle,' explains Bethany. '

'A fan takes the wet air and pushes it over evaporator coils. These are filled with a refrigerant condensed liquid. When the wet air passes over the cooler coils, its capacity to hold the moisture is reduced. This then causes the moisture to be deposited through condensation and collected in the reservoir.'

When the reservoir is full of water, it must be emptied either by yourself or through an integrated draining system. It's one of the many things I wish I knew before buying a dehumidifier.

Do you need a dehumidifier?

A humidistat will tell you if your humidity levels are too high, but you can generally tell if your air feels warm or stuffy, your sinuses get congested, or there's mold growing. If so, you should consider one, or at least look into DIY dehumidifers.

In the summer, a dehumidifier can make your home a safe space from the outdoor humidity levels, which are at their highest all year. Equally, in winter when we use the heating and dry our clothes indoors, dehumidifiers will remove all of that excess moisture from the air.

Also, as Bethany puts it, certain people should consider investing in one for the sake of their health, one of the more surprising uses for a dehumidifier.

'For people that have compromised immune systems, the elderly, or children, a dehumidifier can help to prevent mold contamination by extracting the moisture that mold needs to grow from the air,' she says. 'It also helps by capturing the mold spores floating around in the air while condensing the water vapor.'

If you do decide to get a dehumidifier, consider what your home needs. If humidity levels are high across your home, it might be worth investing in multiple for the most effective coverage, or, one that can easily be moved from room to room. Consider as well the size of the water tank: the smaller the tank, the more frequently you'll need to empty it.

'If you only have one dehumidifier for your home, place it in the room with the most humidity, usually the basement or the attic. Also, ensure you have an adequate draining system for your model or that the water collection container is level to avoid overflow and spillage once it is full,' advises Glenn.

Learn about the incredible difference a dehumidifier made to our writer's terrible window condensation.

Below are some dehumidifiers I'd personally recommend in a range of sizes and budgets.

Compare the differences between dehumidifiers vs air purifiers, where we go into more detail on the benefits of each. And for more air quality help, consider one of the best air purifiers.