What is the Difference Between a Dehumidifier and an Air Purifier?

What is the Difference Between a Dehumidifier and an Air Purifier?

It’s quite easy to get dehumidifiers and air-purifiers confused. While they may look similar externally and both do suck stuff out of the air, they really have two completely distinct functions. They’re not a small investment either and so it’s very important that you get the right machine for what you need. Get the wrong one and while it may look good, you’ll have wasted your money because it won’t be fulfilling the task you bought it for. As well as being quite a few quid lighter in your pocket, you’ll also still be stuck with the original problem.

Read on to find out the basic differences between a dehumidifier and an air-purifier and how they do the job they do.

LEARN MORE: You can read more about air purifiers and the best sellers in our guide here and dehumidifiers in our guide here.

So which one does what?


Dismantle the word dehumidifier and you’ll find the answer to this machine’s purpose. Yes, the keyword is – humid. If you have a damp problem in your home then this is the device you should be considering purchasing.

Surprisingly, the atmosphere holds a lot more moisture than we actually give it credit for and some geographical locations are more problematic than others. Sometimes damp can be so bad, you can even end up having a home that smells like a pair of smelly football socks which haven’t been changed all season. That humidity in the air, although it’s invisible, can cause not only damage to your home, but to your health too.

Dehumidifiers are also a good solution if you have a glass conservatory or bathroom which suffers from condensation. If you’ve found mould and mildew are sprouting in certain poorly ventilated corners of your house, then checking out dehumidifiers means you’re on the right track to curing the problem.

How does a dehumidifier work

Think of a dehumidifier as a technologically driven sponge. It’s been manufactured specifically to remove as much moisture from the air as possible. Once you’ve got it switched on, believe it or not, it won’t work unless you do, it’ll begin to draw air in through strategically placed vents. Vent sizes vary with different machine designs so don’t expect them all to look the same.

The air circulates inside the dehumidifier and passes over an ice cold metal grill which is similar to the internal workings of a fridge. The coldness turns the moisture in the air back into water which subsequently drips down into a catchment container. The dehumidified air is then expelled out of the machine through a different vent and back into the atmosphere of the room where you’ve placed it. Sounds pretty simple really, doesn’t it? But as you might be able to imagine, dehumidifying is an ongoing process and it isn’t going to happen in five minutes.

Most dehumidifiers are capable of measuring the level of humidity in the air automatically and aim to hit a target range of between forty to sixty percent. So if your damp problem is serious, be patient. You’re going to have a lot of water to empty from the container of your dehumidifier, but it’ll be worth it in the end. Most dehumidifiers will switch off automatically when the water collection container is full. That means you’re able to leave them running when you’re away from home and won’t have to worry about returning to find the house flooded.


The key word in air-purifier which defines its function is – purify. Unlike the dehumidifier, it doesn’t remove moisture from the air, but rather many different types of toxins.

If you suffer from allergies like hay fever or have asthma triggered by dust mites, this is the machine you should be looking to invest in. They’re also good for filtering cigarette smoke out of the atmosphere as well as pollution from traffic, which if you live near a busy main road is quite often present in your home without you realising it. So if you’re walking around your house sneezing, wheezing or just feeling nasally stuffed up, you’re reading about the right product.

Even though you can’t see the pollutants in the air, you know there is something there because you’re reacting to it. They also deal with some things which may initially seem quite gross but sadly are a fact of life. If you have a dog or cat, they shed not only hair but tiny pieces of skin which can be harmful to your health. Human’s also shed skin cells. A good air-purifier can deal with all of that as well as removing mould spores and cold and flu germs from the air.

If you work in a busy office, it can be well worthwhile investing in a desk-sized model for those awkward moments when your work colleagues have a sneezing fit. You’ll get better protection with your own personal air-purifier than if you just turn your head away or don’t breath in. Right now, an air-purifier is starting to sound like a good investment, isn’t it?

How does an air-purifier work

Air-purifiers are, in a basic way, a bit like vacuum cleaners with increased effectiveness. They suck up particles from the air, rather than the carpet, before regurgitating lovely clean air for you to breath. Equipped with sensitive monitors internally, similar to a sniffer dog’s nose, they are capable of registering the level of pollutants in the air and begin working automatically if the reading is high.

While it may be difficult to believe they can actually remove such microscopically small specks from the air, they really do. In the best air-purifiers, the magic is worked by something called a HEPA filter, or high-efficiency particle absorber, which sits inside the air-purifiers inner workings.

This amazing filter is made of incredibly dense glass fibres which have gaps between them that are anywhere up to five hundred times finer than a human hair. When the air-purifier is functioning, a fan draws air inside and it then passes through the filter which catches just about everything, including a cold germ, before the filtered air is re-released into your room. Considering their efficiency, air-purifiers with HEPA filters don’t require much maintenance as the filter only needs changing every six months.

There are other types of air purifiers on the market which don’t have HEPA filters. Yes, they are more economical to purchase initially, but their effectiveness can be questionable and they’re not as efficient as those with HEPA filters.

Some air-purifiers have activated carbon filters. The stiff mesh, a bit like a thin black Brillo pad, is made of porous carbon and can capture a certain amount of pollutants from the air, but some allergens and a lot of germs are small enough to pass through the filter and so end up back in the room.

If you’re an asthma sufferer, you’ll want to consider avoiding any air-purifier which works by producing ozone. It’s possible they actually increase asthmatic symptoms rather than curing them. Ozone air-purifiers work by expulsing ozone gas into the air which then kills off the bacteria which produces bad smells. They don’t remove allergens or pet dander from the air but will exterminate mould spores.

You’ll need a good head for physics or chemistry to get a grasp of exactly how a negative ion air-purifier functions. Basically, it all boils down to how positives and negatives attract. A negative ion air-purifier produces ions which stick to the microbes in the air making them too weighty to float around. Yes, this type of air-purifier might remove allergens etc from the air, but it doesn’t remove them completely from the environment.

Air-purifiers which work with UltraViolet technology are great for zapping germs. Bacteria in the air which is drawn into the machine is killed off by the ultraviolet light inside. They’re ideal for sterilising rooms after bouts of sickness or used as a precautionary measure during flu epidemics. UV light on its own doesn’t deal with pollen, pet produced allergens or traffic pollution so this type of air-purifier are often produced with an additional filter system which increases its efficiency.


So now you know the difference between a dehumidifier and an air-purifier, we hope you’ll get the right one for the job.