Comparison
Dehumidifier vs air purifier: what each one does
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In short
A dehumidifier lowers humidity by removing water from the air, which tackles condensation, damp smells and slow-drying washing. An air purifier filters particles such as dust and pollen but does nothing to humidity. If your problem is wet windows or damp walls, buy a dehumidifier; if it is dust, an air purifier. Combined units do both at once.
Products for this job
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Meaco Arete Two 20L: intelligent humidity mode
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Pro Breeze 30L/day: humidity sensor and drain hose
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Ariston Deos 21S NET: set humidity by app
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Our verdict
Buy a dehumidifier if your problem is condensation, damp or washing that will not dry. Buy an air purifier if humidity is fine and you only want fewer particles in the air. Choose a combined unit with a HEPA filter if you need both in one room.
The two machines look similar, both sit on the floor and both move air through a filter, so it is easy to assume they overlap. They do not. A dehumidifier is about water: it takes moisture out of the air and puts it in a tank. An air purifier is about particles: it pulls air through a fine filter and returns it cleaner but just as humid. This guide explains what each one does and does not do, how to tell which problem you have, and when a combined dehumidifier with a HEPA filter is a sensible buy.
What a dehumidifier does
A dehumidifier draws room air in, removes water from it and blows the drier air back out. A compressor unit does this by chilling a coil below the dew point; a desiccant unit uses a moisture-absorbing wheel. Either way, the result is lower relative humidity, measured in % RH, and a tank of water.
Lower humidity means less condensation on windows and cold walls, faster drying of washing and fewer conditions in which mould tends to grow. A dehumidifier usually has only a basic dust filter to protect its coils, which is not designed to clean the air.
What an air purifier does
An air purifier draws air through one or more filters and returns it with fewer particles in it. Most use a HEPA filter, which traps fine particles such as dust, pollen and pet dander, and many add a carbon filter for odours. It does not remove water, so humidity, condensation and damp stay exactly as they were.
That means an air purifier will not stop windows streaming or walls going damp, and it will not help washing dry. If those are your problems, an air purifier is the wrong tool.
Side by side
The table makes the split clear. The only overlap is in combined models, which put a HEPA filter on a dehumidifier.
| Dehumidifier | Air purifier | |
|---|---|---|
| Main job | Removes water from the air | Filters particles from the air |
| Changes humidity | Yes, lowers it | No |
| Helps condensation | Yes | No |
| Helps drying washing | Yes | No |
| Filters fine dust | Only with a HEPA model | Yes |
| Needs emptying | Yes, or drain hose | No |
| Main upkeep | Wash filter, rinse tank | Replace filters |
When a combined unit makes sense
Some dehumidifiers now include a HEPA filter. Meaco lists the Arete Two 20L with an H13 HEPA filter alongside its 20 litres a day extraction, and De'Longhi sells AriaDry Multi models described as dehumidifier and air purifier in one. These suit homes that want both jobs done in one room, such as a bedroom with condensation, without buying two appliances.
The trade-off is that the purifier part only works while the fan runs. If the dehumidifier switches off because the room has reached its humidity target, filtering stops too, unless the model has a purifier-only mode. Check the manual for that before buying, and check what replacement filters cost and how often they are needed.
How to tell which problem you have
A cheap hygrometer, or the humidity reading on a dehumidifier, tells you most of what you need. If the room regularly sits above about 60 % RH, or you see condensation on windows in the morning, the problem is moisture and a dehumidifier is the answer. Our dehumidifier humidity settings guide gives targets by room.
If humidity is normal but you notice dust settling quickly or want to filter pollen, an air purifier fits. If both apply, a combined unit or one of each is reasonable.
- Streaming windows or damp walls: dehumidifier
- Washing slow to dry: dehumidifier
- Dust settling fast: air purifier
- Both: combined unit, or one of each
A word on mould
Neither machine removes mould that has already grown. A dehumidifier helps by lowering the humidity it needs, but existing growth needs cleaning, and persistent damp needs its cause found. See how to remove black mould for general cleaning steps, and speak to your landlord or a qualified surveyor if damp keeps coming back.
Frequently asked questions
Can an air purifier reduce humidity? No. An air purifier filters particles but does not remove water, so humidity stays the same.
Does a dehumidifier purify the air? Not on its own. Its standard filter only protects the coils. Models with a HEPA filter, such as the Meaco Arete Two, also filter fine particles.
Should I run a dehumidifier and air purifier together? You can, if you have both a moisture problem and want particle filtering. A combined unit saves floor space.
What you need
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Meaco Arete Two 20L: 38 dB and H13 HEPA filter