They do different jobs. A dehumidifier removes water vapour. An air purifier filters particles and, with carbon, some smells. Neither does the other's job.
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Size my dehumidifierMatch the problem to the machine
| What you notice | Start with | Why |
|---|---|---|
| Wet windows, condensation on walls | Dehumidifier | It is a moisture problem. A purifier does not remove water vapour. |
| Laundry slow to dry indoors | Dehumidifier | Lower humidity speeds drying. |
| Musty smell in a damp room | Dehumidifier | The smell usually follows the damp. Fix the moisture first. |
| Dust, pollen, pet hair and dander | Air purifier | A filter traps airborne particles. |
| Smoke, wildfire haze, cooking particles | Air purifier | Look for a published smoke CADR and a good filter. |
| Cooking or pet smells | Air purifier with carbon | The activated carbon layer adsorbs odours. Amount varies a lot. |
| Visible mould growing on walls | Fix the cause first | A purifier may catch airborne spores but does not stop mould growing. A dehumidifier helps only if the cause is condensation. |
Where they overlap
Damp air and dust mites go together. An AO.com expert quoted by Ideal Home says humidity over 50% can encourage mould and dust mites. If allergies are the concern and the home is damp, lowering humidity and filtering the air can both help. Start with the one that matches the strongest symptom.
What to compare in each
- Dehumidifier: litres per day, the test conditions, type (compressor or desiccant), noise, running cost. See why ratings don't match real life and running costs.
- Air purifier: CADR for your room size, filter grade, filter replacement cost, noise. See room size and CADR.
Do you need both?
Sometimes, but rarely in the same room for the same reason. A damp rented flat with a pet might. Most people should solve the biggest problem first, live with it for a few weeks, and measure. A cheap hygrometer shows whether the dehumidifier is working.
Next
Condensation or drying laundry: use the dehumidifier sizer and see dehumidifiers compared. Dust, pollen or smoke: use the air purifier calculator and browse air purifiers.
Source: Ideal Home, What should the humidity be in a room?. The matching table is our summary. This is general information, not medical or building advice.