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How Often Should You Change Your Air Purifier Filter? (And What Happens If You Don’t)
Your air purifier is only as good as its filter. Once a filter clogs, less air gets through and less gets cleaned, even though the fan is still running. Here’s how filters wear out, what makes them wear out faster, and how to tell when yours is due.
The quick answer
There’s no single lifespan that fits every home. How long a filter lasts depends on how often you run your purifier and what’s in your air. A filter in a pet-free bedroom used at night will last far longer than one running all day in a living room during haze season.
The simple rule: check your filters regularly, and replace them when the signs below show up. Otherwise, all of PRISM+'s Air Purifiers come with indicator lights on when to change the filter.
| Filter | What it does | How you know it’s due |
|---|---|---|
| Pre-filter | Catches hair, lint and larger dust | It looks visibly coated or blocked. |
| HEPA filter | Traps fine particles, including haze PM2.5 | Airflow drops, the fan works harder, or the filter has turned dark grey. |
| Activated carbon filter | Absorbs odours and some gases | Smells linger in the room even with the purifier running. |
Why filters wear out
A filter cleans air by catching particles as the fan pulls air through it. Everything it catches stays there. Over time the filter fills up, air struggles to pass through, and your purifier moves less clean air into the room.
Each filter type wears out in its own way:
- Pre-filter: gets coated in hair and dust. Once it’s blocked, it chokes airflow to everything behind it.
- HEPA filter: fills with fine particles you can’t see. It can’t be cleaned out, so once it’s loaded, it’s done. New to how HEPA works? Read “What Is a HEPA Filter And Does the Grade Actually Matter?”
- Carbon filter: soaks up odour molecules until its surface is full. After that, smells pass straight through. It can look fine and still be used up. Learn more in “Activated Carbon Filter vs HEPA: What’s the Difference?”
What shortens filter life
- Hours of use: a purifier running all day uses up its filter much faster than one switched on only in the evening.
- Haze days: outdoor PM2.5 can climb sharply during haze, and your filter catches much more per hour.
- Pets: hair clogs the pre-filter fast, and dander loads the HEPA filter.
- Cooking: smoke and grease particles load the HEPA filter, and cooking smells use up the carbon.
- Open windows: your purifier ends up cleaning outdoor air too, including road dust and construction dust.
- A room that’s too big: the purifier runs on high for longer to keep up. If that sounds like your setup, browse our Air Purifiers to find one sized for your space.
Signs your filter is due
- Your purifier’s filter reminder comes on.
- Airflow feels weaker than it used to.
- The fan sounds louder, or it runs on high more often.
- You notice a musty or stale smell when it’s running.
- The pre-filter is visibly coated, or the HEPA filter has turned dark grey.
Colour alone isn’t a reliable guide. A carbon filter is dark from day one, and a HEPA filter can be heavily loaded with fine particles before it looks dirty.
What happens if you wait
- Weaker cleaning: less air gets through the filter, so the room gets cleaned fewer times an hour. During haze, indoor PM2.5 stays high for longer, which is exactly when you need the purifier most.
- A noisier fan: the fan works harder to push air through a clogged filter.
- A musty smell: in Singapore’s humidity, an overloaded filter can start to smell. A used-up carbon filter also stops removing cooking and pet odours.
How to replace it
Swapping a filter only takes a few minutes. Follow the steps in this video:
Where to buy replacement filters
Get genuine PRISM+ filters from our website here. Tip: keep a spare at home, so you’re not waiting on a delivery when the air turns bad.
Shopping for your first purifier, or one for another room? See our Air Purifiers.
FAQ
Can I wash my filter instead of replacing it? Not the HEPA or carbon filter. Water damages HEPA fibres, a damp filter can grow mould, and washing doesn’t restore carbon. Some pre-filters can be cleaned, so check your user manual.
Should I change my filter early after a bad haze? Not automatically, but check it. If your purifier ran on high for days during a long haze spell, the filter may be due sooner than usual. Look for the signs above, and replace it if they show.
Do spare filters expire? Keep spares sealed in their original packaging, somewhere cool and dry. Don’t unwrap a filter until you’re ready to fit it, because carbon starts absorbing household odours once it’s exposed.
Will my filter fit my other purifier? Filters are made for specific models.