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Guide
How often should you actually change a HEPA filter?
Every box says a number, but the honest answer is "it depends on your air." Here's what actually moves the replacement window, and the cheap tells that beat the calendar.
The real drivers
- True HEPA layer — typically 6–12 months. It clogs with fine particles; you can't wash it back.
- Activated carbon — 3–6 months. It saturates with odor/VOCs faster than the HEPA clogs, which is why combo units list two numbers.
- Pre-filter — often washable; rinse monthly and it extends the HEPA's life.
Tells it's spent
Grey/brown across the whole pleats (not just the intake side), a musty smell when the fan runs, or the unit ramping to high speed on "auto" in clean air. Pets, wildfire season, and new-build dust all shorten the window.
The trap
A clogged filter doesn't stop the fan — it just stops filtering while you keep paying for electricity. That's the case for a reminder: the failure is invisible.
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FAQ
Can you wash and reuse a HEPA filter?
No — washing a True HEPA layer damages the fibers and it won't filter the same. You can rinse a separate washable pre-filter, but the HEPA is a replace-only part.
Does running the purifier 24/7 mean changing filters more often?
Yes, roughly proportionally. Continuous use in dusty or pet homes can halve the window versus a few hours a day in clean air.