Sizing · reference
Air Purifier for a 100 Sq Ft Room: 65 CADR
EPA publishes a minimum clean air delivery rate of 65 cfm for a 100 square foot room, assuming an eight-foot ceiling.
Updated 30 Aug 2026
ReadSizing & CADR
The published minimum CADR for each room size, and the sizing mistakes that follow from ignoring it.
26 pages6 from the EPA table
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16 pagesSizing · reference
Air Purifier for a 200 Sq Ft Room: 130 CADR
EPA publishes a minimum clean air delivery rate of 130 cfm for a 200 square foot room, assuming an eight-foot ceiling.
Updated 30 Aug 2026
ReadSizing · reference
Air Purifier for a 300 Sq Ft Room: 195 CADR
EPA publishes a minimum clean air delivery rate of 195 cfm for a 300 square foot room, assuming an eight-foot ceiling.
Updated 30 Aug 2026
ReadSizing · reference
Air Purifier for a 400 Sq Ft Room: 260 CADR
EPA publishes a minimum clean air delivery rate of 260 cfm for a 400 square foot room, assuming an eight-foot ceiling.
Updated 30 Aug 2026
ReadSizing · reference
Air Purifier for a 500 Sq Ft Room: 325 CADR
EPA publishes a minimum clean air delivery rate of 325 cfm for a 500 square foot room, assuming an eight-foot ceiling.
Updated 30 Aug 2026
ReadSizing · reference
Air Purifier for a 600 Sq Ft Room: 390 CADR
EPA publishes a minimum clean air delivery rate of 390 cfm for a 600 square foot room, assuming an eight-foot ceiling.
Updated 30 Aug 2026
ReadSizing · reference
Why "Covers 1,500 sq ft" Means Very Little
Coverage claims are not standardised. The published minimum CADR is. See why the room-size row beats the box headline every time you compare.
Updated 30 Aug 2026
ReadSizing · reference
High Ceilings Change the Purifier You Need
Every published CADR assumes an eight-foot ceiling, so a taller room makes the table under-read. How much higher is not published.
Updated 30 Aug 2026
ReadSizing · reference
Two Small Air Purifiers or One Large One?
The minimums are published per room, so the floor plan decides this rather than total area. It is actually a floor-plan question.
Updated 30 Aug 2026
ReadSizing · reference
Five Air Purifier Sizing Mistakes
The five ways people end up with a unit that cannot do the job, and the published CADR row that would have prevented each mistake.
Updated 30 Aug 2026
ReadSizing · reference
Whole-House or Room Air Purifier?
One published minimum per room is why a single hallway unit does not cover a home. There is no published CADR for "the flat".
Updated 30 Aug 2026
ReadSizing · reference
What CADR Do I Need? Start With the Room
The whole method in one page: measure the room, read the published minimum, check the smoke rating. What follows is the whole method.
Updated 30 Aug 2026
ReadSizing · reference
Where to Put an Air Purifier in a Room
Clearance matters more than which corner you choose, because every published CADR assumes the air can actually reach the machine.
Updated 30 Aug 2026
ReadSizing · reference
Should You Run an Air Purifier All the Time?
Particles return the moment it stops, so the cost side is filter life and electricity. Sources keep generating, cooking, pets, bedding.
Updated 30 Aug 2026
ReadSizing · reference
Why an Oversized Air Purifier Is Quieter
A larger unit reaches the same CADR at a lower fan speed, the one good case for going above the minimum. Quiet is usually a sizing outcome, not a feature.
Updated 30 Aug 2026
ReadSizing · reference
Do Air Purifiers Actually Work?
They do one measurable thing well, and several advertised things without any published rating. So the honest answer is split.
Updated 30 Aug 2026
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10 pagesSizing · explainer
Air Purifier Not Helping Your Allergies? Likely Causes
Air purifier running but still sneezing? The likely causes, from an undersized unit to triggers no filter reaches, and what an air cleaner can honestly do.
Updated 25 Oct 2026
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Air Purifier Smells Bad or Musty? Causes and Fixes
Why an air purifier smells musty, burnt or stale, and how to fix it without a new machine: the filter chain causes, washing advice and when carbon helps.
Updated 25 Oct 2026
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Air Purifier Too Loud? Causes and How to Quiet It
A loud air purifier is usually undersized and running flat out, or has a small mechanical fault. The causes in order, most of them free to fix.
Updated 25 Oct 2026
ReadSizing · explainer
Air Purifier Blowing Dusty Air? Causes and Fixes
Dust coming out of an air purifier, or a room still dusty with one running? The likely causes, most of them cleaning or seating jobs, and when to stop.
Updated 25 Oct 2026
ReadSizing · explainer
Air Purifier Filter Light Won't Reset? Try This
Replaced the filter but the light won't reset? It is almost always the reset sequence, not a fault. What the light really measures and what to check.
Updated 25 Oct 2026
ReadSizing · explainer
Air Purifier Stopped Working? What to Check First
Air purifier won't turn on or stopped mid-run? The short diagnostic list, most of it outside the machine, plus two mistakes that make it worse.
Updated 25 Oct 2026
ReadSizing · explainer
Air Purifier Making a Rattling Noise? What to Check
A rattling air purifier usually has something loose, taped or stuck. The short list of causes for new and older units, and what to check with it unplugged.
Updated 25 Oct 2026
ReadSizing · explainer
Why Is My Air Purifier Blowing Cold Air? (It Is Normal)
An air purifier blowing cold air is almost always working as designed, because moving air feels cool. Why it happens, and the one real fault to check.
Updated 25 Oct 2026
ReadSizing · explainer
Air Purifier Using More Power? Likely Causes
A common complaint, and the handful of causes worth checking before replacing the unit. The electricity bill has opinions about your air.
Updated 25 Oct 2026
ReadSizing · explainer
Air Purifier Never Reaches Clean? 4 Likely Causes
Indicator never reaches clean? A mis-reading sensor, a room bigger than the rating, air leaking back in, or the meaning of clean. How to check all four.
Updated 25 Oct 2026
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