Air purifier sizing Last reviewed June 2026
What Size Air Purifier Do You Need for Allergies?
By the WhatSize editorial team 4 min read Standards-reviewed
For allergy relief, your air purifier should achieve 4.8 air changes per hour (ACH) — meaning the entire rooms air is filtered nearly 5 times per hour. Use the formula: Required CADR = (Room sq ft x 8) x 4.8 / 60.
The 4.8 ACH Standard for Allergy Sufferers
The Asthma and Allergy Foundation of America recommends 4.8 air changes per hour (ACH) for allergy relief. This is higher than the typical 4 ACH recommended by AHAM because allergy sufferers benefit from more frequent filtration cycles to continuously remove allergens from the air.
At 4.8 ACH, the air in your room is completely filtered about every 12.5 minutes. This rapid turnover is critical during allergy season when pollen counts spike and windows may be open occasionally.
Top picks for this size
These Amazon-available picks meet the calculated spec. For region-specific or licensed contractor-installed options, consult a local professional. See our Disclaimers.
CADR Requirements by Room for Allergy Relief
- Small bedroom (150 sq ft): Smoke CADR 96+ — a 100 CADR unit handles this well
- Standard bedroom (250 sq ft): Smoke CADR 160+
- Living room (400 sq ft): Smoke CADR 256+ — you are looking at top-tier units
- Open floor plan (600+ sq ft): Smoke CADR 384+ — consider two units or a whole-house system
Frequently asked questions
What size air purifier helps with allergies?
True HEPA (High Efficiency Particulate Air) is the gold standard, capturing 99.97% of particles at 0.3 microns. Most allergy triggers (pollen, dust mites, mold spores) are 2-100 microns, well within HEPAs range.
Should I run my air purifier 24/7 for allergies?
Yes, especially during allergy season. Allergens continuously enter your home through open doors, on clothing, and via ventilation. Continuous operation at a medium setting is better than high-speed intermittent use.
Can an air purifier replace allergy medication?
No. An air purifier reduces airborne allergens, which can reduce symptoms and medication needs, but it is not a replacement for prescribed allergy treatment. It works best as part of a comprehensive allergy management plan alongside medication, dust-mite-proof bedding, and regular cleaning.
You might also need
More air purifier sizing guides
- What Size Air Purifier for a Bedroom? CADR Guide
- What Size Air Purifier for a Large Room (500+ Sq Ft)?
- What Size Air Purifier for a Living Room?
- What Size Air Purifier Do Pet Owners Need?
- How Many Air Changes per Hour Do I Need? (ACH Chart)
- What Is CADR? Air Purifier Sizing Explained
- What Size Air Purifier for Smoke and Wildfire? CADR Guide