Air Purifier Buying Guide 2025
CADR, HEPA, and What Actually Matters

Air purifier marketing is full of meaningless numbers. "Covers rooms up to 1,500 sq ft." "5-stage filtration." "Ionizer technology." Most of it is designed to confuse you into spending more. Here is what actually determines whether an air purifier cleans your air.

1. CADR: The Only Number That Matters

CADR (Clean Air Delivery Rate) measures how fast a purifier cleans the air, in cubic feet per minute (CFM). It is independently tested and cannot be faked. Every air purifier worth buying publishes its CADR for smoke, dust, and pollen.

How to use CADR: Take your room's square footage and multiply by 0.67. That is the minimum CADR you need. A 300 sq ft bedroom needs at least 200 CFM. A 600 sq ft living room needs 400 CFM.

Ignore "covers up to X sq ft" claims. These are calculated at the lowest fan speed with 1 air change per hour — conditions you will never use. CADR is the honest number.

2. True HEPA vs. Everything Else

True HEPA captures 99.97% of particles at 0.3 microns — the most penetrating particle size. "HEPA-type" and "HEPA-like" have no legal definition. They are marketing terms for lower-grade filters. If a purifier does not explicitly say "True HEPA," assume it is not.

For allergy and asthma sufferers, True HEPA is essential. For general dust and odor reduction, HEPA-type is adequate. All our recommended purifiers use True HEPA.

3. The Filter Cost Trap

Air purifiers are not a one-time purchase. Filter replacements are the real cost. Here is the math over 5 years:

Purifier	Buy Price	Filters (5yr)	Total
Levoit Core 600S	$299	$250	$549
Coway Airmega 250	$399	$400	$799
Blueair 211+	$319	$600	$919
Winix 5500-2	$189	$200	$389

The Winix 5500-2 costs $189 upfront — but over 5 years, it is the cheapest by a wide margin because filters are only $40/year. The Blueair 211+ costs more over 5 years than purifiers that cost twice as much upfront, because its proprietary filters are $60 every 6 months. Always check filter cost before buying.

4. Carbon Filters: Activated Pellets vs. Coated Sheets

Carbon filters remove odors, cooking smells, and VOCs. There are two types:

• Activated carbon pellets: Looks like small black beads. Actually absorbs odors and chemicals. Found on premium purifiers like Coway and Winix.
• Carbon-coated sheet: A thin fabric with carbon powder sprayed on. Looks good on a spec sheet. Does almost nothing in practice. Found on most budget purifiers.

If you want to remove cooking smells or smoke, get a purifier with pellet-based carbon. If you only care about dust and pollen, the carbon filter type does not matter.

5. Room Size Reality Check

Room Size	Min CADR	Example	Our Pick
150 sq ft (bedroom)	100 CFM	Small bedroom, office	Winix 5500-2 ($189)
300 sq ft (master)	200 CFM	Master bedroom, living room	Levoit Core 600S ($299)
600+ sq ft (open plan)	400+ CFM	Open living/kitchen	Coway Airmega 250 ($399)

If your room is between two sizes, get the larger purifier and run it on a lower speed. It will be quieter and clean the air just as effectively.

6. Features Worth Paying For

• Auto mode with air quality sensor: Worth it. The purifier ramps up when it detects pollution and goes quiet when the air is clean. Saves energy and noise.
• Sleep mode: Worth it for bedrooms. Drops fan speed to near-silent and turns off display lights.
• WiFi/app control: Nice to have, not essential. Useful for scheduling (auto-on before bedtime) and checking filter life.
• Washable pre-filter: Very worth it. Catches pet hair and visible dust before it clogs the expensive HEPA filter. Coway's washable pre-filter is the best in the industry.
• Ionizer: Skip it. Some produce ozone. The Winix 5500-2 has one but lets you turn it off.