CADR and room size
CADR (clean air delivery rate) is how many cubic feet of clean air an air purifier delivers per minute, measured separately for smoke, dust and pollen, plus a PM2.5 figure. In DOE's certification records the effective room size is the smoke CADR times 1.55, AHAM's formula for 4.8 air changes an hour, so a 200 cfm smoke CADR covers about 310 sq ft (DOE data as of 2026-11-03).
Computed from 317 air cleaner records in the DOE Compliance Certification Database, as of 2026-11-03. Formula: AHAM, Portable Air Cleaners and Air Changes per Hour.
Key findings
- In 296 DOE air purifier records, the effective room size is the smoke CADR times 1.51 to 1.57, median 1.55 (DOE data as of 2026-11-03). That's AHAM's formula for 4.8 air changes an hour in a room with 8 ft ceilings.
- The median DOE certified air purifier has a smoke CADR of 140 cfm and an effective room size of 217 sq ft (as of 2026-11-03).
- 98 of 296 DOE certified air purifiers have an effective room size of 300 sq ft or more, and 30 reach 500 sq ft (as of 2026-11-03).
- All 296 air purifier records with values file an efficiency at or above DOE's tier 2 minimum, the level for units made since December 31, 2025. The median is 4.9 PM2.5 CADR per watt (as of 2026-11-03).
- The median DOE certified air purifier uses 184 kWh a year, about $33.41 at 18.16 cents/kWh, the US average for August 2026 (EIA). DOE data as of 2026-11-03.
Source: DOE Compliance Certification Database (air purifiers), data as of 2026-11-03.
Where does the room size figure come from?
AHAM's formula: room size in sq ft equals smoke CADR times 1.55. It assumes an 8 ft ceiling and is built so the purifier keeps up with unfiltered air coming into the room, removing 80% of smoke particles at steady state. Worked through, that's 4.84 air changes an hour, which AHAM rounds to 4.8 (AHAM white paper).
DOE's records follow it almost to the decimal. Across 296 filings with both figures, room size divided by smoke CADR runs from 1.51 to 1.57. Flip it over and you get the rule of thumb: smoke CADR should be about 65% of the room's floor area. 21 of the 317 air cleaner records list no CADR at all, and they're left out of every figure here.
What's the difference between smoke, dust and PM2.5 CADR?
DOE's test (10 CFR 430, appendix FF) measures smoke, dust and pollen CADR under AHAM AC-1-2020, and works out PM2.5 CADR under AHAM AC-7-2022. Smoke particles are the smallest, so smoke CADR is the strictest figure, and it's the one the room size uses. PM2.5 CADR is what DOE's efficiency figure (IEF, PM2.5 CADR per watt) and its product classes are built on.
Medians across DOE's records: 140 cfm smoke, 152 cfm dust and 147 cfm PM2.5.
How big a room do certified air purifiers really clean?
| Smoke CADR (cfm) | Models | Share | Median room | Median IEF | kWh/year | Per year |
|---|---|---|---|---|---|---|
| Under 100 | 93 | 31% | 84 sq ft | 3.5 | 88 | $15.98 |
| 100 to 149 | 71 | 24% | 202 sq ft | 4.7 | 167 | $30.33 |
| 150 to 199 | 38 | 13% | 255 sq ft | 4.65 | 226 | $40.95 |
| 200 to 299 | 52 | 18% | 377 sq ft | 5.55 | 273 | $49.58 |
| 300 or more | 42 | 14% | 549.5 sq ft | 5.8 | 390 | $70.73 |
Medians per row. kWh/year is the annual energy figure in each DOE record. Cost at 18.16 cents/kWh (US average residential price, August 2026), EIA Electric Power Monthly, table 5.6.A.
31% of certified purifiers deliver under 100 cfm of smoke CADR, which is a room of about 84 sq ft at the median. The highest smoke CADR on file is Dyson BP10-A at 591 cfm, an effective room size of 916 sq ft.
Why does the box claim a bigger room than DOE?
A bigger room figure means fewer air changes an hour. The math is simple: air changes an hour equal smoke CADR times 60, divided by the room's volume. For a 200 cfm smoke CADR in a room with 8 ft ceilings:
| Room | Air changes an hour |
|---|---|
| 310 sq ft | 4.8 |
| 500 sq ft | 3 |
| 1,000 sq ft | 1.5 |
| 1,500 sq ft | 1 |
So a 200 cfm unit "for 1,500 sq ft" is a claim of about 1 air change an hour, where AHAM and DOE's figure assume 4.8. Neither number is false. They answer different questions, and only DOE's is filed the same way for every model.
What size air purifier do I need?
Divide the room's square feet by 1.55 for the smoke CADR you need. For the common sizes, with the count of certified units whose DOE room size reaches it:
| Room | Smoke CADR needed | For wildfire smoke | Certified units that fit |
|---|---|---|---|
| 200 sq ft | 130 cfm | 200 cfm | 174 |
| 300 sq ft | 194 cfm | 300 cfm | 98 |
| 500 sq ft | 323 cfm | 500 cfm | 30 |
| 1,000 sq ft | 646 cfm | 1,000 cfm | 0 |
The wildfire column is AHAM's stricter advice. For wildfire smoke it changed the formula to room size equals smoke CADR, with no 1.55, which raises the purifier to about 7.5 air changes an hour and 86% removal (AHAM white paper).
How efficient are certified air purifiers?
| PM2.5 CADR (cfm) | Tier 1 minimum | Tier 2 minimum | Models | Median | Below tier 2 |
|---|---|---|---|---|---|
| 10 to 99 | 1.7 | 1.9 | 90 | 3.5 | 0 |
| 100 to 149 | 1.9 | 2.4 | 66 | 4.65 | 0 |
| 150 or more | 2 | 2.9 | 140 | 5.5 | 0 |
Minimums: 10 CFR 430.32(ee). Tier 1 applies to units made December 31, 2023 through December 30, 2025, tier 2 to units made on or after December 31, 2025.
Medians sit above the tier 2 floor in every class. The most efficient record on file is Blueair 4612522000 at 14 CADR per watt. The full ranking lists every unit by IEF.
Questions
What is a good CADR for an air purifier?
One whose smoke CADR covers your room: the room's square feet divided by 1.55. The median DOE certified smoke CADR is 140 cfm, enough for about 217 sq ft.
What size air purifier do I need for a 300 sq ft room?
A smoke CADR of about 194 cfm or more, which is a DOE effective room size of 300 sq ft. For wildfire smoke, AHAM's advice is 300 cfm. Models that qualify.
How much does it cost to run an air purifier all year?
DOE's records list annual energy in kWh. At the median of 184 kWh, that's $33.41 a year at 18.16 cents/kWh (US average residential price, August 2026). Bigger units use more: the median in the 300 cfm and up row is 390 kWh, $70.73 a year.
Are the same air purifiers sold under different brands?
57 of 317 DOE air cleaner basic models are filed under two or more brand names (as of 2026-11-03). Same unit clusters list them.
Will air purifiers stay under DOE rules?
In May 2025 DOE proposed withdrawing air cleaners as a covered product (Federal Register document 2025-08596, May 16, 2025). As of 2026-11-02 it was still a proposal. Figures already filed stay on this site with their dates.