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CADR, short for Clean Air Delivery Rate, is the number that tells you how quickly a purifier removes particles from the air. It comes from AHAM test procedures and is reported in cubic feet per minute for three particle types: smoke, dust and pollen.
If you only look at one number on a purifier box, it should be CADR. This guide explains what CADR means, how to use it to size a room, where marketing claims can mislead and what to check besides CADR. Choices come from our affiliate table; we rely on AHAM and EPA information, not our own testing.
CADR helps you if
- You are comparing units of different brands
- You want to size a unit for a specific room
- You want to cut through coverage claims
CADR is not enough if
- You ignore filter type and cost
- You skip noise checks
- You need odor or gas removal
Key Takeaways
- CADR measures how fast a purifier cleans smoke, dust and pollen-sized particles.
- Use the smoke CADR as your guide for sizing: about two-thirds of the floor area for 8 foot ceilings.
- Higher CADR means faster cleaning but often more noise and cost.
- Beware of coverage claims without a stated CADR.
- CADR says nothing about filter cost, odor control or ozone.
- Taller ceilings and open layouts need more CADR.
- Avoid ozone and ionizer modes, which the EPA advises against.
Choosing Beyond CADR: A Short Checklist
- True HEPA filter, not HEPA-type
- Noise level at the speed you will run
- Filter replacement cost and schedule
- Warranty length and support
- Power use at medium speed
- Carbon amount if odors matter
- No ozone or ionizer mode you cannot disable
Treat this list as the second stage of your search once you have identified models with the right CADR.
Common Mistakes When Reading CADR
The first mistake is comparing CADR numbers from different types of particles. A pollen CADR of 300 is not equivalent to a smoke CADR of 300. The second is ignoring room height. The third is trusting a CADR for a different model in the same family. The fourth is assuming that the highest speed is how you will run the unit. If you plan to run on low, find a CADR or airflow figure for low, or accept that real-world cleaning will be slower.
The fifth mistake is buying much more CADR than you need. A very powerful unit in a small room may be louder and more costly with no extra benefit. Aim for the target with a modest margin.
A Quick Reference for Common Rooms
Use the two-thirds rule as a starting point: 120 square feet needs about 80, 200 square feet needs about 135, 300 square feet needs about 200 and 500 square feet needs about 330. Add margin for taller ceilings, open layouts, pets, smoke or sensitive users.
How CADR Interacts With Filter Aging
As a filter loads with particles, airflow can drop, and the real-world CADR falls below the tested figure. A clean pre-filter and a fresh HEPA filter keep performance near the rated value. Plan to inspect the pre-filter every few weeks and replace the main filter on schedule. If you notice weaker airflow at the exhaust or longer smell recovery after cooking, check the filters before you assume the unit is too small.
Some units show a filter-life indicator based on running hours rather than actual loading. In a smoky or dusty home, change the filter earlier than the indicator suggests.
Top Picks: Air Purifiers With Published Performance
These options come from our affiliate table. Check the listing for the current CADR, filter type and replacement cost.
Using CADR to Size a Room
AHAM suggests that the smoke CADR should be at least two-thirds of the room area in square feet for 8 foot ceilings. A 300 square foot room points to a CADR near 200. Taller ceilings need more.
Spotting Misleading Claims
Beware of area claims with no CADR, or CADR numbers with no source. Some listings use a peak or an unusual test condition. If you cannot find a CADR, assume the unit is weaker than the headline suggests.
What CADR Does Not Tell You
CADR says nothing about noise, filter cost, ozone emissions or odor control. A powerful unit can be loud, and a high CADR with a thin filter can be costly to maintain. Treat CADR as the first filter in your decision, not the only one.
What CADR Measures
CADR is the volume of clean air a purifier delivers per minute for a given particle size range. A unit with a smoke CADR of 300 cleans the equivalent of 300 cubic feet of air per minute of smoke-sized particles. Higher numbers mean faster cleaning.
The AHAM test uses a standard test chamber and standard particles, which makes it a fair comparison between models.
Smoke, Dust and Pollen: The Three Numbers
Smoke represents the smallest particles, dust the middle range and pollen the largest. Smoke CADR is usually the lowest and the most telling about fine-particle performance. If a listing reports only one CADR, check which particle type it refers to.
| Particle type | Size range | Examples |
|---|---|---|
| Smoke | 0.09 to 1.0 microns | Smoke, fine combustion particles |
| Dust | 0.5 to 3 microns | House dust, some dander |
| Pollen | 5 to 11 microns | Pollen, large particles |
A Worked Example: Comparing Two Units for a 300 Square Foot Room
Unit A lists a smoke CADR of 200, dust 210 and pollen 220 and costs $180 with a $40 filter every year. Unit B lists a smoke CADR of 120 and a headline claim of 400 square feet at one air change per hour, and costs $120 with a $30 filter every six months. Unit A matches the two-thirds rule for a 300 square foot room; Unit B does not. Over two years, Unit A costs about $260 in total, while Unit B costs about $240 plus an undersized fan. The cheaper unit is not a bargain if it cannot clean the room.
| Item | Unit A | Unit B |
|---|---|---|
| Smoke CADR | 200 | 120 |
| Meets 300 sq ft target | Yes | No |
| Filter cost per year | $40 | $60 |
| Two-year cost | About $260 | About $300 |
Air Changes Per Hour
Another way to read CADR is through air changes per hour, the number of times a room’s air passes through the purifier each hour. The two-thirds guideline gives about 4.8 air changes per hour for 8 foot ceilings. Fewer changes mean slower cleaning; more changes mean faster cleaning, within the limits of noise and comfort.
Why Real Rooms Perform Below Lab Results
Test chambers are sealed and simple. Real rooms have furniture, open doors and drafts, and the pollution source keeps producing. Expect lower performance than the number suggests and add a margin of 20 to 30 percent where you can.
CADR and Noise Trade-Offs
A high CADR often comes from a bigger fan. Larger fans can be quieter at a given airflow, but top speed is usually loud. Look at the CADR at the speed you will actually use. Some makers publish CADR only for the highest speed, which tells you little about nightly performance.
CADR Versus Filter Quality
A strong fan with a weak filter is not a good purifier. True HEPA matters because it captures very fine particles. The CADR test measures the whole system, so a good CADR already includes filter performance for the tested particle types, but it does not reflect long-term durability or cost.
How to Verify a CADR Claim
Look for the AHAM Verifide seal or a listing in the AHAM directory. Check that the CADR numbers refer to the model you are buying, since similar models can differ. If you cannot verify a figure, treat it as unconfirmed.
How to Choose
- Find the CADR for smoke, dust and pollen
- Match smoke CADR to your room using the two-thirds rule
- Check noise at the speed you will use
- Check filter type and replacement cost
- Avoid models with ozone or ionizer modes you cannot turn off
Do
- Match the unit’s rated coverage to your room first
- Run it consistently, not only when the air feels bad
- Leave space around the unit for airflow
- Replace filters on the maker’s schedule
Don’t
- Do not buy on looks or price alone
- Do not block the intake or exhaust
- Do not skip filter changes
- Do not expect a purifier to fix every source of pollution
Honest Limits
- This guide uses manufacturer information and public guidance from the EPA and AHAM, not our own lab tests.
- Features and room ratings change between model years, so confirm on the listing before you buy.
- A purifier is not a medical device and does not replace medical advice or treatment.
Who Should Skip This
Skip units that show coverage claims but no CADR.
Skip ionizer and ozone modes; the EPA advises against ozone-generating devices.
When to See a Professional
If you have asthma or allergies, talk to your doctor. CADR helps you size a unit but does not guarantee a health outcome.
If a unit produces a burning smell or overheats, unplug it and contact the maker.
Frequently Asked Questions
What is CADR?
Clean Air Delivery Rate is the volume of clean air a purifier delivers per minute for smoke, dust and pollen-sized particles.
What CADR do I need?
About two-thirds of the floor area for 8 foot ceilings, using the smoke CADR as the guide.
Is a higher CADR always better?
It cleans faster but may be louder and cost more. Match it to your room and noise tolerance.
What are the three CADR numbers?
Smoke, dust and pollen. Smoke represents the smallest particles and is usually the lowest.
Does CADR include filter quality?
The test measures the whole system on the tested particle types, but it does not reflect cost or long-term durability.
Can I trust coverage claims?
Only if backed by a CADR. Many claims assume slow air change rates.
What if a unit has no CADR?
Treat the performance as unverified and compare with units that publish CADR.
Does CADR matter for odors?
No. Odor control depends on the amount of carbon.
How do taller ceilings change CADR needs?
They increase air volume, so you need more CADR for the same air changes.
What is AHAM Verifide?
A program that verifies CADR claims through AHAM testing.
Bottom Line
CADR is the clearest way to compare how fast purifiers clean air. Use it to size a room, then check noise, filters and cost.
If a listing hides its CADR, treat that as a warning sign.
Related reading: bed,fan,lw
Sources: EPA, Guide to Air Cleaners in the Home; AHAM Verifide.