"HEPA" is one of the few air-filter terms with a real definition behind it. The labels around it, from "HEPA-type" to "H13", mean less or something different, and knowing which is which saves you from paying for a word.
A true HEPA filter removes at least 99.97% of airborne particles 0.3 microns in size, the U.S. Department of Energy's definition as cited by the EPA. H13 and H14 are classes from the European standard EN 1822, capturing at least 99.95% and 99.995% at each filter's most penetrating particle size; for a home air purifier, a true HEPA or H13 filter is enough, and airflow matters more than the class.
What makes a filter HEPA
HEPA stands for high-efficiency particulate air. The EPA describes it as a pleated mechanical filter that can remove at least 99.97% of dust, pollen, mold, bacteria and other airborne particles 0.3 microns in size. A filter that meets that test can be called HEPA; one that merely resembles it cannot.
Why 0.3 microns
A filter doesn't work like a sieve. Mechanical filters catch particles by three effects at once, and each one favors a different size.
Impaction catches the largest particles: they carry too much momentum to follow the air as it bends around a fiber, so they hit it head-on. Interception catches mid-size particles that follow the airflow but graze a fiber closely enough to stick. Diffusion catches the smallest particles, which get jostled by air molecules into a random path that drifts them into fibers.
Impaction and interception weaken as particles shrink, while diffusion only takes hold once particles are very small. Near 0.3 microns all three are at their weakest at the same time, so that size slips through most easily. A filter that still stops 99.97% of 0.3-micron particles stops an even higher share of everything larger and smaller, which is why the standard tests exactly there.
What size are the particles a HEPA filter catches
ASHRAE Standard 52.2, the standard that defines home HVAC filter ratings, sorts airborne particles into three size bands and names what tends to fall in each. The smallest band bottoms out near the 0.3-micron HEPA test point.
| Particle size | Common examples |
|---|---|
| 3.0–10 microns | Pollen, dust mite debris, larger dust |
| 1.0–3.0 microns | Mold spores, fine dust |
| 0.3–1.0 microns | Bacteria, smoke, virus-carrying particles |
A true HEPA filter is tested at 0.3 microns, the bottom of that smallest band, so it clears the particles in every row above its test point with room to spare. Some individual particles are smaller than 0.3 microns, but diffusion catches those at an even higher rate than the test size. For the same size bands applied to furnace filters, see the MERV rating chart.
H11, H13 and H14
These labels come from the European standard EN 1822, which rates filters at their most penetrating particle size:
| Class | Minimum efficiency at the most penetrating particle size |
|---|---|
| E11 (older editions: H11) | 95% |
| E12 (older editions: H12) | 99.5% |
| H13 | 99.95% |
| H14 | 99.995% |
H11 and H12 were renamed E11 and E12 in later editions, so a filter sold as "H11" meets the lower, 95% class, not HEPA. H14 matters in cleanrooms and hospitals; in a home, the difference between H13 and H14 is far smaller than the difference good airflow and proper sizing make.
"HEPA-type" and "HEPA-like"
These terms have no standard behind them. A "HEPA-type" filter can capture far less than 99.97% of fine particles. Look for "true HEPA" with a stated efficiency at 0.3 microns, or an EN 1822 class of H13 or higher.
Airflow matters as much as the filter
A perfect filter cleans only the air that passes through it. For an air purifier, the clean air delivery rate (CADR) combines filter efficiency and airflow, and it's the number to compare between models; see our air purifier sizing guide. The EPA recommends choosing an air cleaner sized for the room you use it in.
HEPA versus MERV in a home system
Home furnaces rate their filters on the MERV scale, not the HEPA standard, and the two don't line up one-to-one. The MERV scale used for home filters runs from 1 to 16 under ASHRAE Standard 52.2; true HEPA is a separate standard that sits above the top of that scale.
| Filter | Capture of 0.3–1.0 micron particles | Typical use |
|---|---|---|
| MERV 8 | Not rated at this size | Standard furnace filter |
| MERV 13 | At least 50% | Highest common home furnace level |
| MERV 16 | 95% | Hospitals, clean rooms |
| True HEPA | 99.97% at 0.3 microns | Portable purifiers, whole-house HEPA with its own fan |
Most home air handlers can't pull enough air through a true HEPA filter, which is dense and chokes airflow. That's why central systems stop at MERV; the EPA notes that MERV 7 to 13 filters are nearly as effective as true HEPA for most airborne indoor particles. For the full scale and the airflow trade-off, see the MERV rating chart.
Replacing a HEPA filter
HEPA media is a dense mat of fine fibers, and that structure is what earns the rating. Washing or vacuuming a filter that isn't labeled washable tears and flattens those fibers, opening gaps that let particles through, so a cleaned HEPA filter no longer meets its rating.
Replace a disposable HEPA filter on the maker's schedule rather than trying to clean it. A loaded filter also restricts airflow, so a purifier moving less air cleans less of the room even when the media still rates HEPA.
Frequently asked questions
What does a HEPA filter remove?
At least 99.97% of airborne particles 0.3 microns in size, including dust, pollen, mold spores and bacteria, and even more of larger and smaller particles. It doesn't remove gases or odors; that takes activated carbon.
Is H13 better than true HEPA?
They're close. H13 requires at least 99.95% at the most penetrating particle size under EN 1822; true HEPA requires 99.97% at 0.3 microns under the U.S. definition. Either is enough for a home.
Is H14 worth it for a home air purifier?
Rarely. The gain over H13 is tiny next to the effect of airflow and room size.
Can I put a HEPA filter in my furnace?
Usually not. Most home systems can't move enough air through one; a high-MERV filter the system can handle is the practical choice.
Does a HEPA filter remove viruses and COVID?
It removes the particles that carry them. HEPA captures 99.97% of 0.3-micron particles and a higher share above and below that size, and virus-carrying droplets and nuclei fall largely in the 0.3 to 1.0 micron band that HEPA targets. Individual virus particles smaller than 0.3 microns are caught efficiently by diffusion, though a filter only cleans the air that actually passes through it.
Does a HEPA filter remove smoke or VOCs?
It removes the solid and liquid particles in smoke, which sit largely in the 0.3 to 1.0 micron range, but not the gases. Smoke also carries volatile organic compounds and odor molecules, and those are gases that pass straight through HEPA media. Removing gases and odors takes activated carbon, a separate filter stage.
How long does a HEPA filter last?
It depends on how dirty your air is and how much the purifier runs, so follow the maker's replacement interval for your model. Do not wash or vacuum a filter unless it's labeled washable; cleaning non-washable HEPA media damages the fibers and drops it below its rating. A loaded filter also restricts airflow and cleans less, so change it sooner if airflow drops or the purifier gets louder.