Before you buy a purifier for your child’s room, learn what HEPA, CADR and ACH actually promise, and which advertised features to skip.
What to remember
- A true HEPA filter captures at least 99.97% of particles at 0.3 microns, and particles larger or smaller are trapped even more efficiently.
- Size a purifier with the two-thirds rule: a smoke CADR at least two-thirds of the room’s square footage, or equal to it for wildfire smoke.
- The EPA recommends models that provide at least 4.8 air changes per hour for their recommended room size.
- Never buy a purifier that intentionally generates ozone, a lung irritant; CARB certifies devices that meet its ozone limit of 0.050 ppm (50 ppb).
- Expect to replace the filter at least once a year with genuine filters, since non-genuine ones can capture fewer particles and void the warranty.
Air purifier listings throw a lot of alphabet at you: HEPA, CADR, ACH, MERV, ppb. Those letters carry real weight, because the EPA says levels of certain pollutants are often two to five times higher indoors than outdoors, and most of us spend about 90 percent of our time inside. They matter even more for families with kids, because the EPA warns against one advertised feature, ozone generation, that irritates the lungs. This glossary explains what each term guarantees, what it does not, and how to stack two models up against each other.
HEPA: What the Term Guarantees and What It Does Not
HEPA filter. Short for “high efficiency particulate air,” a term officially defined by the U.S. Department of Energy. A HEPA filter is a pleated mechanical filter that can theoretically capture at least 99.97% of airborne particles at a size of 0.3 microns, including dust, pollen, mold and bacteria.
Mechanical filter. A filter that physically traps particles in a dense mat of fibers, usually fiberglass, rather than relying on electrical charge. This is the type of filtration behind the HEPA label.
MPPS (most penetrating particle size). The particle size that is hardest to capture, which the Department of Energy standard pegs at 0.3 microns. Particles larger or smaller than that are trapped with even higher efficiency, so the 99.97% figure describes a worst case, not a best case.
“HEPA-type” or “HEPA-like.” Marketing shorthand for filters that do not claim to meet the Department of Energy’s HEPA standard. If a product does not clearly state it uses a true HEPA filter, treat the label as unverified.
What HEPA does not cover. A HEPA filter targets particles, not gases such as volatile organic compounds. The EPA also cautions that no air cleaner or filter removes every pollutant from your home.
CADR: Matching the Number to Your Room Size
CADR (Clean Air Delivery Rate). A rating system from the Association of Home Appliance Manufacturers (AHAM) that measures how fast an air cleaner filters three particle types: dust, pollen and tobacco smoke. Higher numbers mean faster cleaning and a larger room the unit can handle.
Two-thirds rule. AHAM’s rule of thumb for sizing: choose a smoke CADR at least two-thirds of the room’s area in square feet. A 200-square-foot room, for example, calls for a smoke CADR of at least 132.
Smoke CADR. The CADR figure to prioritize, especially for a child’s bedroom or for wildfire smoke, since smoke particles are small. AHAM recommends that when you are filtering wildfire smoke, you pick a model with a smoke CADR equal to the room’s size in square feet.
CFM (cubic feet per minute). The unit CADR is reported in. Harvard’s Portable Air Cleaner Sizing Tool advises that when a manufacturer lists several CADR numbers, you use the one for dust.
AHAM Verifide. A seal, usually found on the packaging, showing that an independent laboratory tested the unit and verified its CADR and suggested room size.
Air Changes per Hour and Why It Matters for Kids’ Rooms
ACH (air changes per hour). How many times per hour the air in a room gets cleaned, factoring in the air cleaner and the room’s normal ventilation. The EPA recommends looking for models that provide at least 4.8 ACH for their recommended room size.
Suggested room size. The square footage the manufacturer says the unit can handle, typically printed on the packaging, label or website listing. It only holds up if the CADR behind it is real, which is one more reason to look for the Verifide seal.
PM2.5 and PM10. Shorthand for fine and coarse particulate matter, two common indoor contaminants. Smoke, cooking and dust generate these particles, and a true HEPA filter with a properly sized CADR is how a purifier goes after them.
Ozone, Ionizers and Terms to Be Wary Of
Safety alert: The EPA says never buy or use an air cleaner that intentionally generates ozone, a lung irritant. Also skip any device that does not meet state regulations or industry standards for ozone emissions.
Ozone. A gas that irritates the lungs. Some devices produce it deliberately and sell it as a cleaning method, and the EPA’s guidance is blunt: do not use ozone generators in occupied spaces.
Ionizer. An electronic air cleaner that releases charged ions to make particles clump and settle. CARB, the California Air Resources Board, groups ionizers with electronic devices that may generate ozone but have been tested to stay at or below its limit.
Electrostatic precipitator, PCO and hydroxyl generator. Other electronic cleaning technologies in CARB’s “electronic” category, which also includes devices with UV light components. Electronic designs can produce ozone; mechanical filters do not.
CARB certification. California has required certification of portable indoor air cleaning devices sold there since 2010. Electronic air cleaners must be tested for ozone emissions and meet a limit of 0.050 parts per million, or 50 ppb. CARB publishes a list of certified devices and cautions that certification measures ozone output, not cleaning effectiveness.
ppb (parts per billion). The concentration unit behind the CARB ozone limit: 0.050 ppm works out to 50 ppb.
Filter Types, Replacement Costs and Labels
Pre-filter. A first-stage filter that traps larger particles like lint and pet hair before air reaches the main filter. Many models combine the two in one unit.
Activated carbon filter. A second filter, often paired with HEPA, that helps reduce odors, including smoke smells from tobacco or wildfires. This is the layer aimed at gases rather than particles.
MERV. A rating used to compare furnace and central HVAC filters, the whole-home counterparts to a portable purifier. It is the number to check if you are upgrading the filter in your heating and cooling system instead of, or in addition to, buying a room unit.
Genuine replacement filter. The filter made by the purifier’s own manufacturer. Lookalike filters may fit poorly, use thinner materials, capture fewer particles, or shed fibers and clog the unit. A non-genuine filter can even void the manufacturer’s warranty, so it helps to understand how full and limited warranties work before you shop for replacements.
Replacement schedule. Most portable purifiers need a fresh filter about every 6 to 12 months, and most households should expect to replace the filter at least once a year. Heavy smoke, lots of pet dander or dusty air shorten that span, so check the manual. If the model you choose ever turns up in a safety recall, follow what to do when something you own is recalled.
Using These Terms to Compare Two Models
Put the two boxes side by side and work down this list:
- Room fit. Each unit’s suggested room size should meet or beat the square footage of the room it will live in, likely a bedroom or the living room, where the EPA suggests placing purifiers you run most.
- CADR. A higher smoke CADR means faster cleaning, but do not just buy the biggest number on the shelf. A unit that is too large for the room adds unnecessary noise and energy use, and one that is too small will fall short.
- Filtration type. True HEPA, plus an activated carbon filter if odors or gases are a concern.
- Ozone. No intentional ozone generation, and ideally CARB certification even if you do not live in California.
- Long-term cost. Check the price and availability of the replacement filter before checkout, since you will be buying it at least yearly.
| Term | What to check on the label |
|---|---|
| HEPA | States a true HEPA filter, not “HEPA-type” |
| CADR | Smoke CADR at least two-thirds of the room’s square footage |
| ACH | At least 4.8 air changes per hour for the recommended room size |
| Ozone | No intentional ozone; CARB certification for electronic models |
| AHAM Verifide | Seal present, confirming independent lab testing |
One last detail that is not printed on the box: the EPA advises running your purifier at a higher speed and for longer stretches to get the most out of it. A purifier that is properly sized for the room is also the best way to keep noise reasonable, which matters in a room where a child is trying to sleep. And remember that filtration is a supplement to, not a substitute for, removing pollution sources at home and ventilating with clean outdoor air.
Parents also ask
What CADR do I need for a 200-square-foot room?
At least 132 for smoke under AHAM’s two-thirds rule, which is two-thirds of the room’s square footage. If wildfire smoke is your main concern, look for a smoke CADR of 200, equal to the room size.
Are ionizers safe to use around kids?
Ionizers fall into CARB’s electronic category because they may generate ozone. Choose a CARB-certified device that has been tested to emit no more than 0.050 parts per million, or pick a mechanical HEPA unit instead.
How often should I replace the filter?
About every 6 to 12 months depending on use and air quality, and at least once a year for most households. Heavy smoke, pet dander or dust can shorten that span.
Does HEPA filtration remove gases and odors?
No, HEPA filters target particles. A separate activated carbon filter helps reduce odors, including smoke smells from tobacco or wildfires.
This guide is general information for U.S. shoppers, not legal advice. Safety rules and store policies change, so follow the product’s instructions and labels and check official sources such as CPSC.gov, NHTSA.gov and FTC.gov.