Air purifier boxes are full of room-size claims, filter buzzwords and big numbers. Three things actually decide whether you get your money's worth: a smoke CADR that matches your room, a filter that does what it says, and running costs you can live with for years. This guide uses the rules published by AHAM, the EPA, ENERGY STAR and the California Air Resources Board, plus a worked cost example, so you can compare any two models on paper.
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Short answer. Pick a unit whose AHAM-verified smoke CADR is at least two-thirds of your room's square footage (more for high ceilings or wildfire smoke), with a true HEPA filter for particles and a thick activated carbon filter if you need odor control. Avoid anything that makes ozone. Then add electricity and filters: a 77 W unit run all day at the August 2026 U.S. average of 18.16 cents/kWh costs about $122 a year in power alone, so five-year running costs can dwarf the sticker price.
This guide is research based. The Review NYU did not test any air purifier, measure any airflow or read any electricity meter. We read the rules and definitions that the industry and regulators publish, then did the arithmetic ourselves with the assumptions written out so you can swap in your own numbers.
On 13 November 2026 we read: the EPA's Guide to Air Cleaners in the Home, its page on what a HEPA filter is and its warning on ozone generators sold as air cleaners; AHAM Verifide's air filtration standards page and its white paper on air changes per hour; ENERGY STAR's room air cleaner page; the California Air Resources Board's air cleaner program page and consumer fact sheet; and the U.S. Energy Information Administration's Electricity Monthly Update. For a real-world cost example we used one widely sold model, the Coway Airmega Mighty AP-1512HH, because its maker lists wattage, CADR and filter prices on its own pages. That is an illustration, not a recommendation.
Clean Air Delivery Rate (CADR) is the industry's standard measure of how fast a portable air cleaner removes particles. AHAM, the appliance trade group that runs the Verifide certification, gives three CADR scores in cubic feet per minute: one each for tobacco smoke, dust and pollen (AHAM Verifide, read 13 November 2026). CARB describes CADR as airflow multiplied by the share of particles removed, so a loud fan pushing air through a weak filter does not get a high score (CARB).
Use the smoke number. The EPA says smoke, dust and pollen stand in for small, medium and large particles, and that the smoke CADR is the one to check if you care about the fine particles (PM2.5) of greatest health concern (EPA). Smoke is usually the lowest of the three numbers, which is why some marketing leads with the dust or pollen score instead.
Look for the AHAM Verifide mark on the box, or search AHAM's directory, so the CADR came from a third-party certification program rather than the seller alone.
AHAM's rule of thumb: the smoke CADR should be at least two-thirds of the room's floor area in square feet. Its own example is a 10 by 12 foot room, 120 square feet, which needs a smoke CADR of at least 80 (AHAM Verifide, read 13 November 2026). The EPA and ENERGY STAR publish nearly the same chart: 65 cfm per 100 square feet, rising to 390 cfm for 600 square feet (EPA; ENERGY STAR).
Where the rule comes from: AHAM's white paper says suggested room sizes assume an 8-foot ceiling and about 4.8 air changes per hour, which works out to room size = smoke CADR x 1.55 (AHAM white paper). Flip it and you get CADR = room area / 1.55, which is roughly two-thirds.
| Room | 2/3 rule (AHAM) | EPA / ENERGY STAR chart | Wildfire smoke (AHAM) |
|---|---|---|---|
| 10 x 10 ft (100 sq ft) | 67 | 65 | 100 |
| 10 x 12 ft (120 sq ft) | 80 | 78 | 120 |
| 12 x 15 ft (180 sq ft) | 120 | 117 | 180 |
| 15 x 20 ft (300 sq ft) | 200 | 195 | 300 |
| 20 x 20 ft (400 sq ft) | 267 | 260 | 400 |
| 20 x 30 ft (600 sq ft) | 400 | 390 | 600 |
The EPA chart lists 100, 300, 400 and 600 square feet directly; the 120 and 180 square foot rows are our interpolation at 0.65 cfm per square foot. Small differences between columns are rounding, not disagreement.
Do not overbuy for a small room. CARB advises against an oversized unit because larger cleaners are usually louder and use more energy, and ENERGY STAR makes the same point about energy. Bigger is better only up to the point you will actually run it.
The EPA says HEPA, as defined by the U.S. Department of Energy, means a filter that can theoretically remove at least 99.97% of particles 0.3 microns in size, the hardest size to catch; larger and smaller particles are trapped more efficiently (EPA, read 13 November 2026). CARB warns that ordinary high-efficiency filters are sometimes mistakenly called HEPA (CARB). Terms like "HEPA-type" or "HEPA-like" have no such definition, so treat them as unverified. In practice the CADR matters more than the label, because CADR already reflects how well the whole machine removes particles.
For odors, smoke smell and VOCs you need a gas filter, usually activated carbon. The EPA says these can work when there is a large amount of material in the filter, "the thicker the better", and that CADR does not measure them (EPA). A thin carbon-dusted sheet is not the same thing as a bed of granules.
The EPA says these may emit ozone in some cases, and that research has not shown plasma, photocatalytic oxidation or UV light removing gases effectively in home units (EPA). CARB says ionizers and electrostatic units usually produce very little ozone but some produce enough to cause unhealthy exposure, so use them cautiously and maintain them (CARB). Some mainstream units include one: Coway lists a "bipolar device" as one of the AP-1512HH's four stages (Coway). If a model has one, check the manual for whether it can be switched off and check the CARB certified list.
AHAM warns that unverified third-party filters may reduce airflow and particle removal, and now runs a program that verifies replacement filters perform equal to the original (AHAM Verifide). A cheaper filter that lowers CADR quietly undoes the sizing work above.
This is the one hard rule. The EPA says no federal agency has approved ozone generators for use in occupied spaces, that ozone is a lung irritant, and that at concentrations within public health standards ozone has little ability to remove indoor pollutants. It cites a study where a generator marketed for spaces up to 3,000 square feet, run on high in a 350 square foot room, produced 0.50 to 0.80 ppm, 5 to 10 times public health limits (EPA, read 13 November 2026). Ozone also does not remove dust or pollen.
California requires every portable indoor air cleaner sold in the state to be certified by CARB for ozone and electrical safety (CARB); certified units cannot emit more than 0.050 ppm of ozone (CARB fact sheet). Even if you live elsewhere, CARB's certified list is a free screen. Be wary of terms the EPA flags as misleading, such as "energized oxygen" or "pure air".
The sticker price is often the smallest part of what an air purifier costs. ENERGY STAR says a standard room air cleaner running continuously uses about 394 kWh a year, more than some new refrigerators, and that certified models are more than 50% more efficient, saving about 211 kWh a year (ENERGY STAR, read 13 November 2026).
| Item | 24 hours a day | 8 hours a day |
|---|---|---|
| Rated power (maker) | 77 W | 77 W |
| Hours per day (our assumption) | 24 | 8 |
| Energy per year | 77 x 24 x 365 / 1,000 = 674.5 kWh | 77 x 8 x 365 / 1,000 = 224.8 kWh |
| Electricity at 18.16 cents/kWh (EIA) | $122.49 | $40.83 |
| Filters per year (one $59.79 set) | $59.79 | $59.79 |
| Running cost per year | $182.28 | $100.62 |
| Five-year total incl. $143.99 sale price | $1,055.39 | $647.09 |
At 24/7 on high, five years of electricity and filters ($911.40) cost more than six times the sale price. Even on the gentler schedule, running costs are about three and a half times the purchase price. Using the same EIA rate, ENERGY STAR's 394 kWh benchmark costs about $71.55 a year and its 211 kWh saving is worth about $38.32 a year, in line with the $18 to $40 range ENERGY STAR quotes.
Yearly electricity = watts x hours per day x 365 / 1,000 x your price per kWh. Yearly filters = filter price x replacements per year. Add both, multiply by the years you expect to keep it, and add the purchase price. Filter prices vary even within one brand: Levoit lists its Core 300 Series Original Filter at $29.99 and a smoke-remover version at $39.99 (Levoit, checked 13 November 2026), so price the exact filter you would buy.
Also remember the EPA's ranking: removing the source of pollution and ventilating come first, and filtration supplements them. An air cleaner will not fix a mold or moisture problem.
At least two-thirds of the floor area in square feet, using the smoke CADR. A 10 by 12 foot room (120 square feet) needs a smoke CADR of about 80. Go higher for ceilings above 8 feet, and for wildfire smoke AHAM suggests a smoke CADR equal to the full square footage.
No. A higher CADR cleans the air faster, but CARB advises against an oversized unit because larger cleaners are usually louder and use more energy. Size for your room, with some headroom if you want to run it on a quieter low setting.
HEPA, as defined by the U.S. Department of Energy and described by the EPA, means at least 99.97% removal of 0.3 micron particles. HEPA-type or HEPA-like has no official definition, so check the certified CADR instead of relying on the label.
It depends on wattage, hours and your electricity rate. A 77 W unit running all day at the August 2026 U.S. average of 18.16 cents per kWh uses about 674.5 kWh and costs about $122 a year in electricity, before filters. At 8 hours a day it is about $41.
Avoid any device that intentionally produces ozone; the EPA says none is approved for occupied spaces. Ionizers and electrostatic units usually emit little ozone but some emit more, so CARB advises caution. CARB-certified units must emit no more than 0.050 ppm of ozone.
No. The EPA says the ENERGY STAR label refers to energy efficiency only, not air-cleaning effectiveness. Use the AHAM-verified CADR for performance and ENERGY STAR for running costs.