What an Air Cleaner Can — and Cannot — Do

An air cleaner can help people with allergies, smoke, and dust.

But it cannot solve every indoor air problem.

According to the Environmental Protection Agency, an air cleaner will not lower radon levels in a home. It also will not fix the source of a mold problem, and many units do little to remove gases released by fresh paint, new carpet, or other household products.

No air cleaner removes everything.

A good portable unit can reduce airborne particles, including pollen, dust, pet dander, mold spores, and wildfire smoke.

One important number to check is the CADR, or clean air delivery rate.

The rating, used by the Association of Home Appliance Manufacturers, tells consumers how much filtered air a machine can deliver. Separate ratings may be given for smoke, dust, and pollen.

AHAM recommends choosing a unit with a CADR of at least two-thirds of the room’s square footage.

For example, a 300-square-foot bedroom would require a CADR of at least 200.

A HEPA filter is also worth looking for.

True HEPA filters are designed to capture at least 99.97% of airborne particles at 0.3 microns under test conditions.

Terms such as “HEPA-type” or “HEPA-like” do not necessarily meet the same standard.

If odors or certain gases are a concern, look for a unit that also includes activated carbon.

Carbon can help trap some gases and odors, but its effectiveness depends heavily on how much carbon the machine contains and how quickly the filter becomes saturated.

One type of machine to avoid is an ozone generator.

The EPA warns that ozone can irritate the lungs and, at levels considered safe for people, is generally not effective at removing many common indoor pollutants.

Consumers can also look for certification from the California Air Resources Board, or CARB, which limits ozone emissions from indoor air-cleaning devices sold in California.

Cigarette smoke is especially difficult.

A HEPA filter can capture many of the particles in smoke, while activated carbon may help reduce some of the gases and odors.

But an air cleaner cannot remove smoke residue that has settled into walls, carpets, curtains, and furniture.

Finally, check the ongoing cost.

Replacement filters can add significantly to the price of owning a purifier, and noise matters too.

The best air cleaner is not just one that tests well.

It is properly sized for the room, uses the right filters for the problem, and is quiet enough that you will actually keep it running.