Air purifier FAQ

Clean Air Delivery Rate is the volume of genuinely clean air a purifier delivers per minute, measured under ANSI/AHAM Standard AC-1. It combines filter efficiency and airflow in one number, which means a machine cannot game it with a superb filter and a weak fan, or the reverse. Filter grade describes one half of that equation. The full explainer.

AHAM’s rule is that CADR should be at least two-thirds of the room’s floor area, assuming an 8-foot ceiling. A 300 square-foot room needs about 200 CFM; a 150 square-foot bedroom about 100. The calculator does it for your room.

Because they measure different things. Manufacturers usually advertise coverage at one air change per hour; AHAM’s certified suggested room size is based on 4.8 air changes per hour. Both come from the same test data, and the gap is routinely between four and five times. One popular unit advertises 2,800 square feet and is certified for 574.

A certified figure has been verified by an independent laboratory and listed in a public register you can search. A claimed figure is published by the company selling the machine with no independent listing. The claimed figure may well be accurate — the difference is that one is checkable by you.

The EPA reports that multiple studies with portable HEPA air cleaners have found improvements in one or more allergy and asthma symptoms, and adds that the studies do not always show major improvements and do not show improvements in all symptoms. That is a real but modest and variable effect, reported as written.

Source control and ventilation. The EPA states that the most effective ways to improve indoor air are to reduce or remove the sources of pollutants and to ventilate with clean outdoor air, and that filtration does not replace the need to do those. In a pet household that means keeping the animal out of the bedroom and washing bedding hot.

The EPA advises avoiding portable air cleaners that intentionally produce ozone, noting ozone is a lung irritant, and names ionizers and plasma cleaners among technologies that may emit it. Measured emissions on certified units are small — the ones we cover range from 0.00 to 5 ppb against a 50 ppb program limit. If someone in the house has asthma, choose a machine measuring 0.00. The detail.

No. The EPA states that no federal government agency has approved these devices for use in occupied spaces, and advises avoiding air cleaners that intentionally produce ozone. Why they are a different product entirely.

No. It is a marketing phrase with no certifying body behind it in the consumer purifier market. The certification registers do classify filters as HEPA or HEPA-Type, and several units sold as True HEPA are recorded as HEPA-Type. What that means.

Among the certified units we cover, annual energy use runs from 95 to 657 kWh — roughly $17 to $121 a year at 18.34 cents per kWh. Filters typically add $30 to $120 more. The spread is not correlated with purchase price. Computed for every unit.

Follow the manufacturer’s interval as a starting point and check the filter visibly, because published intervals assume general household use and a shedding pet shortens them materially. Carbon stages need replacing more often than HEPA stages, because carbon saturates rather than clogs.

In a pet or allergy household, yes. The source is continuous, so a machine running in bursts is always catching up. This is why running cost and noise matter so much: the machine you can afford and tolerate leaving on is worth more than a stronger one you switch off.

Near the source of the problem, with at least a foot of clear space around the intake and outlet, in a room with the door closed. A machine pushed against a wall or behind furniture recirculates its own clean output. Placement in full.

They capture the airborne fraction, which reduces how much settles elsewhere. They do nothing about hair already on the floor or furniture — that is a vacuum’s job. In a shedding household the feature that matters most is a washable pre-filter.

Almost certainly because it contains very little activated carbon. Odor removal is adsorption onto carbon and scales with carbon mass; a budget unit may hold tens of grams where a machine built for odor holds hundreds. HEPA media does nothing for smell — odor molecules are gases.

It captures airborne spores while running. It does not remove mold from surfaces or stop it producing spores, because mold grows where something is wet. Fix the moisture first; a dehumidifier is the appliance doing the structural work there.

Broadly yes, because closed doors block air exchange and a purifier only cleans the space it is in. A machine sized for a bedroom is not sized for a bedroom plus the hallway. Two correctly sized machines usually beat one large one placed centrally.

Up to a point. Once certified CADR comfortably clears AHAM’s rule for your room, extra capacity mainly buys the ability to run at a lower, quieter fan speed — which in a bedroom is exactly what decides whether the machine stays switched on.

No. We have no lab, we do not own these machines, and we say so on every relevant page. What we do instead is compile third-party certified figures from AHAM and ENERGY STAR, apply the published sizing standard, compute running costs at a stated electricity rate, and cite primary sources. Our method in full, including where it runs out.

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