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EPA's order of operations is source control, then ventilation with outdoor air, then filtration. A portable cleaner is a supplement for particles in a room you actually occupy. It is not a mold contractor, a radon system, or a gas-phase miracle.
The argumentThe U.S. Environmental Protection Agency's indoor-air guidance puts source control first, ventilation second, and air cleaning third. Filtration can reduce particles in a room, including PM2.5, when the cleaner is sized for that room and actually runs. It cannot remove all pollutants, does not solve mold or moisture, is not recommended by EPA as a radon fix, and is generally not designed to remove gaseous pollutants unless it has a substantial sorbent filter. Buying a unit before naming the pollutant is how people end up with a humming box next to a gas burner they never vented.
Do I actually need a box with a HEPA filter, or should I open a window, fix the stove, and stop smoking indoors first?
EPA: the most effective move is usually to eliminate or reduce the source. Ventilation dilutes what remains. Filtration is a supplement, not a replacement.
Portable cleaners are room devices. CADR is a particle rating. Gases need a different filter, with no widely used consumer rating comparable to CADR.
Do not use a cleaner as the plan for mold, moisture, or radon. EPA says air cleaners are not a radon solution and do not address the cause of mold.
Avoid devices that intentionally produce ozone. ENERGY STAR on a cleaner is an electricity rating, not an air-cleaning endorsement.
The market for indoor air is a tower of boxes that promise hospital air in a studio apartment. The Environmental Protection Agency's actual sequence is less photogenic. First, stop making the pollution, or make less of it. Second, dilute what you cannot stop, with outdoor air that is itself reasonably clean. Third, if particles are still a problem in a room you live in, a filter that moves enough air can help. That third step is optional in the sense that it does not replace the first two. It is also the only step you can impulse-buy.
This page is the decision to use filtration at all. Matching a specific unit's Clean Air Delivery Rate to a room is the Reviews companion, How to choose a room air cleaner. If you skip this page, you can buy a correctly sized cleaner for the wrong problem.
Eliminate or reduce emissions. Smoke outdoors. Fix the gas range so it burns cleanly and exhaust it. Dry the wet drywall. Choose materials that off-gas less. EPA: usually the most effective, and often cheaper than running more ventilation.
Bring in outdoor air and exhaust the dirty air. Open windows when outdoor air is acceptable. Run kitchen and bath fans that actually duct outside. Most U.S. forced-air systems do not mechanically supply outdoor air. If outdoor air is smoke or a busy road, ventilation can import the problem.
A portable unit filters a room. A better furnace filter (EPA suggests at least MERV 13 if the system can take it) filters whatever air the HVAC actually moves. Effectiveness is collection efficiency times airflow. A tight filter that barely moves air, or a roaring fan with a weak collector, both fail.
What are you actually trying to reduce?
A portable cleaner with a CADR matched to the room, run at a speed you will tolerate, in the room you occupy. Or a higher-MERV HVAC filter if the system runs often enough. Still: stop the source if you can.
EPA: most air cleaners are not designed to remove gaseous pollutants. CADR does not measure gases. A thick activated-carbon bed can help some gases. Plasma, photocatalytic, and UV claims for residential gas removal are not something EPA's consumer guide treats as demonstrated.
EPA: portable cleaners and HVAC filters do not address the cause. Remove moisture, clean mold, fix the leak. A filter may catch some spores and take the edge off odor. It will not dry the house.
EPA does not recommend air cleaners to reduce radon and its decay products. They only partly remove decay products and do not stop radon entering. Test and mitigate the soil-gas path.
EPA's consumer guide is blunt about what filtration can do for health: possibly small improvements in some cardiovascular, respiratory, allergy, or asthma measures in studies that used portable HEPA cleaners. The improvements are typically small and not always noticeable to the person in the room. That is not a reason to skip a well-sized cleaner if particles are the issue. It is a reason not to sell yourself a medical device.
Houseplants are not a strategy. EPA's improving-IAQ page says there is currently no evidence that a reasonable number of houseplants remove significant quantities of pollutants in homes and offices, and overwatering can grow microorganisms. The NASA chamber studies were not your living room.
Ozone is a lung irritant. EPA tells people to avoid portable cleaners and HVAC gadgets that intentionally produce ozone. Some electrostatic precipitators, ionizers, poorly coated UV lamps, and plasma units can emit ozone even when ozone is not the marketing headline. California's Air Resources Board and AHAM keep lists of units tested for low ozone. ENERGY STAR on the box means the motor is efficient. EPA's own disclaimer on those products says the label is not an endorsement of healthier air.
If you have decided particles in a specific room are the remaining problem, leave this page and use CADR. EPA publishes an estimation table: about 65 cfm of CADR for 100 square feet with an 8-foot ceiling, scaling linearly, with a note to go higher for taller ceilings. The Reviews article walks the two-thirds rule and smoke-CADR detail. This page's job is to keep you from using that table on a radon problem.
Source, then outdoor air, then a sized particle filter in the room you use.
CADR is particles. Gases, mold moisture, and radon are other tools.
No ozone generators. ENERGY STAR is watts, not CADR.
EPA: filtration does not replace source control and ventilation. In wildfire smoke, you may close windows and filter. That is a bad-air-outside exception, not a lifestyle.
Only while the system runs, which EPA notes is often under 25 percent of the time in heating and cooling seasons. A MERV 13 filter helps the air that actually passes through. A portable unit in the bedroom still has a job at night if the furnace is off.
EPA: the room you spend the most time in, airflow unobstructed, not behind a curtain. If the jet of air is annoying, redirect it rather than turning the unit off.
Sources and further reading
EPA's three strategies: source control, improved ventilation, air cleaners/filtration. Source control is usually most effective. Air cleaners are generally not designed to remove gaseous pollutants. EPA does not recommend air cleaners to reduce radon. Houseplants: no evidence a reasonable number remove significant pollutants in homes.
Filtration supplements source control and ventilation. CADR sizing table for particles. CADR is particles only. Activated carbon for gases, no widely used gas rating. Mold: cleaners do not fix moisture. Avoid ozone-producing cleaners. ENERGY STAR is efficiency, not cleaning performance. EPA neither certifies nor recommends brands.
Continue reading
Most air cleaner marketing leads with filter type and app features. The number that actually predicts whether a unit will do anything in your room is its Clean Air Delivery Rate, and there is a simple rule for matching it to your space.
Reviews / Comparisons / 7 min
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