Portable air cleaners explained

A portable air cleaner, also called an air purifier, pulls air through a filter to clean the air in a single room or area. The furnace or HVAC filter does the same job for the whole house, but only while the system runs. Neither removes all the pollutants from the air. The most effective ways to improve indoor air are to remove the sources of pollution and to ventilate with clean outdoor air.

Particles and gases

Most filters are built to catch either particles or gases. A high-efficiency particulate air, or HEPA, filter catches particles such as dust, pollen and smoke. An activated carbon filter takes up gases, and it works best when it holds a lot of carbon. Many air cleaners carry one filter of each kind, and others have only a particle filter.

What the CADR means

Most portable air cleaners carry a clean air delivery rate, or CADR, usually measured at the highest fan speed. The higher the CADR, the more particles the unit removes and the larger the room it can serve. The CADR rates particles only. No widely used rating exists for gases.

Some labels give three CADRs, for tobacco smoke, dust and pollen. These stand for small, medium and large particles. The tobacco smoke number is the one for the smallest particles, which are of greatest health concern.

The figures assume an 8-foot ceiling. A room with a higher ceiling, or an open floor plan, needs a higher CADR.

Running one

• Where. In the room you spend the most time in, with nothing blocking the airflow, away from curtains. If it makes a draft, turn the airflow away from you.
• How fast and how long. Higher fan speeds and longer run times both filter more air.
• The filter. Every filter needs replacing. A dirty, overloaded filter doesn't work well.
• The ENERGY STAR label. On an air cleaner, it means the unit meets energy efficiency guidelines. It says nothing about how well it cleans the air.

What it can't fix

An air cleaner doesn't solve a mold problem. Mold grows from a water or moisture problem, so the fix is to stop the moisture and clean up the mold.

Ozone

Some devices sold as air cleaners, called ozone generators, make ozone on purpose. Ozone is a lung irritant, and no federal agency has approved these devices for use in occupied spaces. Some electronic air cleaners, such as ionizers, electrostatic precipitators and plasma units, may also give off ozone.

An annotated example

What to do next

Note your air cleaner's model and filter size in your home records, and check the filter and replace it when it looks dirty. Keeping wildfire smoke out of the house covers using one on a smoky day.