WILDFIRE SMOKE FACTSHEET 

Indoor Air Filtration 

When wildfre smoke gets inside your home it can make your indoor air unhealthy, but there are steps you can take to 

protect your health and improve the air quality in your home. Reducing indoor sources of pollution is a major step toward 

lowering the concentrations of particles indoors. For example, avoid burning candles, smoking tobacco products, using 

aerosol products, and avoid using a gas or wood-burning stove or freplace. Another step is air fltration. This fact sheet 

discusses efective options for fltering your home’s indoor air to reduce indoor air pollution. 

Filtration Options 

There are two efective options for improving air f ltration 

in the home: 1) upgrading the central air system f lter, 

and 2) using high efciency portable air cleaners. Before 

discussing fltration options, it is important to understand 

the basics of f lter ef ciency. 

Filter Ef ciency 

The most common industry standard for f lter ef ciency 

is the Minimum Ef ciency Reporting Value, or “MERV 

rating.” The MERV scale for residential flters ranges from 1 

through 20. The higher the MERV rating the more particles 

are captured as the air passes through the f lter. Higher 

MERV (higher ef ciency) flters are especially ef ective at 

capturing very small particles that can most afect health. 

Central Air System Filter 

The flter used in the central heating/cooling system 

of the home can efectively reduce indoor particle 

concentrations when the system is operating or when 

only the fan is turned on. Most home systems use a low 

MERV (1-4) f berglass flter that is 1” thick. Replacing 

this flter with a medium ef ciency flter (MERV 5-8) can 

signifcantly improve the air quality in your home. Higher 

ef ciency flters (MERV 9-12) will work even better, and a 

true high ef ciency 

flter (MERV 13-16) can reduce indoor particles by as much 

as 95 percent. Filters with a High Ef ciency Particulate 

Air (HEPA) rating, (or MERV 17-20) are the most efcient. 

You may need to consult with a local heating and air 

technician or the manufacturer of your central air system 

to confrm which (or if ) high ef ciency flters will work 

with your system. If you can’t switch to a more efcient 

flter, running the system continuously by switching the 

thermostat fan from “Auto” to “On” has been shown to 

reduce particle concentrations by as much as 24 percent. 

Portable Air Cleaners 

Portable air cleaners are self-contained air f ltration 

appliances that can be used alone or with enhanced 

central air fltration to efectively remove particles. How 

well they reduce air particle concentrations depends on 

several factors such as the size of the air cleaner, the area 

to be cleaned, the f lter efciency, how frequently the 

unit is turned on and the fan speed. Portable air cleaners 

ftted with high ef ciency flters can reduce indoor particle 

concentrations by as much as 85 percent. Furthermore, 

portables can be operated continuously at a lower cost 

compared to the continuous operation of a central system. 
 

 

Choosing a Portable Air Cleaner 

There are a wide variety of air cleaners on the market, 

ranging in price from about $50 to $3,000. Air cleaners 

that cost less than about $200 often do not clean the 

air as well and may not be helpful for wildf re smoke. 

Types of Air Cleaners 

Most air cleaners fall under two basic categories: 1) 

mechanical and 2) electronic. 

Mechanical air cleaners operate by pulling air through 

a flter that traps particles. Mechanical air cleaners 

are very reliable and do not produce ozone, an air 

pollutant that is a known health hazard. Filters in 

these devices need to be replaced according to the 

manufacturers’ recommendations, or when the f lter is 

dirty and the air cleaner is not operating ef ciently. 

Electronic air cleaners often use an electrical charge 

to charge particles and remove them from the air. 

The three main types of electronic air cleaners 

are electrostatic precipitators (ESPs), ionizers, and 

intentional ozone generators. ESPs have plates 

(collectors) that need to be cleaned when they get 

dirty. Ionizers work by making particles deposit on 

nearby materials. Ozone generators produce large 

amounts of ozone, and should never be used in 

homes or other occupied spaces. Other types of 

electronic air cleaners use ultraviolet (UV) bulbs and 

surface coatings like titanium dioxide to improve the 

removal of pollutants. However, these devices can 

emit ozone and some that are designed to remove 

chemicals actually emit volatile organic chemicals 

into the air. This includes devices that are sold as 

“hydroxyl” generators. 

Electronic air cleaners are not currently regulated, 

except in California. Caution should be used when 

selecting an electronic air cleaner, as they may 

generate ozone and/or other potentially harmful 

chemical compounds. Air cleaners certifed as being 

ozone-safe can be found on California’s list of certif ed 

air cleaners at: https://www.arb.ca.gov/research/ 

indoor/aircleaners/certif ed.htm. 

Size Rating of Air Cleaner 

When purchasing an air cleaner, check the square 

footage rating of the device to be sure that the 

air cleaner capacity is appropriate for the space it 

is intended to clean. A useful way to estimate the 

proper size device is the Clean Air Delivery Rate, or 

CADR, which is the removal efciency for a specif c 

size particle and volume of air delivered by an air 

cleaner in one minute. A useful tool to determine the 

appropriate air cleaner size for the intended space can 

be found at http://www.ahamdir.com. 

Ef ciency and Noise 

For best results, the portable air cleaner you purchase 

should have a flter rated as “high ef ciency” (high 

MERV) or HEPA. The flters for these devices may 

be more expensive but will do a much better job 

of cleaning the air than devices with cheap, low 

ef ciency f lters. 

Noise level is also an important consideration, as some 

air cleaners can be quite loud when operating at the 

maximum settings. If noise level is important to you, 

look for models with low noise ratings, or those that 

are rated by a reputable reviewer as quiet. 

U.S. Environmental Protection Agency · EPA- 452/F-18-005

• California Air Resources website: https://www.arb.ca.gov/research/indoor/aircleaners/

consumers.htm

• Learn about home air cleaners: https://www.epa.gov/indoor-air-quality-iaq/guide-air-cleaners-home 

For more information on air cleaning devices: