WILDFIRE SMOKE FACTSHEET
Indoor Air Filtration
When wildfire 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 fireplace. Another step is air filtration. This fact sheet
discusses effective options for filtering your home's indoor air to reduce indoor air pollution.
Filtration Options
There are two effective options for improving air filtration
in the home: 1) upgrading the central air system filter,
and 2) using high efficiency portable air cleaners. Before
discussing filtration options, it is important to understand
the basics of filter efficiency.
Filter Efficiency
The most common industry standard for filter efficiency
is the Minimum Efficiency Reporting Value, or"MERV
rating." The MERV scale for residential filters ranges from 1
through 20.The higher the MERV rating the more particles
are captured as the air passes through the filter. Higher
MERV (higher efficiency) filters are especially effective at
capturing very small particles that can most affect health.
Central Air System Filter
The filter used in the central heating/cooling system
of the home can effectively 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) fiberglass filter that is V'thick. Replacing
this filter with a medium efficiency filter (MERV 5-8) can
significantly improve the air quality in your home. Higher
efficiency filters (MERV 9-12) will work even better, and a
true high efficiency
filter (MERV 13-16) can reduce indoor particles by as much
as 95 percent. Filters with a High Efficiency Particulate
Air (HEPA) rating, (or MERV 17-20) are the most efficient.
You may need to consult with a local heating and air
technician or the manufacturer of your central air system
to confirm which (or if) high efficiency filters will work
with your system. If you can't switch to a more efficient
filter, 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 filtration
appliances that can be used alone or with enhanced
central air filtration to effectively 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 filter efficiency, how frequently the
unit is turned on and the fan speed. Portable air cleaners
fitted with high efficiency filters 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.

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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 wildfire 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 filter 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 filter is
dirty and the air cleaner is not operating efficiently.
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 certified as being
ozone-safe can be found on California's list of certified
air cleaners at: https://www.arb.ca.gov/research/
indoor/aircleaners/certified.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 efficiency for a specific
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.
Efficiency and Noise
For best results, the portable air cleaner you purchase
should have a filter rated as "high efficiency" (high
MERV) or HEPA. The filters for these devices may
be more expensive but will do a much better job
of cleaning the air than devices with cheap, low
efficiency filters.
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.
For more information on air cleaning devices:
California Air Resources website: https://www.arb.ca.qov/research/indoor/aircleaners/
consumers.htm
Learn about home air cleaners: https://www.epa.qov/indoor-air-quality-iaq/quide-air-cleaners-home
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AIR RESOURCES BOARD			"	^
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U.S. Environmental Protection Agency  EPA- 452/F-18-005

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