Although we can't get rid of the smoke outdoors, there are a number of options for limiting exposure to harmful, smoky air. 

Hepa Filter for wildfire smoke

What is a HEPA Filtration Unit?
HEPA air filtration units, also known as air purifiers, are portable appliances that filter out really tiny particulate matter (PM) - 2.5 microns and smaller. These ultrafine bits are the most common and dangerous component of wildfire smoke, which is rolling into the Missoula Valley more frequently as our climate changes.

HEPA air filtration units typically come with replaceable carbon pre-filters that also remove the Volatile Organic Compounds in wildfire smoke (benzene, acrolein, and formeldehyde for example). Pre-filters take care of larger particles such as pollen, too.  And one more bonus: because the units blow out filtered air, they double as fans!

HEPA air filters are available for central heating and cooling systems as well, but here we'll be talking exclusively about portable filtration units that use small HEPA filters and plug into a standard wall outlet in your home. Click here for more information about filters used in central heating and cooling systems.
How Do I Know Which Model to Buy?

Most importantly, make sure the unit uses a genuine HEPA air filter. Other filter types and air purification methods may not filter the smallest PM that causes the greatest health problems, and some release small amounts of ozone gas - which isn't good for people or the planet!  If your unit has a "PlasmaWave" function, we recommend turning this off (it may emit a very small amount of ozone). Avoid "HEPA-like" units. 

Key considerations:
  • True HEPA. Make sure the air filtration unit you choose is labeled HEPA, not HEPA-like. True HEPA filters are able to filter out 99.7% of particles down to 0.3 um. Some units only filter down to 3 microns - which means they do NOT filter out smoke.
  • Room size. Buy the right air filtration unit to fit the room where you'll use it most frequently. (We recommend the bedroom; see below.) Most units list the size room they can filter effectively. Others list a Clean Air Delivery Rate (CADR), in which case, choose a tobacco smoke CADR at least 2/3 the room’s area. For example, a 10’ x 12’ room (120 square feet) would require an air cleaner with a tobacco smoke CADR of at least 80.
  • Filter maintenance.​ Most HEPA filters must be replaced from time to time. A few models can be cleaned with occasional washing or vacuuming. Consider how much cleaning you're capable of doing, and how much you're willing to spend on replacement filters. 
  • Noise level. Some units are noisier than others. If this is a concern, check user comments and feedback online.
  • Energy Star rating. To save energy and money on your electricity bill, choose units with the U.S. Department of Energy's Energy Star rating.
  • Cost. Consider the factors above and purchase what you can afford. Look for sales of course!
HEPA Filters We Recommend

All of our recommended air filtration units filter PM as small as 0.3 microns and have an Energy Star rating. All are available online, and some are available in local stores. Prices vary depending where you buy them. These are by no means the only good filters, just a helpful start.  
  • The Winix 5300-2 works for rooms up to 360 square feet and costs about $150-200. It comes with four replaceable carbon pre-filters.
  • The Winix 5500-2 ​is very similar to the 5300-2 model. It also has a remote control, and costs ~$230. Both the Winix 5300 and 5500 filters are particularly quiet and have good CADR specifications.
  • The Lasko Pure Silver HF25610 works for rooms up to 160 square feet and costs about $160. It has replaceable filters and may be available at ACE Hardware. 
  • The Honeywell HPA 160 works for rooms up to 170 square feet and costs about $180. It has replaceable filters.
  • The Germ Guardian AC4825 works for rooms up to 150 square feet and costs about $100. Replace the filter when it turns gray.

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​Again, Check this list of approved filters from the California Air Resources Board (CARB) here.
How Should I Use my HEPA Air Purifier?

We highly recommend using your HEPA air filtration unit in your bedroom at night. This way your body gets a break while you sleep, and for most people, this is the longest period of time you'll spend in one room. For most of us, the portable nature of these units allow you to move them to a more central room during the day.  For people who cannot move their filter, simply keep it in the room you spend the most time, with the doors open between rooms.

HEPA air filters work best when all windows and outside doors are closed. This is easy in the winter, but it can be more complicated with hotter weather during wildfire season. During hotter days, we generally recommend closing windows and blinds to keep your home cool, then opening them back up at night to draw in cool air. When it's both smokey and hot, this is difficult and the best thing to do is carefully assess the current air quality and balance that with the health risks from overheating. This is especially a concern for the elderly. 

Often the air is cleaner and starting to cool in the evening, providing an opportunity to open windows, run fans if you have them and then close them again just before going to bed in anticipation of nighttime smoke settling patterns.  Again, if your home is sweltering, it could be more important to cool off your bedroom than to clean the air. Fans help a bunch, as can air conditioners set on recirculate (remember to clean or replace your A/C filter). For more tips on how to cool your home, see Climate Missoula's Hotter Days, Warmer Nights and Fans, A/C, and Coolers pages.

Change your filters! Especially if you are using an activated carbon pre-filter to remove volatile organic compounds (VOCs), be sure to change the filters frequently, as they can be quickly saturated with particles. Activated carbon pre-filters can be pricey, but for some folks the removal of VOC' is worth it.

Home and office Fixes

Minimize potential health impacts of smoke by reducing other pollutants in your home, changing the settings on your central cooling systems, and more.
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  • Avoid smoking cigarettes, burning candles or incense, using wood stoves, and vacuuming during smoky periods (each of these causes unhealthy particulates to circulate in your indoor air).
  • Run any heating or cooling system in your home or workplace on recirculate to help filter particles out of your indoor air and minimize smoke entering from outside air.
  • Have a several day supply of food that does not require cooking. Cooking - especially frying and broiling - can add to indoor pollution levels.
  • Build or grow shade around your home to keep cool so that keeping windows shut is easier during smoke. Visit Climate Smart's Grow It-Build It page for tips on how to cool your home. The Smarter House website also has good information on efficiently cooling homes.
Easy Tips for Improving Air Quality - Heating and Cooling Systems
​All centralized heating and cooling systems have a filter component. The filter can often be found where the main system is located, where outdoor air is being pulled inside. For example, in a typical home furnace system, the filter is often placed before the blower motor, in a space between an air duct and the heating aspect of the furnace. Filters are designed to reduce pollution of our indoor air, and are rated on an effectiveness scale by ASHRAE, the American Society of Heating, Refrigerating, and Air-Conditioning Engineers. These MERV (minimum efficiency reporting value) ratings vary from 1 to 20 depending on how well they filter different sizes of pollutants. Below is a chart that displays the effectiveness of different MERV rated filters.
For wildfire smoke, filters rated at least 13 are effective in reducing harmful particles in the air. Filters rated below 13 cannot effectively trap the harmful particulates in wildfire smoke. However, these higher rated filters can strain old heating and/or cooling systems, so consider asking an HVAC technician to check your system before upgrading your filter. Also,  using a finer filter will cause your system to use more energy to push air through, so think about putting a lower rated filter back in after the smoke clears away.

Most heating and cooling systems are able to shut off the inflow of outdoor air and simply recirculate indoor air. This is helpful during wildfire smoke because it allows your indoor air to be filtered multiple times, and prevents smoke from coming inside. Find out if your system can be switched to recirculate indoor air. Remember to re-adjust your settings when the smoke clears so that your home or office can have fresh air.

Smoke Leakage
Smoke particles are tiny, and can seep through small cracks in your building. In order to let your filters do their job, make sure to keep doors and windows closed as much as possible and block off any other routes for outdoor air to get inside.

Public clean air spaces

If you can't escape the smoke in your own home or office, spend some time in a public indoor space that has filtered air. Even a small amount of time in clean air each day during a smoke event will help to keep you healthy.  Use the smoke as a time to catch up on reading in your local library, see a movie, go to a museum, or indoor concert. 

Not all indoor spaces have clean air. Sometimes, indoor air can be just as bad as outside. By asking the right questions, you can find out which indoor spaces have clean air. See the 6 Steps to Ensure Indoor Air Infographic (below).
 What to ask:
  • Do you keep windows and doors shut?
  • What is the MERV rating of the filters in your central air system?
  • Do you run your system on recirculate when the smoke is bad, to stop bringing outside air inside?
Good Answer
  • Yes, as much as possible (If a businesses needs to open windows to cool their building at night - we recommend windows are shut in the morning and a filtration system is running for at least an hour before people arrive)
  • MERV 13 or higher (There is some benefit with filters rated as low as a MERV 8 as long as the air system is run on recirculate and the filters are replaced FREQUENTLY) 
  • Yes, recirculate is on when air quality outside is designated "unhealthy"
*Whenever systems are switched to recirculate, carbon dioxide levels should be monitored.
If the location does not have air conditioning, it is important to find out whether the heating system can blow unheated air on recirculate - if this is done for an hour or more every morning after shutting all windows and doors, the (MERV13+) filter may be able to catch many of the unhealthy particles. 

Remember that filters and pre-filters must be replaced more often during smoke events.

Encourage your office building or favorite public indoor spaces to be prepared for wildfire smoke and to provide clean air!
To learn more about MERV ratings and central air systems during wildfire smoke click here.