NorthWestern Energy residential customers can receive a $100 rebate toward Energy Star Certified HEPA air purifiers. Prepare your home today. The rebate form is HERE. Note: this is a new rebate form as of  July 1, 2022. For more about NWE rebates, head to their website HERE). Check out our recommended air purifiers below and see all Energy Star Certified HEPA portable air cleaners HERE!  
What is a HEPA Portable Air Cleaner (aka HEPA PAC or HEPA Filter)?
HEPA portable air cleaners (PACs for short), also known as air filtration units, 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 affecting Montana more frequently as our climate changes.

HEPA PACs typically come with replaceable carbon pre-filters that also remove the Volatile Organic Compounds in wildfire smoke (benzene, acrolein, formaldehyde, etc.). Pre-filters take care of larger particles such as pollen, too.  

HEPA filters are available for central heating and cooling systems as well, but here we talk exclusively about portable units that use replaceable HEPA filters and plug into a standard wall outlet. Click HERE for more information about filters used in central heating and cooling systems.
Here's a short video with most of what you need to know when it comes to HEPA PACs.  Thanks Sarah Coefield!
How Do I Know Which Model to Buy?

Most importantly, make sure the unit uses a genuine HEPA 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 PAC you choose is labeled HEPA, not HEPA-like. True HEPA PACs 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.
  • ​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 Portable Air Cleaners 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.  Links go to the manufacturer - you can often find these for less money at local box or hardware stores or online. 

  • 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 refurbished Winix c535 are a great deal right now!
  • 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.

​​For more options, check this list of approved filters from the California Air Resources Board (CARB) here.
How Should I Use my HEPA PAC?

We highly recommend using your HEPA PAC 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 PACs, simply keep it in the room you spend the most time, with the doors open between rooms.

HEPA PACs 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 VOCs is worth it.