The Role of HVAC in Protecting Against Wildfire Smoke

May has arrived in Arizona with its warm days and cool nights, perfect for spending time outdoors. However, May is also the start of Arizona’s wildfire season. Warmer temperatures and a drier monsoon season have increased the number of fires and the length of the season. The Department of Forestry and Fire Management recorded over 1,500 wildfires in Arizona in 2024.

More fires and an extended season mean more smoke. Where wildfire smoke was once a minor inconvenience, it is now often a health risk. The fine particulate matter (2.5 μm or less in aerodynamic diameter) penetrates and deposits deep in the lungs. Your HVAC system can help filter harmful particles during Arizona’s wildfire season.  

Why Is Wildfire Smoke Dangerous?

Wildfire smoke contains fine particles (PM2.5) and many other pollutants. Particles less than 2.5 micrometres in diameter may irritate the eyes, throat, nose, and lungs, causing wheezing, coughing, sneezing, and shortness of breath. Short-term exposure aggravates conditions such as heart disease, bronchitis, and asthma. Prolonged exposure to PM2.5 is associated with an increased rate of bronchitis, lung cancer, heart attack, stroke, and reduced lung function. Children, pregnant women, and seniors are at particular risk. 

How An HVAC System Can Help Protect Against Wildfire Smoke?

When wildfire smoke is present, your HVAC system can help by:

• Recirculating air: When wildfire smoke is present, switch your HVAC to recirculation/fan-on mode. This recycles the air in your home rather than drawing smoke-filled air from outside. When the smoke abates, reversing this setting draws fresh air indoors. Close fresh air intakes from fireplaces, stoves, and your HVAC system to prevent smoke-filled air from entering.  
• Filtering air: Equip your HVAC system with a high-quality filter (a MERV value of 13 or more) to remove fine particulate matter. Consider installing a prefilter (Merv value of 8 or more) to remove large particles before reaching your primary filter. Change your prefilter 2 or more times per year and your high-efficiency filter once per year. Put your HVAC system on fan-on/recirculation mode when wildfire smoke is present.

What Else Can You Do?

To prevent outside air from entering your home and to preserve the quality of indoor air:

• Seal doors and windows and keep them closed
• Limit the use of exhaust fans (bathroom and kitchen)
• Maintain a humidity level between 35% and 50%
• Refrain from burning candles/incense or using aerosol sprays
• Reduce the frequency of vacuuming (may release particles into the air)
• Refrain from vaping/smoking indoors
• Avoid broiling or frying foods

McMillin Air Can Help

Be prepared for wildfire season by servicing and repairing your current air conditioning unit or installing a new HVAC system. McMillin Air can help you with both. Ask us about high-quality filters for your system, and make sure your family is safe and comfortable this summer.