Wisconsin Air Duct Pros guide

Wildfire Smoke Days and Your Furnace Filter: What Wisconsin Homeowners Can Do

When wildfire smoke drifts into Wisconsin, a practical step for homes with a forced-air system is to filter the air the system already moves: keep windows and doors closed, use the highest-efficiency filter your system can handle (EPA suggests MERV 13 if possible), and run the fan. Duct cleaning isn't a smoke remedy; consider it only if you see the specific signs EPA describes.

Updated October 19, 2026Sources listed below

Why smoke is a Wisconsin question

In its 2024 air quality trends report, the Wisconsin DNR said wildfire smoke events in 2023 resulted in 15 PM2.5 air quality advisories, almost five times higher than the average over the previous 12 years. During a multi-day advisory in late June, the state's monitoring network measured some of the highest PM2.5 concentrations ever recorded in Wisconsin.

Most Wisconsin homes already have equipment that can help. In EIA's 2020 Residential Energy Consumption Survey, about 78% of Wisconsin homes used a furnace as their main heating equipment, and EPA notes that running a system's fan with a good filter helps remove particles while air quality is poor.

Sources: Wisconsin DNR: DNR Releases 2024 Air Quality Trends Report; U.S. EIA: 2020 RECS, Highlights for space heating in U.S. homes by state; U.S. EPA: Wildfires and Indoor Air Quality

What to do with a forced-air system on a smoke day

EPA and the Wisconsin DNR offer overlapping advice for homes with central systems:

Close windows and doors.
Set the system to recirculate, or close the outdoor air intake damper if your system has one.
Run the system fan as often as possible by switching it from "Auto" to "On".
Use a new high-efficiency filter, and keep spares on hand in case smoke loads it quickly.
Avoid adding indoor particles during the event: skip burning candles and frying food, and don't vacuum unless your vacuum has a HEPA filter.

Sources: U.S. EPA: Wildfires and Indoor Air Quality; Wisconsin DNR: Wildfire Smoke

Choosing a higher-rated filter safely

EPA suggests a MERV 13 filter, or as high a rating as your system's fan and filter slot can accommodate, and says you may need to consult an HVAC technician to find the highest-efficiency filter your system can take.

Fit matters as much as rating. EPA says the filter should fit snugly so air doesn't leak around it, and it should not be bent or crushed to fit. During heavy smoke, change it when it appears dirty, which may be sooner than the manufacturer's usual schedule.

Source: U.S. EPA: Wildfires and Indoor Air Quality

Is duct cleaning useful after smoke?

Usually not as a first response. EPA's wildfire guidance says you may consider duct cleaning after a fire, but that ducts should only be cleaned as needed, for example when they're clogged with excessive dust and debris or particles are actually released into the home from the supply registers.

EPA's duct guidance adds that much of the dirt in air ducts adheres to duct surfaces and does not necessarily enter the living space, and that dirty ducts are only one of many possible sources of particles in a home. If you see those signs, a cleaning visit can make sense, but we won't claim it makes the air healthier. EPA says duct cleaning has never been shown to actually prevent health problems.

Sources: U.S. EPA: Wildfires and Indoor Air Quality; U.S. EPA: Should You Have the Air Ducts in Your Home Cleaned?