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Seasonal Guide

Wildfire Smoke Air Quality Guide, What AQI Numbers Mean for Your Home

Smoke can reach you even when the fire is far away. Here is what the AQI numbers mean, and what EPA says to do before, during and after a smoke event.

Last updated October 2026

Why Wildfire Smoke Is Different from Normal Dust

EPA says smoke is a mix of gases and fine particles made when wood and other things burn. The biggest health threat is the fine particles.

Fine particles (PM2.5) are generally 2.5 micrometers and smaller. A human hair is about 30 times wider than the largest of them. EPA says particles this small can get deep into the lungs, and some may get into the blood. They can cause burning eyes and a runny nose. They can make heart and lung disease worse.

Key Point

EPA says the biggest health threat from smoke is from fine particles. That is why PM2.5 is the number to watch in fire season, indoors and out.

The AQI Scale: All 6 Levels Explained

EPA's Air Quality Index has six color-coded levels. The higher the number, the more pollution and the bigger the health concern. The advice below is EPA's for fine particles, the main pollutant in smoke.

AQI RangeLevelWhat it means and what EPA says to do
0 to 50GoodAir quality is satisfactory. EPA: it's a great day to be active outside.
51 to 100ModerateAcceptable, but there may be a risk for unusually sensitive people. EPA: they should consider shorter, less intense outdoor activity.
101 to 150Unhealthy for Sensitive GroupsSensitive groups may have health effects. EPA: they should make outdoor activities shorter and less intense, and take more breaks.
151 to 200UnhealthySome of the general public may have effects. EPA: sensitive groups should consider moving activities inside; everyone else should keep outdoor activities shorter and less intense.
201 to 300Very UnhealthyHealth alert for everyone. EPA: sensitive groups should avoid all outdoor physical activity; everyone else should limit it.
301 and higherHazardousHealth warning of emergency conditions. EPA: everyone should avoid all physical activity outdoors.

Track current AQI at airnow.gov or on AirNow's Fire and Smoke Map. For real-time indoor readings, see our guide to the best air quality monitors.

Want to look up your own area? See how to check AQI by zip code. To learn where the number comes from, read how AQI is calculated.

How Smoke Gets Into Your Home

EPA says outdoor air, smoke included, gets in three ways:

  • Through open windows and doors.
  • Through fans and systems that pull outdoor air, like kitchen and bath fans that vent outside, or an HVAC system with a fresh air intake.
  • Through small cracks and gaps, even around closed windows and doors.

Rule of Thumb

Keep windows and doors closed while it is smoky. When the outdoor air gets better, even for a short time, EPA says to air out your home. Check AirNow first.

Pre-Event Prep, What to Do Before Fire Season

EPA says getting ready before fire season matters most for children, older adults, and people with heart or lung disease. Do this before smoke arrives:

  1. Seal gaps. Smoke gets in through cracks and gaps around doors and windows. Weatherstrip doors and add door sweeps where you can see light.
  2. Upgrade your HVAC filter. EPA suggests MERV 13 or as high as your system fan and filter slot can take. Make sure it fits snugly. An HVAC pro can tell you what your system can handle.
  3. Get your air purifier ready. Pick one sized for the room, and make sure it does not make ozone. Keep a spare filter, since EPA says to change filters more often during heavy smoke.
  4. Stock N95 respirators.EPA says to keep a supply on hand. Look for “NIOSH” and “N95” printed on the mask.
  5. Learn your HVAC settings. Find out if it has a fresh air intake, and how to close it or switch to recirculate.
  6. Set up an air quality monitor. One with a PM2.5 sensor shows your indoor particle level instead of guessing from outdoor AQI.

During a Smoke Event, Room by Room

If local officials tell you to stay indoors, EPA says to keep windows and doors closed and cut the smoke coming in.

Clean room (top priority)

EPA says to put a portable air cleaner where people spend the most time and run it as often as possible on the highest fan speed. AirNow says air cleaners work best run nonstop with doors and windows closed. A bedroom is a good choice.

Whole house

If your HVAC has a good filter, set it to recirculate and the fan to “On” instead of “Auto”. Check the filter often and change it when it looks dirty.

Kitchen

EPA says to avoid frying or broiling, gas and wood stoves, and candles while it is smoky. Kitchen fans that vent outside are one way outdoor air gets in.

Bathroom

Bath fans that vent outside can also bring outdoor air in. Save them for when the air gets better, which is when EPA says to run them.

EPA also says to skip vacuuming unless your vacuum has a HEPA filter, and to keep cool. If you cannot stay cool at home, go somewhere that is.

If you must go outside, wear a well-fitted N95. AirNow says cloth masks will not protect you from smoke.

When to Leave vs Shelter

EPA says that if a fire is very close, it may be best to leave, because it can be nearly impossible to keep dense smoke out. Follow local emergency alerts and leave right away if you are told to. No purifier replaces leaving when the fire is close.

Post-Event Cleanup, Getting Your Home Back to Normal

After the smoke clears, ash can settle inside and get stirred back into the air. EPA and AirNow say:

  1. Air out the house when the air is better. Open windows and run the kitchen and bath fans. Check AirNow first.
  2. Keep kids out of cleanup. EPA says children, older adults, and people with heart or lung disease should not do cleanup work.
  3. Wear an N95 for ash. Wear gloves, long sleeves and long pants too.
  4. Do not dry sweep. Mist surfaces with water first, then wet mop. Use a damp cloth on light dust.
  5. Use a HEPA-type vacuum. If you vacuum, use one with a HEPA filter.
  6. Clean fabrics. AirNow says to clean carpet, upholstery, window treatments, bedding and clothing.
  7. Check your filters. Change HVAC and purifier filters when they look dirty.

Monitoring Tools Worth Having

We may earn a commission at no extra cost to you.

These three products help you see particles in your air and filter smoke during fire season. Facts below are from each maker's own page.

Airthings View Plus

$329.99 list price

Airthings lists a PM2.5 sensor (a laser optical particle counter, 0 to 1,000 µg/m³), plus radon, CO2, VOCs, humidity, temperature and air pressure. It does not measure PM10. Runs on 6 AA batteries or USB-C and connects over Wi-Fi.

See Airthings View Plus on Amazon →

IQAir HealthPro Plus

$1199.99 list price

A large-room purifier. IQAir says its HyperHEPA filter captures ultrafine particles down to 0.003 microns. IQAir now sells it as the HealthPro Plus XE. IQAir publishes no AHAM CADR.

See IQAir HealthPro Plus on Amazon →

Filterbuy MERV 13 Filters

Check current price

EPA suggests a MERV 13 HVAC filter for smoke season, if your system can take it. Filterbuy makes MERV 13 filters in 1, 2 and 4 inch depths. Filterbuy also notes that MERV 13 does not remove odors or gases. This button opens the 20x25x4 size, 2-pack; check your own filter size first.

See Filterbuy MERV 13 on Amazon →

For full air purifier picks, see our guide to the best air purifiers for smoke and our roundup of the best air quality monitors.

Common Questions

What AQI is dangerous for wildfire smoke?

EPA says AQI values above 100 are unhealthy: first for sensitive groups, then for everyone as the number climbs. For fine particles, EPA's sensitive groups are people with heart or lung disease, older adults, and children, including teens. During smoke, EPA adds pregnant people. At 301 and higher, EPA's advice is that everyone avoid all physical activity outdoors.

Should I run my HVAC during wildfire smoke?

EPA says yes, if it has a good filter. Set it to recirculate, or close the fresh air intake. Set the fan to 'On' instead of 'Auto' so air keeps moving through the filter. EPA suggests a MERV 13 filter or as high as your system allows, and changing it more often during heavy smoke.

Do N95 masks work for wildfire smoke?

EPA says that when worn properly, N95 respirators will significantly reduce your exposure to smoke particles. Pick one with 'NIOSH' and 'N95' printed on it, with two straps that go around your head, and check for a tight seal. AirNow says cloth masks will not protect you from smoke. EPA says that if you have heart or lung problems or are pregnant, ask your doctor before using a respirator.

How long does wildfire smoke stay in the air?

It depends on the fire and the weather. AirNow says smoke can travel a long distance from a fire, and smoke levels can change a lot during the day. EPA says that when the air gets better, even for a short time, you can open windows and air out your home. Check AirNow's Fire and Smoke Map rather than guessing.

What is PM2.5 and why does it matter?

PM2.5 means fine particles, generally 2.5 micrometers and smaller. EPA says a human hair is about 30 times wider than the largest of them. They can get deep into the lungs, and some may get into the blood. EPA says the biggest health threat from smoke is from fine particles.

This guide repeats what EPA and AirNow publish. It is not medical advice. If you have a health condition, ask your doctor what to do during smoke.

Sources and last review

Specifications on this page are taken from the documents below, on the dates shown. We do not physically test products; read our methodology. Page last reviewed .

Affiliate Disclosure: Some links on this page are Amazon affiliate links and may earn us a commission at no extra cost to you. As an Amazon Associate I earn from qualifying purchases. Our picks are based on the makers' published figures, not commission rates. Full disclosure.