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Common problems

Dust or wildfire smoke indoors

Surfaces get dusty days after cleaning, you smell smoke indoors on wildfire days, or dark lines appear at carpet edges and around vents. Particles follow the same leaks heat does, so sealing and filtering work together.

What an audit checks Causes in your climate The fixes

What it usually means

Outdoor particles get in wherever air does: around doors, windows and attic openings, and through leaky ducts. Return ducts in an attic, garage or crawlspace can pull in dust and fumes and blow them through the house.
On wildfire smoke days, EPA advises keeping windows and doors closed, using the most efficient filter your system can handle (MERV 13 if it can), running a portable air cleaner and setting up a clean room.
Dark lines at carpet edges and around vents often mark places where air leaks through a gap and leaves its dust behind, like a filter.

Where it’s most common

Our climate research lists this as a common problem in these metro areas. Each guide covers what homes there need, local audit programs and rebates.

Hot and dry Phoenix · Riverside
Mixed New York City · Washington, DC · Philadelphia · Baltimore · St. Louis
Cold Minneapolis–St. Paul · Denver
Marine and mild coastal Los Angeles · San Francisco · Seattle · San Diego · Portland

Somewhere else? Find your metro guide.

Likely causes, by climate

The same symptom has different causes in Miami, Phoenix and Minneapolis. Find your climate below; the tag marks the climates where this problem is most common.

Hot and humid Florida, Texas and the Gulf Coast

Dust is the more common complaint: return-duct leaks in the attic pull in attic dust and insulation fibers, and an air handler in the garage can pull in fumes if its closet and ducts aren’t sealed.

Hot and dry the desert Southwest and inland Southern California Common here

Desert dust storms and wildfire smoke both get in through leaks. An evaporative cooler brings outdoor air in by design, so on smoky or dusty days filter its intake with MERV 13 media or switch to the AC if you have one.

Mixed the Mid-Atlantic, St. Louis and the Southeast Piedmont Common here

Wildfire smoke has reached the East in recent years, including record smoke in New York City and Washington, DC in June 2023. Older homes with leaky windows, attics and basements let it in; sealing, then MERV 13 filters and a portable air cleaner, handle most of it.

Cold the Northeast, Great Lakes, Upper Midwest and Colorado Front Range Common here

Smoke from distant wildfires now reaches the Upper Midwest and Colorado often; Minnesota set a record for air-quality alerts in 2023. Homes with an HRV or ERV bring in outdoor air all the time, so keep its filters clean and, on the worst days, set it to its lowest or recirculate setting if it has one.

Marine and mild coastal the Pacific Northwest and coastal California Common here

Wildfire smoke can reach hazardous levels in the Pacific Northwest and California. Many homes have no central system to filter through, so portable HEPA air cleaners sized for the room, a clean room and well-sealed windows and doors are the core of the plan.

Not sure which climate you’re in? Your metro guide says, and the climate zone entry explains the map builders use.

How an audit confirms it

Guessing is how people end up with new equipment that doesn’t fix the problem. These tests measure the cause. Ask for them by name when you book; each guide explains what the results mean and what to do next.

Blower door test Measures how leaky the house is and, with the fan running, shows where outdoor air and smoke get in.
Duct leakage test Finds return-duct leaks in the attic, garage or crawlspace that pull dust and fumes into the system.
Mold and humidity check An indoor air check looks at humidity, ventilation and particle sources inside the house.
Combustion safety test If you tighten a house with gas, oil or propane appliances, this test makes sure they still vent safely.

Try first (cheap or free)

Weatherstrip doors, add door sweeps and seal the attic hatch and other gaps you can see.
Use the most efficient filter your system can handle; EPA suggests MERV 13 for smoke. Ask your HVAC technician if you’re not sure your system can take one.
Run a portable HEPA air cleaner sized for the room, especially in bedrooms, and set up one clean room for smoky days.
On smoke days, keep windows closed, recirculate, and avoid adding particles indoors: frying, candles, smoking, and vacuuming without a HEPA vacuum.
Check the filter more often during smoke or dust season, because a loaded filter cuts airflow.

The fix ladder

From the cheapest step to the biggest. Work up only as far as you need to, and test again after.

Weatherstripping, door sweeps and sealing the gaps you can see Free–$
Better filters, a portable HEPA air cleaner and a clean room $
Seal the return ducts and the air handler cabinet or closet $–$$
Professional air sealing of the attic, rim joists and penetrations, guided by a blower door $$
A deeper filter cabinet that can take MERV 13, or balanced ventilation (an ERV or HRV) with filtration $$–$$$

Rough cost before rebates: $ is under about $1,000, $$ about $1,000 to $5,000, $$$ about $5,000 to $15,000, $$$$ more. Prices vary a lot by region and house, so get written quotes.

When to call a pro

Your system can’t run a MERV 13 filter without losing airflow. An HVAC contractor can add a deeper filter cabinet.
Dust or insulation fibers come out of the vents, or you smell car exhaust from an attached garage. Have the return ducts and air handler sealed.
Anyone in the home has asthma, or heart or lung disease. Ask a doctor about a plan for smoke days.

Common mistakes

Running an evaporative cooler on full with the windows shut: it needs an open window or vent to work, and it pulls smoke in.
Tightening a house with natural-draft gas appliances without a combustion safety test.

Paying for the fixes

Utility programs often pay toward audits, duct sealing, insulation and heat pumps, and some require an audit first. Your metro guide lists the programs near you, and your state’s page covers state and federal rebates.

Words worth knowing

MERV rating: A 1-to-16 rating of how well a furnace or air-handler filter catches airborne particles; higher numbers trap smaller particles.
HEPA filter: A very fine high-efficiency particulate air filter used in portable air cleaners and vacuums to trap smoke, dust and other small particles.
PM2.5 (fine particulate matter): Fine, inhalable airborne particles 2.5 microns or smaller, from smoke, cooking, candles and outdoor pollution.
Indoor air quality (IAQ): How clean and healthy the air inside a home is, affected by ventilation, humidity, combustion gases, particles, chemicals and radon.
Air sealing: Blocking the hidden gaps where air leaks in and out of a house, which cuts drafts, heating and cooling costs, and moisture problems.
Air leakage: Uncontrolled air moving in and out of a house through cracks and gaps, carrying heat, moisture and outdoor pollutants with it.
Duct leakage test: A test that pressurizes your heating and cooling ducts with a calibrated fan to measure how much air escapes through leaks.
Depressurization: When more air is being pushed out of a house than is coming in, so the inside sits at slightly lower pressure than outdoors.
HRV (heat recovery ventilator): A ventilation system that swaps stale indoor air for fresh outdoor air while transferring heat from the outgoing air to the incoming air.
ERV (energy recovery ventilator): Like an HRV, but its core also transfers some moisture between the outgoing and incoming air, which helps manage humidity.

The glossary explains every term on the site.

Common questions

What filter should I use for wildfire smoke?

EPA suggests a MERV 13 filter, or the highest rating your system can handle. Higher-rated filters can restrict airflow in some systems, so check with an HVAC technician, and add a portable HEPA air cleaner for the rooms you use most.

Why does my house get so dusty?

Outdoor dust comes in through air leaks, and leaky return ducts in an attic, garage or crawlspace can pull dust and insulation fibers into the system and blow them around the house. Sealing those leaks and then using a good filter does more than dusting more often.

Should I run my evaporative cooler on smoky days?

Sparingly. An evaporative cooler pulls in outdoor air, smoke included. Fit MERV 13 filter media to the intake if you can, or use the AC instead on the worst days.

Sources

Where each problem is common comes from our regional climate research (NOAA climate normals, EPA, PNNL, FEMA and others), cited on each metro guide. The guidance on this page follows these sources, checked October 26, 2026:

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