Every year around this time the Sacramento Valley picks up that particular haze, the light turns orange in the afternoon, and the air quality index becomes something people actually check before letting the kids outside. Closing the windows is the obvious first move. What most homeowners in Fair Oaks, Carmichael and Orangevale do not realize is that once the windows are shut, the single biggest factor in what you breathe is your heating and air conditioning system.

Your HVAC system moves the entire volume of air in your house through a filter several times an hour. That makes it either the best air cleaner you own, or the thing quietly distributing smoke through every room.

What Wildfire Smoke Actually Is, and Why It Gets Inside

Smoke is not mostly ash. The part that matters is PM2.5, particles under 2.5 microns, roughly one-thirtieth the width of a human hair. They are small enough to stay suspended for days, small enough to slip through the gaps around a closed window, and small enough to travel deep into the lungs.

Because they are so small, they also pass straight through the cheap fiberglass filter most systems ship with. A filter that stops dust and pet hair does essentially nothing about smoke. This is the gap that catches people out: the system is running, the filter is new, and the house still smells like a campfire.

Step One: The Right Filter, Not Just A Clean One

Filters carry a MERV rating for how fine a particle they capture. For smoke you want MERV 13 if your equipment can handle it, because that is where filtration starts meaningfully capturing PM2.5.

The caution is real, though. A denser filter restricts airflow, and a system designed around a thin filter can struggle, longer run times, a colder coil, and in the worst cases a frozen evaporator or a stressed blower motor. Whether your system can take a MERV 13 depends on its blower and duct design, which is a two-minute question for a technician and an expensive guess to make alone. Our guide to choosing the right air filter covers the sizing basics, and during smoke season the honest rule is: check it monthly, not seasonally. A filter loaded with smoke particles is a restriction, and it will not tell you it is full.

Step Two: Run The Fan, Do Not Just Run The AC

Most thermostats let you set the fan to ON rather than AUTO. On AUTO the fan runs only while the system is heating or cooling, so on a mild September day the air might sit still for hours. Switching to ON keeps air circulating through the filter continuously.

It costs a little in electricity and it is the single most effective free thing you can do on a smoke day. Set it back to AUTO when the air clears.

Step Three: Stop Pulling Smoke In

Whole house fans are wonderful in a Sacramento summer and exactly the wrong tool during smoke. They work by pulling outside air through the house, so on a bad air day they are an intake for everything you are trying to avoid, a detail worth knowing if you read our whole house fan comparison earlier this summer and have been enjoying yours. Keep it off until the AQI drops.

The same logic applies to the leaks you cannot see. Ductwork that runs through an attic is sitting in the hottest, smokiest air in the building, and a leaking return duct pulls that air directly into the airstream. Homeowners who did everything right and still smelled smoke very often have a duct problem, not a filter problem, the signs are in our post on ductwork leaking air into the attic, and sealing it is worth doing for your utility bill regardless of fire season.

Step Four: When A Filter Is Not Enough

For households with asthma, COPD, young children or anyone recovering from illness, filtration alone sometimes does not get there. A whole-home air purifier installed in the ductwork treats every cubic foot of air the system moves, without the noise and coverage limits of a portable unit in one room. The iWave air purifier we install works alongside your filter rather than replacing it, and it runs whenever your system runs.

It is not a magic box. Nothing eliminates smoke entirely while it is outside your walls. But the combination of a good filter, continuous circulation, sealed ducts and in-duct purification is the difference between a house that feels like refuge and a house that feels like the driveway.

What To Do After The Smoke Clears

Two things, both easy to forget.

Change the filter, even if it is early. It has been working harder than usual and it is full of the exact particles you paid it to catch.

Then get the system looked at before heating season. A summer of long run times followed by a stretch of heavy filtration is precisely the sequence that shows up as a failure in November. Our HVAC maintenance plan covers the fall visit, and if you would rather just have it inspected once, that is fine too.

Smoke season and heating season overlap in the Sacramento region by about six weeks. The homes that get through both comfortably are the ones where somebody looked at the equipment in between.

Breathing something you would rather not? Contact Absolute Comfort or call (916) 224-7159. We serve Fair Oaks, Carmichael, Citrus Heights, Orangevale, Rancho Cordova, Folsom, Roseville and the surrounding Sacramento area.