What Cotati and Sonoma County Homeowners Should Know About HVAC and Wildfire Smoke Season — Protecting Your Home’s Air Before, During, and After a Fire Event
If you live in Cotati, Santa Rosa, or anywhere else in Sonoma County, you already know that wildfire smoke isn’t a hypothetical — it’s a seasonal reality. And while most homeowners instinctively close their windows when the AQI spikes, very few think about what their HVAC system is actually doing during a smoke event. The short answer: if you haven’t prepared it, it may be making things worse. Here’s a clear, practical breakdown of how to protect your home’s air quality before smoke season hits, how to operate your system safely while it’s happening, and what to do afterward to make sure your ductwork isn’t holding onto what the fire left behind.
Why Your HVAC System Is at the Center of This Problem
Your heating and cooling system moves air throughout your entire home — which means it’s also the main pathway for smoke particles to travel from room to room, or to enter from outside if the system isn’t set up to handle it. Most standard residential systems are designed for comfort and energy efficiency, not air quality during a wildfire event. That gap matters a lot in a region like Sonoma County, where seasonal fires — and the smoke from fires burning hundreds of miles away — can push outdoor air quality into unhealthy or hazardous territory for days at a time.
The key variables are your filter type, your ventilation settings, and the overall condition of your ductwork. Getting those three things right — ideally before smoke season arrives — makes a real difference in what your family breathes indoors.
Before Smoke Season: What to Do Now
Upgrade Your Air Filter — But Know What You’re Buying
The single most impactful thing most homeowners can do is switch to a higher-MERV filter before fire season begins. MERV stands for Minimum Efficiency Reporting Value, and it measures how effectively a filter captures small particles. Standard filters are typically rated MERV 1–4 and do almost nothing against fine smoke particulates. For wildfire season, you want a MERV 13 filter at minimum — this is the rating most often recommended by air quality agencies for smoke events, and it’s capable of capturing the fine PM2.5 particles that cause the most health damage.
One important caveat: a higher-MERV filter creates more airflow resistance, and not every HVAC system can handle it without strain. If your system is older or was sized for low-resistance filters, jumping straight to a MERV 13 without checking with a technician can cause reduced airflow, increased wear on your blower motor, or uneven heating and cooling. When in doubt, have someone look at your system before you make the switch.
Schedule a Pre-Season Tune-Up
A fall tune-up does more than just make sure your heater is ready for winter. A technician will inspect your blower, check for any leaks in your duct system, and verify that your system is operating at the airflow and static pressure it was designed for. In an older neighborhood like Rohnert Park or parts of Santa Rosa near the Railroad Square district, aging ductwork is common — and gaps or deteriorating seals in your ducts can pull unfiltered air in from your attic or crawl space, including smoke during a fire event. Catching that before smoke season is far better than discovering it during one.
During a Smoke Event: How to Operate Your System
Set Your System to Recirculate — Not Fresh Air
This is the most misunderstood setting during a wildfire event, and it’s a gap that most competitor sites in our area don’t address clearly. Many homeowners assume that running their AC or heater during smoky conditions means pulling outside air in. Whether that’s true depends on your system.
Central HVAC systems in most residential homes recirculate indoor air by default — they don’t actively draw in outside air the way a commercial system with a dedicated fresh air intake does. If that describes your home, running your system during a smoke event is generally fine and actually helps by running air through your filter repeatedly. The key is making sure your filter is clean and rated appropriately.
However, if your home has a whole-house ventilation system, an energy recovery ventilator (ERV), or a heat recovery ventilator (HRV) — which are increasingly common in newer construction in Windsor and Sebastopol — those systems are designed to bring in outside air. During a serious smoke event, you’ll want to know how to temporarily pause the fresh air intake on those units, or have a technician show you how before you need to do it in a hurry.
Run the Fan — Even When You Don’t Need Heating or Cooling
On mild days during smoke season when you don’t need active heating or cooling, you can still run your system’s blower fan continuously in the “fan only” mode. This circulates air through your filter without engaging the heating or cooling components, which helps clean the indoor air without raising your energy bill significantly. It’s a simple step that makes a real difference over the course of a multi-day smoke event.
After a Fire Event: Don’t Skip the Follow-Up
Once the smoke clears and the AQI comes back down, most homeowners move on without thinking twice about their HVAC system. That’s a mistake — especially if the smoke event was severe or prolonged.
Fine smoke particles — particularly from structure fires, which occurred in significant numbers during the 2017 Tubbs Fire and subsequent Sonoma County events — contain compounds that are harmful even in small concentrations. These particles can accumulate inside your ductwork, on your evaporator coil, and in your air handler. They don’t disappear when the outside air clears. In some cases, especially after a nearby fire or a fire that burned homes in the area, a professional duct cleaning and system inspection is genuinely warranted, not just a precaution.
At minimum, you should replace your air filter immediately after a major smoke event, even if it was recently changed. A filter that has captured a significant load of smoke particles is compromised, and continuing to run your system through it can allow particles to pass through or restrict airflow enough to damage your equipment.
If you notice a persistent smoky smell coming from your vents after conditions clear, that’s a clear signal to have the system inspected. For more information on how ventilation and air quality systems work together in Sonoma County homes, take a look at our residential ventilation services.
What About Whole-House Air Purification?
For homeowners in Cotati, Petaluma, or anywhere in Sonoma County who are tired of improvising every fire season, a whole-house air purification system installed directly in your HVAC equipment is worth a serious look. Unlike portable air purifiers that cover one room, these systems treat all the air moving through your home’s ductwork. Options range from media air cleaners with high-MERV filtration to electronic air cleaners, UV germicidal systems, and bipolar ionization units that actively neutralize particles and pathogens.
The right choice depends on your existing system, your budget, and how much you want a set-and-forget solution versus something you actively manage. These systems can be installed during a routine service visit in most cases, and there are California and PG&E rebate programs that may apply depending on the equipment and your utility account. Check our current HVAC offers and financing options to see what’s available right now.
Frequently Asked Questions
Can I run my AC during a wildfire smoke event?
Yes, in most cases. Standard residential central AC systems recirculate indoor air rather than pulling in outside air, so running your AC helps filter your indoor air as long as you have an appropriate filter installed. Just make sure your filter is clean and rated MERV 13 or higher for smoke events.
What MERV rating do I need for wildfire smoke?
Most air quality agencies recommend MERV 13 as a minimum for capturing fine smoke particulates (PM2.5). Before upgrading, confirm your HVAC system can handle the increased airflow resistance — a technician can check this during a routine inspection.
Do I need to get my ducts cleaned after a nearby wildfire?
It depends on how close the fire was and how severe the smoke exposure was. If the fire involved structure losses nearby, or if you notice a persistent smoky smell from your vents, a professional inspection and duct cleaning is worth doing. After less severe smoke events, replacing your filter promptly is usually sufficient.
My home has an HRV or ERV — what do I do during a smoke event?
You’ll want to temporarily disable the fresh air intake on your HRV or ERV during a serious smoke event, since these systems are designed to bring in outside air. Refer to your system’s manual or ask your HVAC technician to walk you through the process before you need to do it in an emergency.
How often should I change my filter during fire season?
Check your filter at least every two to three weeks during active smoke season rather than relying on a fixed schedule. A filter loaded with smoke particles will restrict airflow and reduce your system’s effectiveness. Replace it immediately after any major smoke event, regardless of when it was last changed.
Talk to Someone Who Knows Sonoma County’s Air
Stout’s Heating & AC, Inc has been working in Santa Rosa and throughout Sonoma County since 1992. We’ve seen what wildfire season does to HVAC systems up close — and we know how to help you prepare before the smoke arrives, not scramble during it. Whether you need a pre-season tune-up, help upgrading your filtration, or a post-fire inspection, we’re a phone call away.
Contact Stout’s Heating & AC, Inc to schedule a visit or ask us about the right filtration solution for your home. We serve Cotati, Santa Rosa, Rohnert Park, Sebastopol, Petaluma, Windsor, Healdsburg, and the surrounding Sonoma County area — and we’ll give you a straight answer, not a sales pitch.