When wildfire smoke settles over the Walla Walla Valley, the most effective thing you can do is close the house up and run your HVAC blower continuously with the best filter your system can safely handle. Continuous circulation pushes indoor air through that filter over and over, which removes a large share of the fine smoke particles. If your equipment cannot handle a thicker filter, a portable air cleaner in the room you sleep in is the smarter place to spend your money.
Why does wildfire smoke get inside a closed-up house?
Wildfire smoke is made of extremely fine particles. They are small enough to drift through the same gaps that let a draft in. Older homes in College Place and Walla Walla have plenty of those gaps: original windows, doors that have settled over the decades, unsealed attic hatches, and open crawlspace vents.
We see this every late summer. A homeowner calls and says the house smells like a campfire even though nothing has been opened all day. The smoke is not coming through the walls. It is coming through leaks, and then it gets circulated by a system that was never set up to filter it.
The good news is that your HVAC system is already the best air cleaning tool in the house. It moves far more air than any portable unit can. It just needs the right filter and the right settings.
What filter should I use during smoke season?
Filters are rated by MERV. The higher the number, the smaller the particles the filter can catch. For smoke, you want a MERV 13 if your system can take one.
Here is the honest catch, and it matters. A MERV 13 filter in a one inch slot restricts airflow. Many furnaces and air handlers in older valley homes were sized around a cheap fiberglass filter. Drop a dense filter into that slot and you can starve the blower, freeze a coil, or overheat a heat exchanger. That turns an upgrade into a repair bill.
- If you have a four or five inch media cabinet, a MERV 13 media filter is usually both safe and very effective.
- If you only have a one inch slot, MERV 11 is often the practical ceiling. Check it monthly while smoke is in the air.
- Skip washable metal filters for smoke. They catch lint and hair, not fine particles.
- Never run the system with no filter at all to improve airflow. Smoke residue will coat the coil and the blower wheel.
If you are not sure what your system can handle, ask before you buy. A NATE certified technician can measure static pressure and tell you in a few minutes whether a thicker filter is safe for your specific equipment.
Should I run the fan all the time when it is smoky?
Yes. Set the thermostat fan to ON instead of AUTO while smoke is in the air. On AUTO, the blower only runs when the system is actively heating or cooling, which on a mild smoky day may be very little. On ON, air keeps moving through the filter all day long.
A variable speed blower can do this for very little money. An older single speed blower costs more to run continuously, so some homeowners run it on ON during the day and switch back to AUTO overnight. Either approach is reasonable.
One caution: continuous fan operation loads the filter faster. Look at it weekly during a smoke event rather than waiting for your normal schedule.
Does my air conditioner pull smoke in from outside?
A standard central air conditioner or heat pump does not bring outdoor air into your house. The outdoor unit moves heat, not air. Running the air conditioning on a smoky day does not make your indoor air worse, and the cooling helps you keep the windows shut, which is the whole point.
There are two exceptions worth knowing about:
- Evaporative or swamp coolers. These work by pulling a large volume of outdoor air through a wet pad. On a smoky day they bring the smoke straight in with it. If you rely on one, that is the day to shut it down and cool the house another way.
- Fresh air ventilators and outdoor air dampers. Some newer or remodeled homes have one. It should be closed during a smoke event. Most homeowners do not know whether they have one, so it is worth asking during your next service visit.
What about a ductless mini-split?
Ductless mini-splits filter the air in the room they serve, but their built-in screens are thin. They catch dust, not fine smoke particles. If you heat and cool with mini-splits, run the indoor unit fan continuously and pair it with a portable HEPA air cleaner in the rooms you spend the most time in.
Keep those mini-split filters clean. Smoke season loads them up fast, and a clogged screen costs you both comfort and efficiency.
When is a whole-home air cleaner actually worth the money?
Sometimes it is, and sometimes it is not. We would rather tell you the truth than sell you a box you do not need.
It is usually worth it when:
- Someone in the house has asthma, COPD, or serious seasonal allergies.
- Your system already has, or can accept, a deep media filter cabinet.
- Dust and pollen bother you the rest of the year too, not just during fire season. In an agricultural valley, that describes most families.
It is usually not worth it when you are only chasing a few smoky weeks a year, your ductwork leaks badly, or your equipment is near the end of its life. Sealing ducts or planning a replacement first will do far more for your air than adding an accessory to a struggling system.
If someone has already quoted you a whole-home purifier and you are not sure about it, get a second set of eyes on the quote before you sign.
What should I do after the smoke clears?
Smoke leaves residue behind. A short cleanup pass keeps it from becoming a problem all winter.
- Change the filter, even if it does not look dirty. Smoke loads a filter in ways you cannot see.
- Open the house on the first clear, cool evening and air it out.
- Rinse the outdoor unit. Ash and valley dust on the coil hurt efficiency.
- Book your furnace check before the first cold snap. It is the right time to have the blower wheel and coil inspected for buildup.
A simple plan for the next smoke event
You do not need to buy anything the day the sky turns orange. Keep a spare filter on the shelf, know what MERV rating your system can handle, and know where your thermostat fan setting lives. That covers most of it.
The homes that struggle most during smoke season in Walla Walla and College Place are usually the ones with an undersized filter slot, leaky ducts, or an aging blower. Those are worth addressing in the spring or fall, not in the middle of an emergency.
Talk it through with someone local
College Place Heating & Air Conditioning has worked on valley homes since 1949, and we have watched smoke season get longer. If you want to know what your system can actually handle before you spend a dollar, call us at (509) 525-8073. We will tell you straight, and if you already have a quote in hand from someone else, our second opinion is free with no obligation.