You keep wildfire smoke out of a Palouse home by combining three things: a properly sealed envelope, a MERV 13 or better filter in your HVAC system, and a portable HEPA unit in the room where people actually spend time. Any one of those alone isn't enough during a bad August week.
What actually is wildfire smoke, and why is it hard to filter?
Wildfire smoke is a mix of water vapor, larger particulates, and — the part that matters — fine particulate matter called PM2.5. Those particles are 2.5 microns or smaller, which is small enough to pass through most standard furnace filters and small enough to reach deep into lung tissue. AQI readings on smoky days measure exactly this particulate load.
Because PM2.5 is so small, a MERV 8 filter — the kind most homes ship with — captures very little of it. You need MERV 13 at minimum for meaningful smoke reduction, and true HEPA (99.97% at 0.3 microns) if you want the particulate load in a room measurably down. The physics are simple; the trap is that the equipment has to be able to move air through the tighter filter.
When does each layer of protection matter?
- Envelope sealing: the first thing to fix. Any smoke your house takes in through leaky windows, unsealed attic hatches, or gappy dryer vents will overwhelm any filter you can buy.
- HVAC filtration: matters most when the system is actively circulating air. Setting your thermostat fan to "on" instead of "auto" during smoke events keeps the filter working continuously.
- Portable HEPA units: matter in the specific room you sleep or work in. A HEPA unit rated for your room's square footage moves air fast enough to keep local PM2.5 measurably lower than the rest of the house.
- Fresh-air intakes: if you have an ERV or HRV, know where its outdoor intake is and how to close or bypass it during smoke events. Otherwise you're actively pulling smoke inside.
Where do homeowners get it wrong?
The most common mistake is dropping a MERV 13 filter into a system that was designed for MERV 8 without checking whether the blower can handle the pressure drop. Tighter filters restrict airflow, and an undersized blower fights that restriction — reducing efficiency, straining the motor, and in some cases icing the coil. Any filter upgrade should be paired with a static-pressure check on the system.
The second mistake is buying too small a HEPA unit for the room. HEPA purifiers are rated in CADR (clean air delivery rate) and room square footage. A unit rated for 200 sq ft in a 400 sq ft open living room isn't going to move the needle. Size up.
What we've seen on the Palouse
Palouse wildfire seasons have gotten more consistent over the last decade — we now plan for smoke events every August, sometimes into September. The homes that stay livable during those weeks share a pattern: tight envelopes, quality HVAC filtration, and a portable HEPA in the primary bedroom. Older farmhouses and homes near Moscow and Pullman with original single-pane windows struggle the most. We've done a lot of MERV upgrades, ERV commissioning, and whole-house dehumidifier installs across the region — and the households that invest before the smoke arrives are the ones sleeping well when it does.
What to do next
If wildfire smoke has been an issue for your household — kids with asthma, elderly parents, anyone with a heart condition — the pre-season window (spring and early summer) is the time to fix it. We can walk through your system's filter compatibility, envelope weak spots, and portable-unit sizing in one visit. Call (208) 596-7757 or reach out through our contact form to schedule an assessment.