How to Run Your HVAC During Wildfire Smoke in Camas, WA

Wildfire smoke can sweep into southwest Washington with little warning, and it moves differently through a home than typical outdoor dust or pollen. Many Camas homes rely on heat pumps, furnaces, or ductless mini-splits for year-round comfort, and those systems can either help or hinder indoor air quality when smoke drifts in. The goal is to keep fine particulate (PM2.5) out while safely circulating and filtering the air you already have. That comes down to filter selection, system settings, and how fresh air enters your home. Here is a practical, mechanics-first guide to operating common residential HVAC equipment when the air outside turns smoky.

1. How Wildfire Smoke Interacts With Forced-Air Systems

Forced-air systems recirculate indoor air through a return plenum, across a filter, and back to rooms through supply registers. PM2.5 from wildfire smoke is tiny, so a higher-rated filter (often MERV 13, which the blower can handle it) captures more of it. However, higher MERV ratings also increase pressure drop, which can strain undersized blowers or starve the evaporator coil of airflow. Before you jump to a thicker or denser filter, have the system’s airflow capability checked; local resources for Camas, WA HVAC services can evaluate static pressure and advise on media that improves filtration without hurting performance.

Even the best filter underperforms if air bypasses it. Gaps around a 1-inch filter rack, a warped filter frame, or a return grille that doesn’t seat tightly let smoky air sidestep the media. In older homes, leaky return ducts in attics or crawlspaces can also draw in smoky air. Inspect that the filter fits snugly, the arrow faces the airflow, and any fresh-air takeoff on the return side is dampered shut during smoke events. If you can access the return plenum, look for unsealed seams and use mastic or UL-181 tape to close obvious leaks.

2. Central Furnaces and Heat Pumps: Filters, Fan Mode, and Airflow

Many Camas homes use a central heat pump or furnace with a 1-inch filter slot. A MERV 13, 1-inch filter can be restrictive for some blowers. A 3–5-inch media cabinet (MERV 11–13) offers more surface area with lower pressure drop. Pair that with running the indoor fan in On or Circulate mode during smoke events so the same air passes the filter multiple times each hour. Expect a small energy bump from continuous fan use. On the plus side, when cooling is active, the evaporator coil and condensate drain help remove both heat and some particle-laden moisture, which can slightly aid IAQ as long as the filter is clean.

Watch out for airflow red flags: rooms suddenly feel stuffy, the supply air is weak, or a heat pump runs long and ices over. Those symptoms can worsen with a clogged or overly dense filter. If your thermostat allows it, a modest increase in blower speed can offset the added filter resistance, especially on systems with ECM motors. Confirm that any intentional outside air damper to the return is closed. During heavy smoke, keep windows shut and avoid running the range hood or bath fans continuously; they exhaust indoor air and can pull smoky air in through leaks.

3. Ductless Mini-Splits and Window Units: Reducing Infiltration and Cleaning

Ductless indoor heads typically rely on washable mesh prefilters and, in some models, thin charcoal inserts. These are not HEPA-grade. Clean the prefilters every few days during smoke events to keep airflow strong and prevent the coils from fouling with soot. If the home also uses window ACs in bedrooms, shut any outside-air slider on the unit and seal the accordion side panels with foam or tape to reduce infiltration. Run the fan on Low or Medium so the built-in screen has longer contact time with recirculated air, but remember that those screens catch only larger particles.

Because mini-split filtration is limited, a portable HEPA unit in key rooms can make a noticeable difference. Place it away from the mini-split head so both devices don’t fight for the same airstream. Avoid ozone-generating “purifiers,” which introduce a lung irritant and do not remove particulates. In a small ranch home with one ductless head in the living area and two window ACs, the routine might be: seal the window units, run the mini-split in recirculate, add a HEPA purifier to each bedroom, and keep doors mostly closed to concentrate filtration where people sleep.

4. ERVs, HRVs, and Fresh-Air Intakes: When to Pause Ventilation

Energy recovery ventilators (ERVs) and heat recovery ventilators (HRVs) bring outside air in by design. During heavy smoke, switch them off or put them in standby if your controller allows it. If your forced-air system has a fresh-air duct tied to the return, close its motorized damper. Limit continuous use of exhaust fans; long runs of a bath fan or a powerful range hood can create negative pressure that draws smoky air through cracks around doors, recessed lights, and rim joists. Airtight homes are less affected, but most homes leak at least some air under pressure.

There is a trade-off. Pausing ventilation can raise indoor CO2 and humidity. Manage this by doing short, timed ventilation only if outdoor AQI improves temporarily, and by using dehumidification via your heat pump or portable unit if indoor humidity creeps up. An inexpensive IAQ monitor that tracks PM2.5 and CO2 helps you choose when to unpause ventilation. In practice, a family with an ERV might set it to standby during peak smoke, run bathroom fans only for quick moisture control, and wait to reintroduce outdoor air until the AQI falls to a healthier range.

5. After the Smoke Clears: Filter Changes and System Checkups

Smoke loads filters fast. Replace the furnace or air handler filter after the event, even if it is ahead of your normal schedule. If your system ran for days in smoky air, have a technician check the blower wheel and evaporator coil for soot buildup that can raise static pressure and reduce heat transfer. A quick visual inspection of the outdoor coil also helps if ash settled around the unit. If frequent smoke is likely each summer, ask about a deeper media cabinet, a well-sealed return, and confirming system static pressure with a manometer so higher-MERV filtration stays within safe blower limits.

Smoke season is unpredictable, but your response does not have to be improvised. Close outside air paths, recirculate and filter the air you already have, and choose media that captures PM2.5 without starving airflow. Keep spare high-quality filters on hand, plus foam or tape to seal window units. If you own an ERV or HRV, plan ahead for when to pause and when to resume fresh air. With a few setting changes and some routine post-event maintenance, the same HVAC equipment you rely on for comfort can also serve as a practical tool for cleaner indoor air when the skies turn hazy.