Indoor Air Quality During Wildfire Smoke: A Pacific Northwest Homeowner's Guide

For Portland-metro and Pacific Northwest homeowners, smoke season has become as routine as November rain. What was once an occasional bad week has shifted into something more persistent — stretches of days when the air outside carries fine particles from fires burning hundreds of miles away, sometimes much closer. The orange-tinged sky and the smell of smoke settling into the valley are familiar now. What matters for your health is what happens inside your home.

Who Needs to Be Most Careful

Not everyone is affected equally. Children's developing lungs and faster breathing rates mean they take in more particles per body weight than adults. Older adults face elevated risk from the cumulative effects of age on heart and lung function. Anyone with asthma, chronic obstructive pulmonary disease, heart disease, or diabetes should treat a serious smoke event as a genuine health concern, not a minor inconvenience. Pregnant people are also in a higher-risk category.

If your household includes anyone in these groups, the steps below are worth taking seriously even when conditions seem only moderately smoky. During smoke events, the EPA guidance on wildfires and indoor air is a useful reference.

Creating a Clean-Air Space

You do not need to treat your entire home as a hermetically sealed space. A more practical approach is to identify one room — a bedroom works well because it is smaller and people spend long hours there — where vulnerable household members can shelter during peak smoke hours.

Close windows and doors throughout the home. Use weatherstripping or a rolled towel along door gaps in older homes. Close the fireplace damper — it is a significant pathway for outdoor air. Run a portable air cleaner with a high-efficiency particulate filter continuously in your clean-air room. If you have a central heating or cooling system, set it to recirculate indoor air rather than drawing in outdoor air.

The goal is a meaningful reduction in particle concentration compared to outside — not zero, which is not achievable in a lived-in home.

Your HVAC System and Filters

The filter in your forced-air heating and cooling system is your first defense. Filters are rated on a scale measuring how efficiently they capture particles of different sizes. Standard filters designed to protect equipment from large dust particles do very little against the fine particles in wildfire smoke. A filter rated toward the higher end of the residential range captures a far larger fraction of what matters most.

Before smoke season, check what filter your system uses and consider moving to a higher-rated option. Verify your equipment can handle the added airflow resistance — a system not designed for high-resistance filtration can be strained. An HVAC technician can tell you the highest rating your specific equipment can safely use.

During a smoke event, set your system fan to run continuously so air keeps moving through the filter even when the thermostat is satisfied. If your system has a fresh-air intake, close or disable it until conditions improve.

Portable Air Cleaners and DIY Options

Portable air cleaners fill an important gap, particularly for households without central forced air or for anyone wanting to protect a specific room. A unit with a true high-efficiency particulate filter, sized generously for the room, can substantially reduce indoor particle concentrations within an hour or two. During heavy smoke, running it at a higher speed to turn the air over more frequently is worthwhile.

A do-it-yourself option that has been tested by air quality researchers involves securing a high-rated furnace filter to the intake side of a box fan. Effectiveness depends on a good seal between the filter and the fan frame, and on using a filter with a sufficient particle-capture rating. It is not as refined as a purpose-built unit, but for households caught unprepared during an event, it is a meaningful step.

Sealing Gaps and Managing Ventilation

Older homes throughout the Pacific Northwest often have noticeable air leakage. During a smoke event, that leakage works against you. Temporary sealing — towels along door gaps, tape over gaps in older windows, a draft stopper at an exterior door — reduces how much smoky air infiltrates between filtration cycles. The effort does not need to be permanent, just effective for the days conditions are bad.

When outdoor air improves — often in the early morning hours in valley locations as marine air pushes inland overnight — that is a good window to ventilate and let air cleaners work from a lower starting concentration before you close up again.

Monitoring Air Quality Before You Ventilate

Pacific Northwest air quality can shift quickly. A morning with acceptable readings can deteriorate by afternoon as smoke drifts in from the south or east, then improve overnight. Checking the air quality index before opening windows or sending children outside is a habit worth building during smoke season.

The air quality index translates particulate measurements into a single number and color band. At lower readings, brief outdoor activity and limited ventilation are generally fine for healthy adults. As readings climb, the case for staying sealed and relying on indoor filtration strengthens. At the upper ranges — which do occur in the Willamette Valley and other Pacific Northwest basins during severe fire years — outdoor air becomes harmful for everyone, not only those in vulnerable groups. On those days, a well-filtered indoor space is where you want to be. Check current conditions before ventilating at https://www.airnow.gov/.