Wildfire Smoke and Cabinetry

A smoke season in Sonoma County, the Napa Valley or the Sierra foothills does not need to put a fire anywhere near a house to put its residue inside one. The U.S. Environmental Protection Agency’s guidance on wildfires and indoor air quality is written for exactly that case — smoke that enters through the building envelope and the HVAC intake — and its advice after the smoke clears begins with the observation that you may need to clean up ash or other debris left behind by the fire, and that ash deposited on surfaces indoors can become airborne again when it is cleaned. The California Department of Public Health says the same thing from the other direction: ash and debris can be blown into homes, and the indoor cleaning routine it prescribes assumes it has been.

On cabinetry, the residue shows up in three places. Horizontal surfaces — the tops of wall cabinets, the counters, the inside of any drawer left open — collect ash and fine dust as a visible layer. Vertical faces collect a finer film that is often invisible until a cloth comes away grey, and that film is heaviest near the range, where it mixes with the cooking residue already there. And the interiors of the boxes collect whatever the air carried through the gaps around doors and drawer fronts, which is why a kitchen that looks clean can still smell of smoke a week after the windows were opened.

The finish matters to how all of this cleans. A catalysed film — conversion varnish or two-component polyurethane, the finishes custom cabinetry is sprayed with in the shop — presents a smooth, closed surface that residue sits on rather than in. The Wood Handbook’s discussion of moisture-excluding effectiveness is about water vapour rather than smoke, but its central point carries: a film finish is a barrier that slows what passes through it. The cabinetmaker’s experience is consistent with that: finished faces and interiors wipe clean; raw wood, unfinished cabinet backs and open end grain hold odour. That is one more reason every face, edge and interior is finished before cabinetry leaves the Rocklin shop.

The EPA’s filtration advice is specific enough to act on. Choose a high-efficiency HVAC filter, such as one with a Minimum Efficiency Reporting Value of 13, or as high a rating as the system fan and filter slot can accommodate; make sure the filter fits snugly so air does not leak around it; set the system to recirculate, or close the outdoor intake damper, so the house is not drawing smoke in; and plan to replace the filter more often than the manufacturer recommends while the smoke lasts. For rooms where people spend the most time, the agency recommends a portable air cleaner sized to the room, placed where people are, and one that does not produce ozone.

The agency’s separate guide to air cleaners explains why the filter rating and the run time both matter. Filters rated MERV 13 and above are required to demonstrate a minimum removal efficiency, and a central system normally runs only when heating or cooling is called for — usually less than a quarter of the time in the heating and cooling seasons — so a MERV 13 filter in a system that is not running is filtering nothing. Running the fan continuously during a smoke event costs electricity and, the guide notes, can make humidity control less reliable in the cooling season; it is also the only way the filter sees the air it is meant to clean.

For the cabinetry the sequence is what counts. Residue is still settling for as long as the air carries it, so a kitchen wiped down on the first clear morning is grey again by the weekend. Let the system run on the upgraded filter, let the portable cleaner work in the kitchen, and clean the cabinets once — properly — when the air has cleared and the surfaces have stopped loading. The EPA’s position on ducts belongs here too: it recommends air ducts be cleaned only as needed, not as a routine response to a smoke event. A filter changed on time is where the particles belong.

A kitchen in Santa Rosa, Healdsburg, Calistoga or Auburn can expect smoky weeks in most years whether or not a fire is near, and the cumulative effect on cabinetry is of many light clean-ups rather than one heavy one. That changes the emphasis. The agencies’ method — damp cloth, HEPA vacuum, little water — is the right one for every clean-up, but the thing that protects the finish over a decade of them is restraint: dry dusting between smoke events, as the manufacturers recommend, and the wet routine reserved for the weeks that need it. A finish washed daily through five fire seasons is not better protected than one dusted dry and washed when the air clears; it is simply wetter, more often, at its edges.

The filtration side can be set up once. A system that takes a MERV 13 filter, a stock of them on the shelf, a portable HEPA unit for the kitchen and the habit of switching to recirculate when the air turns are the EPA’s recommendations, and air that was filtered before it reached the kitchen leaves less on the doors.

And the construction side is settled before the first smoke season: every face, edge and interior finished, so there is no raw wood for odour to lodge in; doors and drawer fronts that close well against their openings, so less of the room air enters the boxes; and a finish chosen for chemical and abrasion resistance rather than ease of touch-up. Those are the ordinary decisions in the cabinet construction guide; a kitchen in the Mayacamas just does not get to skip any of them.