Living With It
The filter bank handles the air you invite in. These three things handle everything else — and they’re what make the budget tier viable.
Don’t Skip: Indoor Recirculation Filtration
The intake filter bank handles the outdoor air you intentionally bring in. Recirculation filtration provides a second line of defense against smoke that enters through the envelope or is generated indoors — and it can substantially improve performance when the intake stage has limited efficiency.
- If you have forced-air HVAC: upgrade the return-side filter to the highest MERV your blower can handle (check static pressure — many systems handle MERV-13 fine, some need a deeper 4” media cabinet).
- Either way: run portable HEPA purifiers (or DIY box-fan + MERV-13 units, including the well-documented Corsi-Rosenthal box) in bedrooms and main living areas during events. Recirculating filtration gets multiple passes at the same air, so even MERV-13 performs well here.
Seal the Envelope
Every unfiltered leak undermines the system. Before fire season:
- Air-seal the obvious offenders: attic hatches, rim joists, plumbing/electrical penetrations, door weatherstripping.
- If your HVAC ducts run through unconditioned space, seal them (mastic, or Aeroseal professionally).
You don’t need Passive House airtightness — you need to shrink the uncontrolled leakage enough that your filtered ventilation dominates the air exchange.
Commission the System
Before fire season, test the system in both normal and smoke modes. Ideally, measure supply and exhaust airflow in each mode and measure the pressure drop across the assembled filter bank. Smoke mode should leave the unit within its manufacturer's operating range and should not create more building depressurization than the equipment and building can safely tolerate.
Then compare indoor PM2.5 with the filter bank bypassed and engaged under similar outdoor conditions. A good result is a substantial reduction in indoor PM2.5 without unacceptable loss of ventilation airflow. These measurements are more useful than relying on the filter label alone.
Operating Playbook
Stock spare filters and carbon. Test the dampers. Verify sensor connectivity.
System in filtered mode (automatic or manual), with outdoor airflow reduced as appropriate for the unit and building. The goal is to minimize smoke entry while still providing appropriate filtered outdoor-air ventilation. Run indoor recirculation filters. Watch indoor PM2.5 to confirm the filtration is working. Watch CO2 as a ventilation indicator; if it rises substantially above your normal occupied level, increase filtered outdoor airflow as needed rather than treating 1,000–1,200 ppm as a hard health cutoff.
Watch VOC readings only as a trend indicator, not as a reliable carbon-breakthrough detector; consumer VOC sensors do not identify all wildfire gases and can respond to unrelated indoor sources. Replace carbon and any impregnated media according to a conservative schedule based on smoke exposure and the media manufacturer's guidance. Replace the pre-filter if it loads enough to affect airflow or pressure drop.
System back to normal mode (the bypass saves your expensive filters for next time). Note filter condition for next season’s stocking.
Questions or improvements? Email contact@firebreakhome.com — and if this guide saved you time, sharing it helps more than anything.