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Filterbuy.com’s research roundup and practical guidance for Northern & Southern California
California burns for a mix of reasons: long dry seasons, wind events, dry vegetation, and human activity. Understanding why fires start and spread in different parts of the state helps you plan, especially for keeping indoor air healthier during smoke events.
California’s climate is dry for much of the year. Vegetation dries out, then a spark, caused by human or lightning, can start a fire that spreads fast in the wind. California’s highly seasonal rainfall and warm, dry periods create months of elevated risk each year.
Most ignitions in the U.S. are human caused (campfires, debris burning, equipment, vehicles, fireworks, arson). National Interagency Fire Center data show human causes account for roughly 85% of wildfires nationally.
A smaller share comes from utility equipment, but those fires can be especially destructive. The California LAO reports utility powerlines caused at least 8 of the 20 most destructive fires in state history.
Wildfire smoke slips indoors through small gaps around windows and doors, leaky weather-stripping, fireplace dampers left open, bathroom and kitchen exhaust vents, window A/C sleeves, and other cracks in the building shell.
During smoke events, close windows and doors, minimize exhaust fan use, shut the fireplace damper, and seal obvious gaps with painter’s tape or towels.
Setting up one “clean room” with tighter sealing plus an air cleaner gives you a low-smoke refuge until outdoor air improves.
Your central HVAC can help if you upgrade the return filter and keep air circulating through it.
Filterbuy offers precise-fit MERV 11–13 pleated filters (standard and custom sizes) and an Odor Eliminator option with activated carbon for homes that also notice lingering smells.
A portable true-HEPA air cleaner reduces the particles you actually breathe in the rooms you use most.
Size it by CADR. A simple rule is smoke CADR should be equal to two-thirds of the room’s square footage. Place the unit with a clear path for intake and outlet, run it on high for the first hour to “catch up,” then leave it on Auto or low so it can work all day.
For musty odors, use a unit or prefilter with activated carbon as well.
Use a high-efficiency HVAC filter and keep air recirculating. The EPA advises using MERV 13 or the highest your system can handle and setting your system to recirculate during smoke events.
Choose a snug, exact-size Filterbuy filter so there are no bypass leaks, add Odor Eliminator if smells linger, and turn on Auto Delivery so a fresh filter arrives before fire weather. If you also want room-by-room help, a DIY box-fan purifier built with a MERV 13 filter is an EPA-studied, low-cost add-on.
Most starts are human-caused (equipment, vehicles, debris burning, fireworks, arson). Lightning also starts fires, especially in Northern California during dry-lightning events.
Santa Ana winds bring hot, very dry air and strong gusts. Humidity drops and flames move quickly.
Through gaps around doors and windows, leaky weather-stripping, fireplace dampers, bathroom/kitchen vents, and window A/C sleeves.
Yes—set the fan to On or Circulate so air passes through the filter. Close outside-air intakes and keep windows shut.
Use MERV 13 if your system can handle it. If not, use the highest your blower allows (often MERV 11). Replace sooner after heavy smoke.
No. Carbon reduces odors and some gases. MERV/HEPA media capture the smoke particles (PM2.5).
Pick a true-HEPA model with smoke CADR ≈ two-thirds of the room’s square footage (e.g., 300 ft² → ~200 CADR). Run it continuously.
Yes. Seal one room as best you can and run a true-HEPA purifier inside. Use it as a low-smoke space during bad air.
Avoid it. It pulls outdoor air in and can bring smoke indoors.
No. Ozone is a lung irritant. Use true-HEPA; if an ionizer is included, keep it off unless the unit is certified to strict ozone limits.
Check the unit manual or ask an HVAC technician. Signs of trouble include weak airflow, new noise, or rooms feeling stuffy. If so, use MERV 11.
Inspect right after conditions improve. If the filter looks dark or smells smoky, replace it now. Otherwise, change earlier than your normal schedule.
