When wildfire smoke drifts into Lamorinda, Diablo Valley, or East County, it can make your home feel less like a refuge and more like the outdoors. You want your bedrooms to be restful, your living room comfortable, and your family protected without a costly remodel. In this guide, you’ll learn simple, proven steps to cut indoor smoke, choose the right filters, and run your systems the smart way. Let’s dive in.
Why PM2.5 matters
Wildfire smoke contains a mix of gases and tiny particles. The main concern inside homes is PM2.5, which is small enough to travel deep into your lungs. Short bursts of high PM2.5 can trigger breathing issues and stress the heart, especially for children, older adults, pregnant people, and anyone with asthma or heart and lung conditions.
During smoke season, the goal is straightforward: reduce indoor PM2.5 and limit outdoor exposure when air quality is poor. You can do that by keeping smoky air out and filtering the air indoors.
Keep smoke out and filter air
Central HVAC filtration
If you have a central forced air system or heat pump, use the highest MERV filter your system can handle. Many experts recommend targeting MERV 13 or higher when compatible because it removes more PM2.5 from recirculated air. Thicker pleated filters, such as 4 to 5 inches, can help reduce pressure drop while improving filtration.
Set your HVAC fan to ON during smoke events so air keeps moving through the filter. Plan to replace filters more often during smoke season since they load faster.
If your blower struggles with high-MERV filters or your cabinet is too small, talk with a qualified HVAC professional. Options include an in-duct filter box or a whole-home high-efficiency filter unit.
Portable HEPA air cleaners
A good portable HEPA purifier can deliver a big drop in PM2.5 in the rooms where you spend the most time. Choose units with a Clean Air Delivery Rate (CADR) that matches your room size. Place them in bedrooms and your main living area, and run them on higher settings during smoke events. They work best with windows and doors closed.
On a tighter budget, a properly built Corsi-Rosenthal box made from a box fan and multiple MERV 13 filters is a strong DIY alternative.
Seal the envelope
Reducing uncontrolled leaks makes it harder for smoke to sneak inside. Add weather-stripping and door sweeps, and seal exterior gaps around windows and doors with caulk. Close fireplace dampers and seal unused chimneys. If you have obvious window leaks, a temporary plastic film kit can help during the season.
Be mindful that over-sealing without managing indoor sources can raise humidity and indoor pollutants from cooking or cleaning. During smoke events, you want to reduce infiltration while still using your stove hood or bathroom fans when needed.
Smart ventilation control
Avoid bringing smoky outdoor air inside. If you have systems that pull in outdoor air, such as ERVs, HRVs, or whole-house fans, switch to recirculation modes where possible and close outside air dampers during smoke events. For many forced-air systems, set the system to recirculate with the fan ON and the outdoor intake closed.
If your ERV or HRV has a smoke or recirculation mode, use it per the manual. You can use outdoor AQI information to guide when to close up and when to resume normal ventilation.
Create a clean room
When smoke lingers for days, setting up a designated clean room can improve sleep and comfort.
- Choose an interior bedroom with few windows and a door.
- Run a HEPA air cleaner sized to the room.
- Keep the central fan ON if possible so filtered supply air reaches the room.
- Seal door gaps with weather-stripping or a door sweep. A towel at the threshold helps for a quick fix.
- Avoid indoor pollution sources in this room, such as candles or smoking.
A well set up clean room will usually show a clear drop in PM2.5 compared to the rest of the house.
Size and run your cleaners
Quick CADR math
Use CADR to match a purifier to the room:
- Find room volume: area in square feet × ceiling height in feet.
- Choose a target air changes per hour. For wildfire smoke, aim for about 4 to 6 ACH in sleeping spaces.
- Required CADR in cfm ≈ (room volume × ACH) ÷ 60.
Example: A 150 sq ft bedroom with 8 ft ceilings equals 1,200 cubic feet. For 5 ACH, CADR ≈ (1,200 × 5) ÷ 60 = 100 cfm. Pick a HEPA unit that meets or exceeds that.
Daily operation tips
- Keep windows and exterior doors closed when filtration is running.
- Run portable purifiers on higher speeds when smoke is heavy, then drop to a quieter setting for sleep if needed.
- Use your central fan continuously during smoke events if your system allows it without cycling the compressor.
- Skip whole-house fans or window cooling when outdoor air is smoky.
Maintenance schedule
- Central HVAC filters: check every 1 to 3 months during smoke season, and more often during heavy events.
- Portable HEPA units: follow the manufacturer’s guidance. Clean or replace pre-filters when they look dusty.
- DIY filter boxes: check daily during heavy smoke. Replace filters when visibly dirty or airflow drops.
Track AQI and indoor PM
Use outdoor AQI updates and community sensors to decide when to close up and run filtration. An indoor PM sensor helps you see if your efforts are working. When your systems are set up correctly, indoor PM2.5 should be substantially lower than outdoors during smoke events.
Priority plan for Contra Costa homes
Immediate, low-cost actions
- Close windows and doors. Set HVAC to recirculate with the fan ON.
- Run portable HEPA purifiers in bedrooms and your main living area.
- Create a clean room for sleeping with a properly sized HEPA unit and basic door sealing.
- If you must go outside during heavy smoke, consider an N95 or KN95 mask for added protection.
Moderate cost, moderate effort
- Upgrade your central filter to the highest MERV your system supports. Many homes can target MERV 13 when compatible, especially with a thicker pleated filter to reduce pressure drop.
- Add weather-stripping and door sweeps to cut infiltration.
- Purchase an indoor PM2.5 monitor to verify results and adjust your plan.
Higher cost, longer-term
- Install a whole-house high-efficiency filter or in-duct HEPA unit after an HVAC consultation.
- Improve air sealing and windows during planned renovations.
- Add dedicated mechanical ventilation with high-efficiency filtration and controllable outside-air dampers that you can adjust during smoke events.
- Consider upgrading older blower motors that cannot support higher-MERV filters.
Local context and resources
Contra Costa homes vary widely, from older properties with leaky envelopes to newer builds with heat pumps or mini-splits. Older ducts and gaps can increase infiltration, which makes filtration work harder. If your home uses mini-splits without a central recirculation option, prioritize portable HEPA units and careful room sealing.
During regional wildfire smoke, local agencies share near-real-time PM2.5 and AQI updates and may open community clean-air centers. These can be a key fallback if home upgrades are not possible. County public health and emergency services also issue advisories tailored to Contra Costa neighborhoods.
Make it part of your home plan
A cleaner indoor air plan supports daily comfort and can be a smart home improvement. Portable HEPA units, a central filter upgrade, and simple weather-stripping are practical steps you can take before the next smoke event. If you are preparing to sell, these upgrades can improve how your home feels during showings, and they show buyers your home is cared for. If you are buying, understanding HVAC compatibility and envelope condition helps you plan your first season.
If you want a plan tailored to your household, neighborhood, and HVAC setup, let’s connect. Reach out to Unknown Company for a personal consultation. Let’s talk about your home. Schedule a personal consultation.
FAQs
What is PM2.5 and why it matters during Contra Costa smoke season
- PM2.5 are fine particles from wildfire smoke that reach deep into lungs; during smoke events you should reduce indoor PM2.5 to lower short-term health risks.
How to choose the right HEPA purifier size for a bedroom
- Calculate CADR using room volume and target 4 to 6 air changes per hour, then pick a unit with a smoke or dust CADR that meets or exceeds the result.
Can my central HVAC handle a MERV 13 filter
- Many systems can, especially with thicker pleated filters that lower pressure drop, but confirm compatibility and consult an HVAC pro if your blower struggles.
What is a clean room and how to set one up at home
- Select an interior bedroom, seal door gaps, close windows, and run a properly sized HEPA purifier to keep PM2.5 lower for rest and sleep.
Should I run whole-house fans or open windows when it is smoky outside
- No; avoid bringing smoky air indoors, keep windows shut, and use recirculation with filtration until outdoor AQI improves.
