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When outdoor AQI reaches the hazardous range, close windows and exterior doors, switch heating or air-conditioning to recirculate, and stop outdoor-air intake if your system allows it. Run the best filtration available for the occupied room or whole home, avoid creating particles indoors, and move to another cooled or heated shelter if you cannot keep the sealed home at a safe temperature. Reopen windows or fresh-air intakes only after outdoor air improves.
What to do first when AQI is hazardous
- Seal the building. Close every window and exterior door. Check less-obvious openings such as pet doors, garage-to-house doors, and damaged window seals.
- Stop intentional outdoor-air intake. Set central heating, ventilation and air-conditioning (HVAC) equipment to recirculate. Close a fresh-air damper or outdoor-air intake if the equipment has a user-accessible control. Do not disable equipment in a way that creates a safety hazard; consult its manual or an HVAC professional when unsure.
- Start filtration. Run a portable air cleaner in the room people occupy most, or run the central fan with the highest compatible filter. Use the highest practical fan setting and keep the unit operating as continuously as conditions, noise and energy use permit.
- Stop indoor particle sources. Do not smoke or vape, burn candles or incense, use a fireplace, operate a gas or propane stove unnecessarily, spray aerosols, fry or broil food, or vacuum.
- Protect people who must go outside. A properly fitted N95 or P100 respirator is the most protective option identified by the Centers for Disease Control and Prevention (CDC). A respirator protects its wearer; it does not clean room air.
If a closed home becomes dangerously hot or cold, do not trade heat illness or hypothermia for cleaner air. The U.S. Environmental Protection Agency (EPA) advises seeking another shelter that can remain comfortable while keeping smoke out.
How wildfire smoke gets indoors
Wildfire smoke contains fine particles, including PM2.5, that can penetrate buildings through open windows, doors, leaks and outdoor-air ventilation. Indoor concentrations vary widely. EPA guidance reports that, during smoke events, indoor-to-outdoor smoke levels across homes can range from about 30% to 100%. With windows and doors closed and no portable cleaner operating, indoor PM2.5 is generally about 55%–60% of outdoor levels. Building tightness, ventilation, filter fit, fan operation, room size and the outdoor concentration all change the result.
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Random freezes, missing sound and display glitches usually trace back to one bad driver. Find and replace yours safely.Free scan · under a minuteClosing openings reduces the incoming load, but it does not remove smoke already inside. Filtration and source control are therefore needed together. Cooking, combustion and aerosols can create enough particles to overwhelm a cleaner in a closed room.
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Keep windows, doors and ventilation openings closed
When to close them
Close windows and exterior doors before smoke becomes dense indoors, preferably when local air-quality alerts indicate unhealthy or hazardous conditions. Keep them closed while outdoor air remains polluted. Short periods of cleaner outdoor air can be useful, but check a current AQI reading rather than relying on visibility or smell; smoke can contain harmful particles even when the sky looks clearer.
Managing central HVAC and room air conditioners
Set a central system to recirculate indoor air. If there is a manual fresh-air damper or outside-air control, close it during the smoke episode. Many room air conditioners recirculate by default, but a unit with a ventilation setting may draw outdoor air; turn that function off if the manual permits. Never block combustion-air or flue openings for a fuel-burning appliance, and never operate a fuel-burning generator indoors.
What to do if the home overheats
Sealing a building can reduce cooling. Watch for headache, dizziness, weakness, nausea, confusion or unusual sleepiness, especially in children, older adults and people with heart or lung disease. If you cannot maintain a safe indoor temperature with windows closed, move to a cleaner-air shelter with reliable cooling rather than opening windows into hazardous smoke.
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| Approach | Coverage | Key requirements | Main limitations |
|---|---|---|---|
| Central HVAC filter | Potentially the whole home, but only while the fan moves air | Equipment must accept the filter thickness and airflow resistance; use MERV 13 or higher when compatible | Does not clean rooms the system does not adequately circulate; poor fit allows bypass |
| Portable HEPA air cleaner | One room or zone | Size the unit for the room, place it where people spend time, and run it on the highest practical speed | Limited coverage beyond the room; replacement filters and noise require planning |
| DIY box-fan cleaner | One room or zone | Use a correctly sized filter, follow EPA construction and fan-safety directions, and keep the assembly stable and unobstructed | Performance, fit and safety depend on construction and the fan; it is not a whole-home system |
Using a MERV 13 furnace filter in HVAC systems
Check compatibility before installation
EPA recommends MERV 13 or higher for compatible HVAC systems during smoke periods. A higher-rated filter can increase resistance to airflow, so check the furnace, air-handler or heat-pump manual for the permitted filter rating and thickness. If the system struggles to move air, freezes a cooling coil, overheats, or produces unusual noise after installation, switch to the highest rating the manufacturer allows and arrange an HVAC inspection.
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- UNIVERSAL COMPATIBILITY: Fits most standard residential and commercial HVAC systems with a 1-inch filter. Including Carrier, Bryant, Payne & Honeywell. Actual size 5.75 x 24.75 x 0.75 Comparable to Filtrete MPR 1500-1900 and Honeywell FPR 10 filters.
- ADVANCED MERV 13 (MPR 1500 - 1900 / FPR 10) PERFORMANCE: High-efficiency filter media captures up to 98% of airborne particles including dust, pollen, pet dander, bacteria, smoke, and microscopic allergens for cleaner, healthier indoor air.
- ELECTROSTATICALLY CHARGED DESIGN: Premium synthetic pleated fibers attract and trap more particles without restricting airflow—helping maintain optimal HVAC system performance and energy efficiency.
- LONG-LASTING, DURABLE DESIGN: Heavy-duty beverage board frame with moisture-resistant backing and reinforced pleats provides up to 3 months of reliable filtration—outlasting traditional fiberglass filters.
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Install it so air cannot bypass it
- Turn the system off at the thermostat before opening the filter compartment.
- Read the airflow arrow on the filter and point it toward the blower or air handler.
- Seat the filter squarely so there are no visible gaps around its frame.
- Close and latch the compartment, then restore normal operation.
- Inspect the filter during the smoke event. Replace it when visibly dirty, loaded with ash, damaged or past its service interval; smoke may require replacement sooner than normal.
Continuous fan operation can improve removal if the system is designed for it and the indoor temperature remains safe. EPA cites a smoke-event estimate of about a 50% PM2.5 reduction for a high-efficiency HVAC filter running continuously. Even a typical low-efficiency filter running continuously may reduce particle concentrations by about 24%. These are guidance figures, not a guarantee for a particular home.
Run a portable air cleaner correctly
Place it where exposure is highest
Put the cleaner in the bedroom or other room occupied most, rather than in an empty hallway. Keep doors and windows closed. Leave clear space around the intake and outlet, and do not place the unit behind furniture, curtains or bedding. If the household spends the day in one room, move the cleaner there; clean air in an unused room does not protect people elsewhere.
Select capacity and operating speed
Use the manufacturer’s room-size or clean-air-delivery information as a starting point. A unit that is undersized for the room may still help, but it will need longer or faster operation. Run it as often as possible on the highest speed people can tolerate. Lower speeds are quieter but move less filtered air. Close the room when practical to keep the treated air from mixing with smoky air in the rest of the home.
Check ozone and maintenance
EPA advises using only California Air Resources Board (CARB)-certified air cleaners because they produce little or no ozone, a harmful air pollutant. Avoid devices marketed as ozone generators for smoke removal. Follow the cleaner’s filter-change indicator, inspect the filter during prolonged smoke, and keep replacement filters available before the next event.
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- MADE IN USA, SUSTAINABLY - Proudly manufactured by BNX Converting, LLC in Houston, TX, a registered and approved facility (EPA Registration # 101638-TX-1). Adopts single sided (one-piece) frame technology to reduce environmental waste and made sustainably from recycled cardboard. Classified in accordance with UL 900 (Certificate Number UL-US-2403701-0).
- SUPERIOR PERFORMANCE - The BNX MERV 13 air filter media outperforms standard fiberglass filters and adopts the latest in electrostatic filtration technology to capture maximum pollen, mold bacteria, smoke, carriers & other microscopic particles while maintaining industry leading superior low air flow resistance.
- CAPTURES MICROSCOPIC PARTICLES - The BNX air filter has a MERV 13 rating allowing it to capture 93% of microscopic airborne particles (3-10 um) without impacting air flow. Captures microscopic particles such as virus-carriers, bacteria, odors, smoke, and pollen, pet dander, allergens, dust, lint, mold, dust mites, smog. Noticeably cleaner air in 48 hours.
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Build a DIY box-fan air cleaner
A box fan paired with a furnace filter can provide a lower-cost cleaner for a single room when a commercial unit is unavailable. Use a newer fan in good condition and a filter that fits the intake side without gaps. EPA construction and fan-safety directions matter: secure the filter, keep the assembly upright and stable, leave the fan grille and exhaust unobstructed, and keep it away from water, children and pets. Do not leave a makeshift assembly where it can tip, overheat or block an exit. Replace the filter when it becomes loaded with smoke particles.
A DIY unit is not a substitute for an appropriately rated HVAC filter or a certified portable cleaner when those options are available. Its actual airflow depends on the fan, filter resistance, sealing and room size.
Create a cleaner-air room
Choose the room
- Select a room with few windows and doors.
- Do not use a room with a fireplace or other combustion appliance.
- Choose a room that can be closed off from the rest of the home and remains cool or warm enough for safe occupancy.
Set it up
- Close the room’s windows and door.
- Place a portable cleaner or safe DIY unit where air can circulate freely.
- Run the cleaner continuously or at the highest practical setting.
- Keep smoking, vaping, candles, incense, aerosols and cooking out of the room.
- Sleep, work or care for vulnerable household members there during the worst outdoor conditions.
A cleaner-air room reduces exposure; it does not make the rest of the building safe automatically. Keep the room closed and avoid opening it repeatedly.
Eliminate indoor sources that raise PM2.5
During a smoke episode, avoid activities that generate particles or gases:
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- ADVANCED MERV 13 (MPR 1500 - 1900 / FPR 10) PERFORMANCE: High-efficiency filter media captures up to 98% of airborne particles including dust, pollen, pet dander, bacteria, smoke, and microscopic allergens for cleaner, healthier indoor air.
- ELECTROSTATICALLY CHARGED DESIGN: Premium synthetic pleated fibers attract and trap more particles without restricting airflow—helping maintain optimal HVAC system performance and energy efficiency.
- LONG-LASTING, DURABLE DESIGN: Heavy-duty beverage board frame with moisture-resistant backing and reinforced pleats provides up to 3 months of reliable filtration—outlasting traditional fiberglass filters.
- PROUDLY MADE IN THE USA: Manufactured using high-quality materials in American facilities to ensure dependable performance, sustainable production, and cleaner indoor air you can trust.
- Smoking or vaping indoors.
- Wood fireplaces, gas fireplaces and candles.
- Gas or propane cooking unless essential; never use an oven or stove to heat the home.
- Frying, broiling, grilling or other high-heat cooking. If food must be prepared, choose lower-emission methods and use a properly vented range hood only if it exhausts safely and does not draw smoky outdoor air into the home.
- Spray cleaners, paints, solvents, fragrances and aerosol products.
- Vacuuming, which can resuspend settled particles unless using equipment designed to contain fine dust.
Keep doors between the home and an attached garage closed. Do not run engines, generators or other fuel-burning equipment indoors or in an attached garage, even with a door or window open.
Respirators for unavoidable outdoor exposure
If you must go outside while smoke is hazardous, CDC states that an N95 or P100 is most protective. Choose a NIOSH-approved model, inspect it before use and obtain a seal over the nose and mouth. Facial hair, an incorrect size or gaps around the edges reduce protection. Follow the manufacturer’s replacement guidance and leave the smoky area as soon as the task is complete.
A respirator is personal protective equipment. It does not filter the air in a house, car or workplace for other people, and it does not justify opening windows during a hazardous AQI.
Plan for power outages and equipment limits
Before smoke arrives
- Keep spare MERV 13-compatible HVAC filters and portable-cleaner filters sealed and stored.
- Check that a portable cleaner, fan and thermometer work before an alert.
- Identify a room that can serve as the cleaner-air room.
- Know where the HVAC recirculation and outdoor-air controls are located.
- Plan transportation to a library, community center or other cleaner-air shelter if cooling fails, without assuming any particular facility will be open.
During an outage
Filtration stops when electric equipment stops. Keep windows and doors closed as long as the indoor temperature remains safe, avoid all indoor combustion and monitor vulnerable people. Battery power stations or generators may run approved equipment only when used exactly as directed. A generator must remain outdoors, far from doors, windows and vents, because carbon monoxide can kill even when smoke levels seem manageable.
Know when to reopen the building
Wait for a current AQI or smoke advisory showing that outdoor air has improved. Then ventilate briefly when practical, rather than assuming one clear-looking hour is enough. Reopen windows or outdoor-air intakes only when conditions are better, and close them again if smoke returns. After the event, replace overloaded filters, wipe settled dust with damp methods, and resume normal ventilation and cooking practices gradually.
Quick Recap
Compare the main strategies
| Decision factor | Central HVAC filtration | Portable or DIY room cleaner | Cleaner-air room |
|---|---|---|---|
| Coverage | Can serve much of the home if the system circulates air effectively | Usually one room | One designated room, with people staying there |
| Particle removal | MERV 13 or higher when compatible; continuous high-efficiency operation is associated with an EPA estimate of about 50% PM2.5 reduction | Depends on filter efficiency, airflow and room size | Combines sealed-room control with filtration |
| Noise and energy | Higher fan use can add noise and electricity consumption | High speed is louder and uses more power | May concentrate people in one room but still needs cleaner power |
| Heat management | Cooling can continue in recirculation mode if the system has power | Most units add little heat but require electricity | Must remain thermally safe; relocate if it overheats |
| Ozone risk | Mechanical filtration does not require ozone; avoid ozone-generating add-ons | Prefer CARB-certified low-ozone cleaners | Depends on the cleaner used |
| Outage use | Stops without HVAC power | Stops without power unless safely backed up | Still reduces infiltration, but cannot remove accumulated particles without filtration |
A practical hazardous-AQI checklist
- Check the current AQI and smoke advisory for your location.
- Close windows, exterior doors and pet doors.
- Set HVAC and room air conditioners to recirculate; close permitted outdoor-air intakes.
- Install a correctly fitted MERV 13 filter if the HVAC manufacturer permits it.
- Run a portable HEPA cleaner or safely constructed box-fan cleaner in the occupied room.
- Stop smoking, vaping, combustion, aerosols, frying, broiling and vacuuming.
- Keep an N95 or P100 respirator available for necessary trips outside.
- Monitor indoor temperature and symptoms; move to another shelter if the home becomes unsafe.
- Keep replacement filters and backup power options ready.
- Reopen the home only after outdoor air improves.
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