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1Scan for outdated or missing drivers - takes under a minute2Clear out junk files and repair common Windows errors3Fix the driver behind crashes, sound loss and screen glitchesWhen outdoor AQI reaches hazardous levels, close windows and exterior doors, switch central heating or air conditioning to recirculate, and stop bringing outdoor air into the building if your equipment allows it. Run the best filtration your home can safely support, concentrate it in the room people use most, and eliminate indoor particle sources such as smoking, candles, fireplaces and high-heat cooking.
This guidance is aimed at hazardous particle pollution, particularly wildfire smoke. If the home becomes dangerously hot with windows closed, the U.S. Environmental Protection Agency (EPA) advises moving to another suitable shelter rather than overheating indoors.
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What to do first when the AQI is hazardous
- Close every window and exterior door. Check less obvious openings, including patio doors, basement windows and frequently used entry doors.
- Set central HVAC or room air conditioning to recirculate. If the system has an outdoor-air damper, fresh-air intake or ventilation setting, close it when the equipment permits. Do not disable equipment in a way that creates a safety problem; use the controls provided by the manufacturer.
- Run filtration continuously or as often as practical. Use a compatible MERV 13-or-higher HVAC filter, a portable air cleaner, or both. Keep the unit in the room that is occupied most.
- Stop activities that generate particles. Do not smoke or vape indoors, burn candles or incense, use a fireplace, operate gas or propane burners unnecessarily, spray aerosols, fry or broil food, or vacuum while trying to lower particle levels.
- Keep replacement filters available. Smoke can load a filter faster than normal household dust, so inspect it during the event rather than waiting for a routine change date.
Only reopen windows or outdoor-air intakes after outside conditions improve. A short improvement can be enough to ventilate, but check the current AQI before changing the setting and close the openings again if pollution rises.
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Why indoor smoke levels vary so much
A closed building is not automatically clean. Smoke enters through leaks, open doors, ventilation systems and gaps around windows. Building tightness, room size, outdoor concentration, filter fit and fan operation all change the result.
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- 20x20x1 MERV 13 air filter replacement for your air conditioner, furnace or HVAC system. Actual Size: 19 11/16’’ x 19 11/16’’ x 3/4‘’. Comparable with MPR 1500-1900 & FPR 10. Provides optimal defense with electrostatically charged filter media and industry leading low air flow resistance.
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- CAPTURES MICROSCOPIC PARTICLES - The BNX air filter has a MERV 13 rating allowing it to capture 98% of airborne particles 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.
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EPA guidance reports that, during wildfire-smoke events, indoor PM2.5 is generally about 55% to 60% of outdoor levels when windows and doors are closed and no portable air cleaner is running. Across homes, indoor-to-outdoor smoke levels can range from about 30% to 100%. These are smoke-event observations, not a guarantee for a particular house.
The same guidance reports that a high-efficiency HVAC filter operating continuously may lower PM2.5 by about 50%, while even a typical low-efficiency filter operating continuously may reduce concentrations by about 24%. The figures vary with the building, filter installation, fan runtime, room volume and outdoor concentration. A filter that does not seal properly, or a fan that rarely runs, will not deliver the same result.
Choose a filtration approach that fits your home
| Approach | Coverage | What it does well | Important limits | Power and safety considerations |
|---|---|---|---|---|
| Portable air cleaner | One room or a defined area | Lets you concentrate cleaning where people spend the most time; easy to move between rooms | Does not clean the entire home unless air can circulate between spaces; performance depends on room size, fan speed and filter condition | Requires electricity; use a low-ozone model and keep airflow unobstructed |
| DIY box-fan cleaner | One room | Can provide a lower-cost room-cleaning option when assembled correctly | Construction quality, filter fit and fan safety determine performance; it is not a substitute for a whole-home system | Follow EPA construction and fan-safety directions; keep the assembly stable and clear of curtains, furniture and walkways |
| HVAC filter rated MERV 13 or higher | Potentially the whole home served by the duct system | Uses existing ductwork and can reduce particles whenever the blower runs | Only works in connected spaces; some systems cannot handle the airflow resistance of a higher-rated filter | Confirm compatibility, install the filter in the correct direction and monitor the system for restricted airflow |
| Windows-open ventilation | Whole room or home | Useful only when outdoor air is cleaner than indoor air | During hazardous AQI it can bring smoke indoors and defeat filtration | Keep openings closed during the hazardous period; reopen only after conditions improve |
How to use a MERV 13 filter in central HVAC
Check compatibility before installing
EPA recommends MERV 13 or higher for compatible HVAC systems during smoke periods. Higher resistance can reduce airflow in systems that were not designed for it, so check the equipment manual, the filter slot and any guidance from the installer or manufacturer. If the system cannot safely use MERV 13, use the highest compatible rating rather than forcing a filter into the cabinet.
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Install it correctly
- Turn the HVAC system off if the manufacturer recommends doing so for filter changes.
- Remove the old filter and note its dimensions and the airflow arrow.
- Insert the replacement with the arrow pointing toward the blower or air handler.
- Make sure the filter sits flat and that air cannot bypass it around the frame.
- Restart the system and select recirculation. If available, use a fan setting that runs continuously during the smoke event, provided the system remains within its operating limits.
Inspect it during the smoke event
Look for visible loading, deformation or a filter that is pulled away from its frame. Replace a dirty filter promptly. Heavy smoke may require more frequent changes than the normal maintenance schedule. Keep at least one correctly sized spare so a replacement does not depend on store availability during an emergency.
Set up a portable air cleaner or a DIY cleaner
Portable air cleaner placement
- Choose the room where occupants spend the most time, such as a bedroom or living area.
- Close the room’s windows and door as much as practical.
- Place the cleaner where its intake and exhaust are not blocked by walls, curtains, furniture or bedding.
- Run it on the highest practical fan speed. A lower setting may be appropriate for sleep or noise, but it cleans less air per unit of time.
- Keep the unit running as often as possible during the hazardous period and follow its filter-change indicator or inspection instructions.
A portable unit is a room device, not a respirator and not a guarantee that every room in the home has the same air quality. If people move between rooms, move the cleaner when practical or use additional units for separate occupied spaces.
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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.
- 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.
DIY box-fan cleaner
A box fan fitted with an appropriate filter can be used as a room air cleaner when built according to EPA directions. The filter must be attached securely, the airflow direction must be correct and the assembly must remain stable. Keep it away from children, pets, water and anything that could pull material into the fan or block the intake. Do not place it where it can tip, overheat or obstruct an exit.
Inspect the filter and attachment points regularly. A loose filter leaves bypass gaps, while a damaged fan or unstable frame creates a safety hazard. If you cannot make a stable, unobstructed assembly, use a manufactured portable cleaner instead.
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A cleaner-air room gives household members a place to spend the worst part of the smoke event. The goal is not perfect air; it is the lowest particle concentration you can maintain with the building and equipment available.
- Pick the room. Choose a space with few windows and doors and no fireplace. A bedroom is often practical because it can remain closed for long periods.
- Seal the operating pattern. Keep windows and the door closed except for necessary entry and exit. Avoid propping the door open.
- Run filtration. Place a portable cleaner in the room, or use a correctly assembled box-fan cleaner. If the central system serves the room, use the compatible HVAC filter and recirculation setting as well.
- Remove particle sources. Do not smoke, vape, burn candles, use a fireplace, spray products or cook in the room. Avoid bringing in smoky clothing or equipment when possible.
- Limit traffic. Each door opening exchanges indoor and outdoor air. Organize supplies, water, medicines and chargers in advance so the room can stay closed.
- Monitor comfort. A closed room can become warm or stuffy. If heat becomes unsafe, move to another suitable shelter rather than keeping people in dangerous temperatures.
Stop indoor activities that raise particle levels
Filtration can be overwhelmed by a strong source close to occupants. During hazardous outdoor conditions, avoid:
- Smoking cigarettes, cigars or other products, and vaping.
- Burning candles, incense or wood in a fireplace or stove.
- Using gas or propane stoves or appliances when an alternative is available.
- Frying, broiling or cooking at high heat. If food must be prepared, choose lower-emission methods and use the range hood only if it vents safely for the current conditions; a hood that exhausts outdoors can draw smoky air through leaks in a tight home.
- Spraying aerosols, fragrances, cleaners, pesticides or other products.
- Vacuuming, which can disturb settled particles unless the equipment is specifically designed to contain fine dust.
These restrictions apply even when the activity is indoors. Smoke and combustion products generated inside begin at breathing height and can raise concentrations faster than a distant air cleaner can remove them.
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- 20x20x1 MERV 13 air filter replacement for your air conditioner, furnace or HVAC system. Actual Size: 19 11/16’’ x 19 11/16’’ x 3/4‘’. Comparable with MPR 1500-1900 & FPR 10. Provides optimal defense with electrostatically charged filter media and superior low air flow resistance. Based on ASHRAE Standard 52.2-2017 Initial Efficiency / Resistance.
- 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.
- BNX Quality Promise & Applications - BNX is committed to delivering the highest quality American made safety products, made with American workers, and using the latest automated manufacturing processes and technology with the strictest quality standards.
Manage heat when windows must stay closed
Closing windows protects against outdoor smoke but can make a home warmer, especially during a heat wave or a power interruption. Use air conditioning in recirculation mode if available. Shade sun-facing windows from the inside, reduce unnecessary heat-producing activity and stay in the coolest room that can be kept clean.
Do not trade smoke exposure for dangerous heat exposure. EPA advises seeking another shelter if the home cannot remain safely cool with windows and doors closed. Choose a location that can provide cleaner air and safe temperatures, and follow local emergency instructions.
What changes during a power outage
Central HVAC systems and most portable cleaners need electricity, so their filtration benefit stops when the power is off. Close windows and doors, avoid all indoor combustion and particle-generating activities, and keep people in the cleanest available room until power or a safer shelter is available. Do not operate fuel-burning equipment indoors or in an enclosed area. A battery-powered device can help only if it is designed for that use and does not create a fire or ventilation hazard.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.If you must go outside
Staying indoors is generally the primary way to reduce smoke exposure when outdoor AQI is hazardous. If leaving is unavoidable, the CDC states that “An N95 or P100 is most protective.” Use a properly fitted, NIOSH-approved respirator and follow the product’s instructions. Facial hair, gaps around the nose and cheeks, an incorrect size or poor strap placement can reduce protection.
A respirator protects the person wearing it while outside; it does not clean the home. Remove smoky outer layers when returning, keep doors closed, and resume the home’s recirculation and filtration settings.
Rank #4
- UNIVERSAL COMPATIBILITY: Fits most standard residential and commercial HVAC systems with a standard 1-inch filter slot. Including Carrier, Bryant, Payne & Honeywell. Actual size 19.75 x 19.75 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.
- 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.
Prepare before the next smoke event
- Measure the HVAC filter slot and keep compatible MERV 13 filters or the highest compatible rating on hand.
- Check portable cleaner filters, power cords, controls and placement space.
- If using a DIY box-fan cleaner, assemble and test it before smoke arrives; verify that it is stable and unobstructed.
- Identify the cleaner-air room and store water, medicines, chargers and other essentials there.
- Write down how to select recirculation and how to close the outdoor-air damper or fresh-air intake, if your system has one.
- Keep a supply of properly fitted N95 or P100 respirators for unavoidable outdoor trips.
- Know where household members can go if the home becomes too hot or loses power.
Troubleshooting common problems
The AQI is hazardous but indoor air still smells smoky
Check that every window and exterior door is closed, the HVAC system is recirculating, and the filter is installed in the correct direction with no bypass gap. Inspect portable cleaner placement and increase fan speed if practical. Look for indoor sources such as cooking, candles, smoking or a fireplace.
The HVAC system sounds strained after installing a higher-rated filter
Turn to the equipment manual or a qualified HVAC professional for compatibility guidance. A system that cannot maintain safe airflow should not be forced to use a filter rating beyond its design. Use the highest compatible filter and supplement the occupied room with a portable cleaner.
One room is clean but the rest of the home is not
Portable and DIY cleaners target a room. Keep the cleaner-air room closed and move a unit to the room people occupy next, or use additional units if available. Central HVAC filtration can help connected rooms only while the blower circulates air through them.
The filter becomes dirty quickly
Frequent loading is expected during heavy smoke. Replace the filter when dirty, keep spares available and inspect the filter more often than during ordinary conditions. A dirty filter can restrict airflow and reduce the system’s usefulness.
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Cooking can overwhelm filtration, especially frying or broiling. Postpone high-heat cooking, choose a lower-emission method and keep the activity away from the cleaner-air room. Never use a fireplace or fuel-burning appliance as a way to heat or cook indoors during a smoke event.
How to judge whether a solution is appropriate
Use these questions before relying on any device or setup:
- Does it cover the room people will actually occupy, or only a distant space?
- Can the existing HVAC system safely handle the filter rating?
- Will the filter seal tightly, and are replacements available in the correct size?
- Can the device run at a tolerable noise and energy level for the hours it must operate?
- Does the cleaner have a low-ozone certification? EPA advises using only California Air Resources Board (CARB)-certified air cleaners because they produce little or no ozone, a harmful air pollutant.
- What happens if the power fails or the room becomes too hot?
No single device compensates for an open window, an indoor combustion source or an unsafe temperature. The strongest practical setup combines closed openings, recirculated HVAC where compatible, room-focused filtration, source control and a plan for heat or power problems.
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