Research on DIY Air Cleaners to Reduce Wildfire Smoke Indoors
On this page:
- Study Overview
- UL Safety Report Findings
- Frequently Asked Questions
- DIY Air Cleaner to Reduce Wildfire Smoke Indoors Infographic
- Related Resources, Presentations, and References
Everyone deserves access to clean indoor air during wildfire smoke events. But commercial air cleaners can be difficult to obtain when there are smoky conditions from wildfires because of limited availability or high cost. Many health and air quality agencies and nonprofits are providing instructions and parts for making Do-It-Yourself (DIY) air cleaners as a solution to reducing smoke indoors. DIY air cleaners are made by attaching an air filter to a box fan with tape, brackets or a bungee cord. With their use, concerns have been raised about the potential for the box fans to overheat when operated with a filter attached, which could pose a fire or burn risk.
At this time, there is minimal information on how effective DIY air cleaners are at removing smoke particles. Limited data published in the scientific literature, preliminary testing results from EPA and several anecdotal reports from state, local, and tribal agencies suggest these DIY air cleaners may help reduce exposure to the particles in smoke.
EPA is conducting research to evaluate DIY air cleaners to answer questions from EPA partners and the public about their effectiveness and safety. The research is part of a multi-faceted study called the Wildfire Advancing Science Partnerships for Indoor Reductions of Smoke Exposures (ASPIRE) Study. The objectives of the Wildfire - ASPIRE Study are to compare indoor and outdoor fine particulate matter (PM2.5) concentrations, a main component of wildfire smoke, and to develop strategies for reducing indoor pollutant concentrations in public buildings during wildland fire smoke events.
EPA is testing the effectiveness of DIY air cleaners and commercial air cleaners in removing smoke. The research is being conducted in laboratories in Research Triangle Park, North Carolina. Simulated wildfire smoke made from smoldering pine needles is being used in a sealed room-sized chamber to determine the Clean Air Delivery Rate (CADR) of the cleaners. The CADR is a standard measure of how well a commercial air cleaner can remove particles from a room of a given size. The results will be posted on this web page when the evaluation is complete, peer reviewed and published. Preliminary findings from a limited set of test runs in the lab are available in a scientific presentation in EPA’s Science Inventory by using the link below. The testing suggests a Clean Air Delivery Rate that is similar to a small size commercial air cleaner.
With DIY Air Cleaners becoming more popular, concerns have been raised that operating a box fan with an air filter attached – particularly a dirty air filter – might cause the fan components to overheat, posing a fire or burn risk. EPA researchers collaborated with Chemical Insights Institute of Underwriters Laboratories Inc. (UL) to assess the fire and burn risks from DIY air cleaners.
As a first step to assess the safety of DIY air cleaners, UL tested five models of box fans with clean filters, as well as with filters loaded with smoke and dust provided by EPA. The DIY air cleaners were tested under several possible scenarios, including a simulation of an extreme scenario where the front and back of the fan were both blocked for an extended period of seven hours. UL has published the results of this testing in the report, Wildfire Safety Research: An Evaluation of DIY Air Filtration. Preliminary results show that throughout the testing, temperatures of all fan components remained safely below recognized temperature safety standards. None of the scenarios tested posed any observable fire hazards.
EPA cannot assure the results of the safety testing are representative of all DIY air cleaners in all scenarios because there is a wide range of variability in the materials used and how the cleaners can be built or operated. In addition, there are inherent risks associated with operating any electrical device. For more important safety information and tips, read the Frequently Asked Questions for DIY Air Cleaners on this page and visit EPA’s web page on Air Cleaners and Air Filters in the Home at: https://www.epa.gov/indoor-air-quality-iaq/air-cleaners-and-air-filters-home.
- UL Report: Wildfire Safety Research: An Evaluation of DIY Air Filtration
- Air Cleaners and Air Filters in the Home
The following excerpt is from the Wildfire Safety Research: Evaluation of DIY Air Filtration Report, published by Chemical Insights Institute of Underwriters Laboratories Inc. (UL).
“Across all fan/filter test scenarios, the most notable temperature increases were observed at the motor and motor windings. However, all measured temperatures fell below the maximum acceptable thresholds defined by the market safety standard for electric fans (UL 507). Exterior surfaces that can come into direct contact with people remained below 36 °C, which is below the first-degree burn potential of 47.5 °C. Further, an extreme scenario where both the front and back of the fan were blocked for an extended period of 7 hours did not pose any observable fire hazards. And after an initial rise, temperature remained steady throughout the test.”
- None of the filter/fan test scenarios caught fire.
- Different brands of fans showed similar temperature patterns across the filter scenarios.
- Temperatures on the external fan components remained near room air temperature when filters were attached.
- Temperatures on the external fan components were elevated above ambient temperature, but below hazard thresholds for the extreme scenario with both fan sides blocked.
- Attaching a filter and operating the fan resulted in an increase in internal fan component temperatures regardless of filter type (i.e., clean, smoke-loaded, and dust-loaded filters). However, all measured temperatures fell below maximum acceptable safety thresholds.
- For the extreme conditions, when both sides of the fan were blocked, measured temperatures increased over the course of the first 20 minutes and then temperatures remained steady for an extended seven-hour run period.
- The highest temperature increase, nearly 60 °C, was observed on the internal fan components with a dust laden filter.
- Air flow reductions were observed when filters were placed on the fans.
- Filter conditions did not influence electric current, resistance, or power applied to the fan.
Why did the EPA team up with UL to safety-test air cleaners?
As part of the Biden-Harris Administration’s commitment to address the growing threat of wildfires, the EPA is conducting research to provide actionable information to help Americans stay safe during a wildfire.
Everyone deserves access to clean air, but cost, availability, and access to a reliable power source (especially during fire events) can be barriers for people impacted by wildfires. Many health and air quality agencies and nonprofits have begun providing instructions and parts for making Do-It-Yourself (DIY) air cleaners. DIY air cleaners are made from a box fan with a high efficiency home air filter attached with tape, brackets or a bungee cord. However, concerns have been raised about the potential for the box fan motor to overheat when operated with a filter attached, posing a potential fire or burn risk. EPA researchers wanted to know if these DIY air cleaners are likely to pose a safety risk for people using them.
How did EPA and UL evaluate safety?
EPA partnered with Chemical Insights Institute of Underwriters Laboratories Inc. (UL), a nonprofit research organization, to assess the potential fire and burn risks of operating DIY air cleaners. UL evaluated the risks of fan overheating and potential fire ignition resulting from different fans and filters. EPA researchers provided sample air filters to UL that had been prepared in the laboratory. Some filters contained air pollutants from simulated wildfire smoke and others contained heavy household dust. UL attached the filters to several models of box fans. They then ran a series of tests under different conditions, and measured the temperature on different components of the fan.
This type of testing helps to assess whether the fans reach temperatures that pose a fire or burn hazard. However, the study was limited to several box fan models and may not be representative of all fans or potential filter configurations.
Are DIY air cleaners safe?
All measured temperatures for the scenarios tested met temperature standards for electric fans (UL 507). This includes an extreme scenario where both the front and back of the fan were blocked for an extended period of seven hours. This and all other evaluated scenarios did not pose any observable fire hazards during testing.
However, there is a wide range of variability in the types of fans and filters used, and how these DIY air cleaners can be built or operated. Therefore, EPA cannot assure these results are representative of all scenarios. In addition, there are inherent risks associated with operating any electrical device. Because of this, EPA recommends that anyone who uses a DIY air cleaner follow important safety tips.
What safety tips should I follow?
- If you build a DIY air cleaner, use a newer model box fan (2012 or later). The newer models have added safety features. Fans built prior to 2012 were not tested, and pose known fire risks.
- Use fans that have been verified by an accredited third party to meet the UL 507 safety standard for electric fans or equivalent. To find a verified fan, look for one with a UL or ETL safety marking.
- EPA does not recommend using DIY air cleaners built with older model box fans (before 2012), but if they are used, they should not be used unattended or while sleeping.
- Anyone who uses a DIY air cleaner should follow the box fan manufacturer’s instructions, which can include: Don't leave children unattended when the fan is in use; don't use an extension cord, and don't use a damaged or malfunctioning fan.
- Always ensure that there are working smoke detectors throughout the home.
- During smoke events, filters will need to be replaced more often, as well as at the end of a smoke event. Not changing the filter regularly may reduce how well the filter works and may release smoke particles into the air. Make sure to keep extra filters on hand and change the filter when it starts to look dirty or release smoke odors.
Are DIY air cleaners effective?
Currently only limited testing has been conducted on how effective these DIY air cleaners are at removing smoke particles. Some published literature, preliminary EPA testing, and anecdotal reports suggest they may be effective in removing particles from smoke, with a Clean Air Delivery Rate that may be similar to that of smaller commercial air cleaners. EPA researchers are testing the effectiveness of DIY air cleaners in the laboratory to determine how well these DIY air cleaners work to remove smoke particles indoors compared to commercial air cleaners and how much it costs to operate them (electricity and filter replacement costs).
How do I build an air cleaner/Which design should I use?
There are a number of designs and instructions available on the internet. Missoula Public Health, a partner in the Wildfire - ASPIRE Study, has a web page that describes how to make and use a DIY air cleaner.
How many air cleaners do I need?
You may benefit from having more than one air cleaner if smoke is very thick or your home is not well sealed from the outdoor environment. However, if you can designate one room in your home as a cleaner air room that people spend time in when it is smoky out, then one air cleaner may be sufficient. Some people have found it to be effective to move one air cleaner from room to room. Learn more about air filtration and how to create a cleaner air room at: https://www.epa.gov/indoor-air-quality-iaq/air-cleaners-and-air-filters-home.
What else should I know about using a DIY air cleaner?
There may be drawbacks to using a DIY air cleaner as compared to a commercial air cleaner, such as increased noise and heat generation from the fan motor, and limited data on how well DIY air cleaners filter smoke particles. When commercial air cleaners are not available or affordable, DIY air cleaners may offer some protection from smoke indoors. It is also important to take other steps to reduce your exposure to particles during wildfires, and to keep an eye on temperature and make sure you have a way to stay cool, even if that means going somewhere else.
- AirNow.gov’s Fire and Health web page
- Air Cleaners and Air Filters in the Home
- Create a Clean Room to Protect Indoor Air Quality During a Wildfire
- Wildfires and Indoor Air Quality
- Montana Wildfire Smoke: DIY Fan/Filter Combos
- Emerging Approaches to Cleaner Indoor Air During Wildfires Presented to the California Air Pollution Control Officers Association 4/21/2021
- Xiang, Huang, Shirai, Liu, Carmona, Zuidema, Austin, Gould, Larson, Seto. (2021). Field measurements of PM2.5 infiltration factor and portable air cleaner effectiveness during wildfire episodes in US residences. Science of the Total Environment 773 p 145642
- May, Dixon, Jaffe. (2021). Impact of wildfire smoke events on indoor air quality and evaluation of a low-cost filtration method. Aerosol and Air Quality Research 21, 210046
- Portable Air Cleaner Test Report – Box Fan Filter March 2021. Accessed August 17, 2021.
- Puget Sound Clean Air Agency. DIY Air Filter webpage. Accessed August 17, 2021.