Is smoke in your home? Here’s how to make an air purifier using a box fan
Wildfire Smoke Indoors? Build Your Own Air Purifier Today
Is smoke in your home Here - As wildfire smoke continues to blanket vast regions of the United States, residents are seeking ways to protect their indoor environments. Interest in air filtration solutions has surged dramatically, with many homeowners exploring how to construct their own air purifiers using readily available materials.
According to the federal AirNow monitoring system, a substantial portion of the country—stretching from Minnesota down to Virginia—experienced "very unhealthy" air conditions on Friday. This designation stems from elevated particulate matter concentrations resulting from major wildfire events.
Understanding Air Quality Alerts
The smoke plumes originate primarily from fires burning in Ontario, Canada, alongside significant blazes in northern Minnesota. Cities such as Duluth are currently facing hazardous air conditions at unprecedented levels, as documented by Minnesota Public Radio.
AirNow's interactive map displays a purple zone indicating "very unhealthy" air quality index readings ranging from 201 to 300. The Environmental Protection Agency explains that this threshold triggers public health warnings because "everyone may experience more serious health effects." Vulnerable populations include children, elderly individuals, and those suffering from cardiovascular or respiratory conditions.
Within these warning boundaries, numerous communities face even more severe "hazardous" conditions, representing an AQI of 301 or higher—a classification the EPA describes as "extremely rare."
The Science Behind the Smoke
Experts emphasize that fine inhalable particulate matter, commonly referred to as PM 2.5 (measuring 2.5 microns), poses significant health risks because it can penetrate deep into lung tissue.
Smaller ultrafine particles (PM 0.1) can pass into the bloodstream and organs, including the brain.
This observation comes from researchers at the University of Washington, highlighting how microscopic particles travel beyond the respiratory system.
Filter Ratings Matter
Whether upgrading your heating and cooling system or constructing a do-it-yourself cleaner, filters serve as the critical component. Their capacity to extract particulates and other airborne substances receives evaluation through Minimum Efficiency Reporting Values, abbreviated as MERV. Higher MERV numbers indicate greater ability to capture smaller contaminants such as smoke, bacteria, and viruses.
A MERV 13 rating signifies that a filter efficiently captures particles measuring between 0.3 and 1 micron. The California Air Resources Board, or CARB, lists examples including bacteria, droplet nuclei from sneezing, most tobacco smoke, and insecticide dust.
Upgrading to a filter rated MERV 13 or higher can be especially important during smoky periods to effectively remove fine particle pollution from smoke in the indoor air.
The EPA adds that most residential HVAC systems accommodate MERV 13 filters without issue, provided owners replace them regularly. When uncertain, consulting an HVAC technician ensures proper compatibility.
One consideration: HVAC systems only clean indoor air while actively running. For additional information on filter rating systems, listeners can visit member station LAist.
DIY Purifier Designs
Creating a functional air purifier requires minimal supplies: a box fan, quality air filters, and duct tape.
NPR previously shared instructions for constructing a Corsi-Rosenthal Box—a purifying cube utilizing four 20-inch MERV 13 filters, a matching 20-inch box fan, and two 20-inch cardboard panels.
A more budget-friendly alternative involves securing a single MERV filter to the rear of a box fan. This method, outlined by the Montana organization Climate Smart Missoula, recommends using newer fan models and ensuring the motor remains clean to prevent overheating.
The Centers for Disease Control and Prevention confirms that these homemade purifiers offer effective temporary relief, particularly when conventional options remain unavailable.
HEPA Filters and Certified Products
HEPA, standing for high-efficiency particulate air, represents the standard for many commercial air purifiers. According to CARB, HEPA performance approximates a MERV 17 rating.
A well-sealed HEPA filter is more than 99.9% efficient for all sizes of particles.
This statement originates from the American Society of Heating, Refrigerating, and Air-Conditioning Engineers, or ASHRAE.
When purchasing portable air cleaners, the EPA advises verifying the presence of a HEPA filter. Their online guide assists consumers in selecting units sized appropriately for their rooms. Additionally, California maintains a comprehensive table of state-certified air cleaners featuring over 1,000 products organized by brand, model number, and type.
Regardless of your chosen approach, experts recommend sealing doors, windows, and air ducts thoroughly to prevent smoke infiltration. Staying hydrated helps reduce irritation, and wearing a mask during outdoor activities provides additional protection, as NPR has previously reported.
This article was originally published on January 10, 2025, and has been updated to reflect current wildfire conditions affecting the United States.