Wildfire smoke is becoming a recurring indoor air problem, not just an outdoor hazard, and the Environmental Protection Agency says a low-cost do-it-yourself air cleaner can help reduce smoke particles inside homes.
EPA research says DIY air cleaners made with a newer box fan and a MERV 13 air filter can be a “cost-effective method” for reducing indoor smoke concentrations. The agency recommends using newer, certified box fans with added safety features, preferably 2012 models or newer, and says performance can improve with a cardboard shroud, thicker filters or multiple-filter designs.
The guidance comes as more households face wildfire smoke events that can send fine particles into homes through windows, doors, cracks and ventilation systems. Those particles, often discussed as PM2.5, are small enough to travel deep into the lungs and can worsen asthma, irritate airways and increase risk for people with heart or lung disease.
EPA’s basic message is that filtration matters. A DIY air cleaner does not replace broader smoke-prevention steps, but it can be part of a cleaner-air room strategy when outdoor air quality is poor. The agency’s DIY air cleaner research pagesays the basic design can be improved by adding a cardboard shroud, using thicker filters or using multiple filters.
The simplest design uses a box fan attached to a high-efficiency filter. As the fan pulls air through the filter, particles are captured before cleaner air circulates back into the room. A cardboard shroud around the fan can reduce air leaking around the edges and improve cleaning efficiency.
Research published in Indoor Air found that DIY air cleaners can reduce smoke concentrations indoors and may provide clean air delivery rates comparable to lower-cost commercial air cleaners sized for smaller rooms. The study concluded that DIY air cleaners can be a viable approach to improving indoor air quality during smoke events.
The approach is not without caveats. A DIY unit should be placed where airflow is not blocked, should not be used with an old or damaged fan and should not be left running unattended if safety is uncertain. Filters also need to be replaced when they become dirty, especially during heavy smoke events.
Commercial portable air cleaners remain a strong option for many households, particularly when matched to room size and used with a true HEPA filter. But the DIY model gives families a more accessible alternative when supply, cost or urgency is a barrier.
The broader lesson is that respiratory protection increasingly starts at home. Outdoor air quality events are not just outdoor problems. Smoke can enter through cracks, ventilation systems, doors and windows, raising indoor particle levels even when the home appears sealed.
For readers building a basic respiratory-health toolkit, EPA’s guidance points toward a few practical priorities: track local air quality, reduce smoke entry, use filtration in the rooms where people spend the most time, and pay special attention to anyone with asthma, COPD or other breathing vulnerabilities.
Wildfire smoke may be unpredictable. Indoor air preparation does not have to be.
Sources: EPA DIY air cleaner research; EPA DIY air cleaner infographic; Indoor Air study on DIY air cleaner design
