DIY – Box Fan MERV 13 versus HEPA Air Purifier

Here in San Francisco and surrounding areas kids are stuck indoors during this smoke wave caused by our wild fires with little or no air filtration. In San Francisco the school buildings are older and are not setup to have building wide air filtration.

Since the last fires, I have been curious about the DIY box fan air purifier made from items that can be found in most hardware stores- box fan, 20-inch x 20-inch x 1-inch MERV 13 filter and some duct tape.

There is a serious need for air filtration in schools and homes. How well will this DIY set-up clean the air?

Some parents of children with breathing issues are deciding to keep their kids home.
The SFUSD current response to the unhealthy air quality is to close windows and stay indoors, no current plans for air filtration due to cost.

Following the instructions from the Mariposa County Health Department, “How to Build an Inexpensive Room Filter”, we made our Box Fan room filter. In 2 separate rooms

Using our Lighthouse 3016-IAQ Laser particle counter, air samples were collected for 2 minutes, with a 2 min delay. This set-up was done in 2 rooms: one with the box fan and one with the HEPA filter.
Box Fan was able to drop PM2.5 particulates down 77%, the HEPA filter dropped the PM10 down 94.46%

See results complete results in chart below:

After testing, I was impressed how well the DIY Box Fan was able to remove particulates from the air. Yes, HEPA will provide more filtration, but if cost is an issue than the DIY Box Fan MERV 13 is a sensible choice. Further testing needs to be done with higher MERV ratings and over longer periods of time.