Introduction: Box Fan Allergy Filter

With Allergy season nearly upon us I thought this would be a helpful Ibble to create. The concept is simple, and under $50 CDN to build. We are simply attaching a 20"x20" 3M micro allergen filter to a standard 20" by 20" Sunbeam box fan. There are many advanced versions of this design to be found on the internet but I have used the KISS method of construction. I have not implemented any special channels or anything very high tech.

Step 1: Things I Bought

The 3M filter was purchased at my local Home Depot. It is a Micro Allergen Filter that does a great job on Dust and Lint, and on Pollen and other junk. It cost $17.99.

The Sunbeam box fan was purchased on e-bay. I bought it from a supplier in Toronto because he advertised free shipping but these things can be found anywhere. I could have bought it at Walmart for the same price, but they don't deliver :) It was roughly $30.

Step 2: Construction 1

The filter is held in place by a piece of scrap hardwood flooring I had on hand. It is roughly 20 inches long to brace the top of the filter against the back frame of the fan. This is the back of the fan, or the intake, so make sure the airflow direction on your filter is in the correct direction.

I simply removed the upper two screws that hold the fan shroud on, and replaced them with longer screws to accommodate the thickness of the filter and the piece of wooden flooring.

I marked the hole locations with a black marker and drilled holes through the wooden flooring so a screw could pass through, and line up with the holes in the frame of the fan.

Special Note: Holes had to be marked and cut into the furnace filter at this point. Do not try to drill the holes through the top of the filter. The drill bit will catch on the filter cloth and wind it completely around your drill bit...been there done that. I ended up using an awl to make the holes through the filter.

The last photo here shows the marked wood and filter screwed to the top of the frame of the fan. These are the only two screws that attach the filter to the frame of the fan.

Step 3: Construction 2

The standard Sunbeam 20" box fan comes with 2 plastic feet that snap onto the bottom of the frame. Conveniently, they have a lip that can catch the bottom edge of the filter perfectly.

I used another 20" piece of hard wood flooring to wedge between the filter and the lip on the feet of the fan so the bottom of the filter is kept secure simply by friction. The bottom piece of wood does not need to be screwed to the Fan frame.

The last thing to watch out for in the assembly, is the power cord. It attaches to the center of the fan on the back of the frame. Simply cut a small hole through the filter cloth (not with your drill) to allow for the power cord to be plugged into the back of the fan. It is a bit of a trial to line the hole up properly. I used my awl to ease a hole through the filter cloth.

Step 4: The Finished Product

So there you have it. Two screws, a couple pieces of scrap wood, a box fan and a Furnace filter, and all your allergy problems are least when you are indoors. You might notice that the edge of the filter is sealed quite well against the frame of the fan even at the corners. I suspect making this would cost less than the allergy medication that you may have to buy at the pharmacy this spring and summer. I have 2 cats and 2 dogs so a filter like this not only helps with the pollen and dust allergies, it helps control pet hair that seems to make its way everywhere in my house. Cheers!