Uploaded January 2026 | Updated September 2026, 2 hours ago
I saw this idea first on This Old House a few years ago. They just taped four filters together, taped a board to one open end, and taped a box fan to the other open end. I have been using this in my shed, using four MERV 14 2-inch filters, for a while and occasionally taking them outside to knock off/blow out the sawdust. Now that I have added insulation to the ceiling of my shed, this fan contraption no longer fits, and I decided to finally build something more permanent so I could mount it to a wall.
How to Make a DIY Air Filter | Ask This Old House
youtu.be/aw7fUMhNov8?si=_iujJrYQPxp3VLja
The first one I built (I have three now) was a bit too snug and I ended up using smaller. 1-inch, filters than I planned and am using it in the house.
The second fits 20x20x2 filters that actually measure at 19.5-in x 19.5-in x 1.75-in. Slightly larger filters may fit or prefilters may be able to be added (need to get some).
The third is designed for Filtrete 20x20x1 filters (19.6-in x 19.6-in x 0.78-in) for use at my laser. It also allows a bit more space to add prefilters in eventually.
I constructed the four sides edge-joining with pocket holes and double-sided tape and then edge-to-face joining the four sides together. I attached this proto-box to the backplane using wood screws through the back. I joined the frontplane pieces together, pocket hole screws and tape again.
I disassembled the fan so that I could pull the power cord through and mount it to the frontplane. The model I used has a single screw at the base to remove and three internal latches at the top. Once these are free latches are free the face of the fan slides down. I cut out a few screen pieces on the back to pull the power cord through to keep it from making a gap between the fan and the frontplane. I also cut a small slot between a corner junction to slide the power cord through so it is back outside the fan frame.
Laying the fan out on the frontplane, facing out and centering it by eye, though it could be measured out if desired, I selected six spots to drill pilot holes through the fan housing and into the frontplane. I then attached the fan housing to the frontplane using short wood screws. I added four offcuts to four corners to help with aligning the frontplane to the box and added the latches to the corners perpendicular to the offcuts.
I used some weather stripping on the inside of the frontplane and backplane to help seal the filters and provide some compression. The filters are taped together edge to face - I found cloth/paper packing tape the easiest to use, tacking the pieces together first – ensuring the filters are positioned to flow into the box. This unit of filters just slides into the box, prefilters can be slide on the outside edges of the filters if desired. The frontplane just latches onto the box on top of this.
I added a French-cleat and block to the back so I could mount it to the wall.
Utilitech 20-in High Velocity Indoor Box Fan – from Lowe’s – Item #809484 | Model #FB50-16HB (or 16H)
Reliabilt 3.313-mm Touch Latch Cabinet Latch – from Lowe’s - Item #311968 | Model #S890-210 (I would recommend finding a different model that allows better alignment though)
20x20x1 MERV 13 (1900 MPR) Filters – from Lowe’s - Item #136039 |Model #MA02DC-6
20x20x2 MERV 13 Filterbuy Filters – from Amazon – UPC 717267063586
Cut Sheet (1/2-in plywood) for the 2-in filters (19.5-in x 19.5-in x 1.75-in, may be able to support slightly larger):
• (1) Backplane – 22.50-in x 22.50-in
• (4) Frontplane – 20.25-in x 2.25-in
• (4) Side Top – 17.75-in x 2.75-in
• (4) Side Bottom – 17.75-in x 1.50-in
• (8) Side Front & Back – 22.00-in x 1.00-in
Cut Sheet (1/2-in plywood) for the 1-in filters (19.6-in x 19.6-in x 0.78-in, should be able to handle most 20x20x1 filters):
• (1) Backplane – 22.00-in x 22.00-in
• (4) Frontplane – 20.00-in x 2.00-in
• (4) Side Top – 18.00-in x 2.00-in
• (4) Side Bottom – 18.00-in x 1.50-in
• (8) Side Front & Back – 21.50-in x 1.00-in
I saw this idea first on This Old House a few years ago. They just taped four filters together, taped a board to one open end, and taped a box fan to the other open end. I have been using this in my shed, using four MERV 14 2-inch filters, for a while and occasionally taking them outside to knock off/blow out the sawdust. Now that I have added insulation to the ceiling of my shed, this fan contraption no longer fits, and I decided to finally build something more permanent so I could mount it to a wall.
How to Make a DIY Air Filter | Ask This Old House
youtu.be/aw7fUMhNov8?si=_iujJrYQPxp3VLja
The first one I built (I have three now) was a bit too snug and I ended up using smaller. 1-inch, filters than I planned and am using it in the house.
The second fits 20x20x2 filters that actually measure at 19.5-in x 19.5-in x 1.75-in. Slightly larger filters may fit or prefilters may be able to be added (need to get some).
The third is designed for Filtrete 20x20x1 filters (19.6-in x 19.6-in x 0.78-in) for use at my laser. It also allows a bit more space to add prefilters in eventually.
I constructed the four sides edge-joining with pocket holes and double-sided tape and then edge-to-face joining the four sides together. I attached this proto-box to the backplane using wood screws through the back. I joined the frontplane pieces together, pocket hole screws and tape again.
I disassembled the fan so that I could pull the power cord through and mount it to the frontplane. The model I used has a single screw at the base to remove and three internal latches at the top. Once these are free latches are free the face of the fan slides down. I cut out a few screen pieces on the back to pull the power cord through to keep it from making a gap between the fan and the frontplane. I also cut a small slot between a corner junction to slide the power cord through so it is back outside the fan frame.
Laying the fan out on the frontplane, facing out and centering it by eye, though it could be measured out if desired, I selected six spots to drill pilot holes through the fan housing and into the frontplane. I then attached the fan housing to the frontplane using short wood screws. I added four offcuts to four corners to help with aligning the frontplane to the box and added the latches to the corners perpendicular to the offcuts.
I used some weather stripping on the inside of the frontplane and backplane to help seal the filters and provide some compression. The filters are taped together edge to face - I found cloth/paper packing tape the easiest to use, tacking the pieces together first – ensuring the filters are positioned to flow into the box. This unit of filters just slides into the box, prefilters can be slide on the outside edges of the filters if desired. The frontplane just latches onto the box on top of this.
I added a French-cleat and block to the back so I could mount it to the wall.
Utilitech 20-in High Velocity Indoor Box Fan – from Lowe’s – Item #809484 | Model #FB50-16HB (or 16H)
Reliabilt 3.313-mm Touch Latch Cabinet Latch – from Lowe’s - Item #311968 | Model #S890-210 (I would recommend finding a different model that allows better alignment though)
20x20x1 MERV 13 (1900 MPR) Filters – from Lowe’s - Item #136039 |Model #MA02DC-6
20x20x2 MERV 13 Filterbuy Filters – from Amazon – UPC 717267063586
Cut Sheet (1/2-in plywood) for the 2-in filters (19.5-in x 19.5-in x 1.75-in, may be able to support slightly larger):
• (1) Backplane – 22.50-in x 22.50-in
• (4) Frontplane – 20.25-in x 2.25-in
• (4) Side Top – 17.75-in x 2.75-in
• (4) Side Bottom – 17.75-in x 1.50-in
• (8) Side Front & Back – 22.00-in x 1.00-in
Cut Sheet (1/2-in plywood) for the 1-in filters (19.6-in x 19.6-in x 0.78-in, should be able to handle most 20x20x1 filters):
• (1) Backplane – 22.00-in x 22.00-in
• (4) Frontplane – 20.00-in x 2.00-in
• (4) Side Top – 18.00-in x 2.00-in
• (4) Side Bottom – 18.00-in x 1.50-in
• (8) Side Front & Back – 21.50-in x 1.00-in
