Furnace Filter Case Fan Air Purifier

These air purifier boxes are loosely based on the original Corsi-Rosenthal design and the DIY hardboard kits from cleanairkits.com. This in-depth video from Healthy Home Guide explains how these types of filters improve on the noise, aesthetics, power requirements, and size of the original design, while still providing excellent air cleaning, superior to many commercially available products using proprietary filters and costing much more. 

These would make excellent gifts and be particularly useful in households with allergy sufferers or to reduce fine particulates secondary to wildfire smoke, 3D printing, etc. Two versions are available: 1) Uses 2 - 16x25x1 inch (actual: 15 5/8 x 24 5/8 x 25/32 in.; 396x625x19mm) MERV 13 or 14 filters 2) Uses 2 - 20x25x1 inch (actual: 19 5/8 x 24 5/8 x 25/32 in.; 498x625x19mm) MERV 13 or 14 filters. The 16x25x1 version can be printed on a 220x220mm bed. Both use six inexpensive 120mm high static pressure case fans and require approximately 2kg+ of filament. Each can be produced for less than $100 with careful sourcing of materials.

Products I used (approximate cost paid)

• Filters (2): Filtrete®2500 (MERV 14) Filters: (~$10/ea; packs of 4 on sale at Costco). $20
• 120mm 12v fans (6): Arctic Air P12. Packs of 5. (~$2.50-$5/each).   $15-$30
• Filament: PLA is fine (I used Aceaddity Flash PLA+ on sale for ~$9kg); ~2kg:  (~$9-15/kg): $20-$30
• 12v 2amp power supply: $6-10
• Fan controller 12v 2amp: $5
• 6-Fan Wire Harness: $6
• Misc. wire, wire connectors (or solder), 35 or 40mm M3 screws-washers-nuts, and weatherstripping: ~$5

Total: ~$80-$99

• Optional Filter Covers: Attach ¾ - 1 in. adhesive Velcro hook side tape to the front and back frame and then attach:
  • Activated Carbon Pre-filter. Fits best on a 16x25: $12-$18 -or-
  • Breathable Fabric that will adhere to velcro hooks -or-
  • Cheap polyester indoor/outdoor carpet (without any backing) (photo above) $5

Total: ~$95-$125

Print List:

• (5) - Stiffeners
• (4) - Panel Connectors
• (2) - Bases (one with, for power supply connector and one without a hole)
• (2) - Center Panels
• (2) - Top Panels. Print one with a hole and one with no hole if using fan controller. If not, print two with no holes.
• (6) - Fan Grills
• (2*) - Hole Plugs if printing all panels having holes for the power connector or fan controller, fill unused holes with appropriately sized plugs. I printed mine with TPU.
• (1*) - 12.2mm diameter grommet if needed for reinforcing power connector inside wall. May need to adjust hole diameter.

*Optional

Construction is relatively straightforward. Parts are connected with printed connectors and stiffeners. I used CA glue with activator as my adhesive. My process (see photos for details):

1. Connect one side of the panels (top, center, base) and then the other with panel connectors and adhesive.  The connectors may be a snug fit. Elephant foot compensation and/or deburring the edges may be required.
2. Connect the bases. Align the bases and center the base support under the seam and glue. Then glue three of the stiffeners in the indented sections on the base. (Note: The indents don't perfectly align, but the stiffeners should fit inside them.)
3. Install the fan grilles, fans, power connector and fan control. 
   1. Use the angled holes at the sides of the panel connectors for cable management
   2. Attach fans to harness. Remove the connector at the end of the fan harness, strip the (+) and (-) wires.  Connect (+) and (-) wires to the appropriate part of the fan controller. 
   3. Attach the power supply connector with (+) and (-) wires from the power connector to the fan controller.
4. Connect the two top cover halves with the center connector and reinforce with two stiffeners. Add weatherstripping to the inside of the cover.
5. Install filters.