Air Purifier - Silent

This is a silent and compact DIY air purifier built using 5 × 120 mm computer fans, 2 × 16×24×4 MERV-13 charcoal filters, and 3D-printed fan shrouds to improve airflow efficiency.

The design uses a dual-filter intake (parallel filters) with fans mounted on two faces of the enclosure. The fans pull air through the filters and exhaust clean air out through the shrouds.

Key Features
5× 120 mm PC fans (quiet and energy efficient)
2× 16×24×4 MERV-13 filters for high airflow with good filtration
3D-printed fan shrouds (slightly expanding) to improve airflow and reduce dead zones
Compact footprint compared to a traditional 4-filter CR box

Why the 3D Printed Shrouds?
The shrouds are designed as short, slightly expanding diffusers. These help:
improve airflow by reducing turbulence
recover airflow lost near the fan hub
increase overall efficiency of the fans

Performance
This setup provides strong airflow while maintaining good filtration, making it well-suited for medium-sized rooms. The use of 4" filters reduces pressure drop compared to thinner filters, allowing the PC fans to perform more effectively.

Notes
Fans are configured to pull air through the filters
All seams should be well sealed to prevent bypass airflow
Could be upgraded to automated fan speed control.
I suggest you check out my air quality monitor using SEN54. https://www.thingiverse.com/thing:7330189

Shopping List (As an Amazon Associate I earn from qualifying purchases)
Filters - https://amzn.to/3PBP9Pb
Tape - https://amzn.to/4so0XTJ
Computer Fans - https://amzn.to/4stdeq8
Fan Controller - https://amzn.to/3NuRURT
Extension cable - https://amzn.to/4d4zBgH
Foam board - https://amzn.to/4sCwrFG

To build this unit, you will need a way to cut the foam and tape. A hobby knife or similar tool works well (example: https://amzn.to/4bKMTN3).

1. Cut the foam panels
   Cut each piece of foam slightly smaller than the side dimensions so the edges can tuck neatly into adjacent panels without sticking out. You can trim as needed during assembly for a better fit.
2. Assemble the fan shrouds
   Use tape along the inside seams to secure the shrouds together.
3. Mount the fans
   Attach the fans to the shrouds, making sure they are oriented to exhaust outward through the shroud.
4. Attach shrouds to filters
   Tape the fan shroud assemblies to the appropriate filter faces. Ensure the airflow arrows on the filters point inward, so air is pulled through the filters and exhausted out through the fans.
5. Secure the filter walls
   Use tape on the inside, outside, or both to attach the foam panels to the filters and form the enclosure. Leave the smallest foam wall off until last.
6. Route wiring
   Drill or cut a small hole in one panel to pass the power cable through. Connect the fans and ensure all wiring is neatly routed and secured so it cannot contact the fan blades during operation.
7. Final assembly
   Mount electrical connectors to one of the interior walls before installing the final foam panel.

Safety Notice:
The fan blades are exposed in this design. Use caution, as contact with the blades may cause injury. This build is not recommended for environments where children or pets may have access.
If needed, a simple safety guard can be added by attaching a mesh or screen over the fan shrouds (e.g., using hot glue or fasteners).