Buy a carbon pre-filter pad for your homemade air carbon filter. This material is popularly used in humidifiers and air conditioning units. It is generally available in small, medium or large packs. Although the actual size you may need primarily depends on your ventilation set-up, as a general guide for this project, you need at least a pack that can be cut in a size of 8 inches by 24 inches.
Cut your carbon pre-filter pad to the required size of 8 inches by 24 inches. This can generally fit most ventilation set-ups.
Cut your aluminum screen to a square measuring 12 inches on each side. You may also use chicken mesh or any similar material as a substitute for aluminum.
Attach the carbon pre-filter pad on the middle of the aluminum screen. Allot 2 inches coming out of each end where you can connect your assembly to the duct piece.
Connect the aluminum screen with the carbon pre-filter to the duct piece. Use duct tape for the attachment. Hold them firmly and make a few wraps until the attachment is stable enough to hold its own weight. It is best to secure it with duct tape every few inches and make sure you cover up the ends of the screen to avoid any little strands of metal from poking out.
Wrap the pre-filter pad onto the aluminum screen and seal it up by placing more duct tape around the filter’s edges. Put tape on any gaps for final sealing; however, put tape only over the edges as air doesn’t flow through the tape. Improper sealing of the edges with tape may pose problems with your homemade filter’s air flow.
Attach your new air carbon filter to the exhaust using a 4-inch square duct and 4-inch ventilation end-cap, then slide it onto your vent. Secure the filter assembly with tape.