DIY Basic Carbon Filter

Needed Materials

• Activated carbon granules suitable for air scrubbing
• Wood to make a frame, e.g. 35x75mm pine
• Piece of MDF or plywood
• Fly screen mesh
• Fence mesh
• U-shaped nails
• Screws
• Glue

Directions

This is a flat panel carbon air filter that I made for about $30 (not including carbon). It's not as compact as a round filter but it's easy to make and works perfectly.

This is just a frame to hold a bed of carbon granules on flyscreen mesh, with the other side of the frame sealed by MDF. My first idea was just to use fly screen on a wooden frame, but the granules are heavier than you'd think (about 0.6kg/L). So I used some rigid fencing mesh to support the fly screen.

1) Construct frame of required length and width from wood
2) Glue a piece of fly screen to one side of the frame
3) Nail a piece of fencing mesh over the top of the fly screen (U-shaped nails are good for this)



4) The other side is covered by a piece of MDF or plywood, which is screwed on so that it can be removed later



5) The fan or a duct starter can be mounted onto the MDF side. I covered the hole with another piece of fly screen to keep the granules in, in case I forget that it is open or I drop it.



6) Fill the frame with a layer of carbon and seal it up



The fencing mesh prevents the fly screen from drooping. This would cause all the granules to collect in the middle and leave a gap around the edges. The fly screen is also glued to the frame at the edges to prevent granules leaking out.

The fencing mesh is expensive at about $80 for a huge sheet (1.2x2.4m), but you can substitute that for something else. I found some in my backyard (no it wasn't a piece of my fence ).

From what I've read most commercial filters use a 20-25mm thick bed of carbon. The ideal bed thickness will depend on your fan, frame size and required air flow. I just used 25mm bed thickness and that seemed to work first go, leaving no smell but still giving good airflow even with a 150mm axial fan.

Where do you get activated carbon and how much does it cost?
There are many grades depending on what you are trying to filter. I bought carbon specifically for odor filtering (specification '4x8 mesh, 208C' whatever that means) from an industrial chemical supplier for $8/kg but I had to buy a 25kg bag. There are people on ebay selling granules for $10/kg but I'm not sure if it is the right type for filtering air.

Rejuvenating carbon
My first attempt at a filter is still going strong after a year, but if the carbon starts to let smell through, people who use carbon to filter distilled alcohol claim that it can be rejuvenated by heating it up red hot in the microwave (this boils off the molecules it has captured apparently).

Have fun!