Return Air Plenum Material Question

[emo65170]

Hello,

The AC system in my house is of the kind where the air handler shares a space next to the water heater atop a centrally located return air plenum. The house was built in the early 80s and the return air plenum is simply a 2x4 framed box with drywall on all sides. Note: Although the plenum is retangular, the air handler sits on the opposite side from the return grill.

If you remove the return grill (not a filter grill) you can see the backside of the drywall and the 2x4s of the frame. The floor of the plenum is simply the bare concrete slab of the house. The filter sits in a slot directly under the air handler. In the corners of the frame a lot of dust and fuzzy stuff has collected, due to the turbulence of the air in those areas, I imagine.

I was thinking about installing/lining the inner walls of the plenum to keep the airflow smooth and clean.

Some materials I've considered are Formica high pressure laminate, FRP(Fiberglass Reinforced Plastic), Hardi fiber cement backerboard, Aluminum Flashing, Moisture resistant (green faced) drywall. Each material has pros and cons regarding installation/fabrication complexity, moisture resistance, durability, flammability etc...

What are your thoughts on the best material to line a plenum?

Thanks!

Ed

[Rcb2875]

Simply for ease of use and insulation purposes.. Simple ol' duct board. Just build it to match the old dimensions but off the floor a bit.