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napper 07-26-2008 08:44 PM

Toughest duct work I can get?
I have two supply lines under the house in crawl space that I need to replace. They were originally made of duct board and about to fall apart!

Short of stainless steel what choices do I have? It is damp in the summer due to condensation so I need it to be rust resistant too. I saw some "externally rated" duct work on a package unit a work. Looked like some tar paper heavy coated duct board. It was completlely exposed to the elements. What is this stuff?

Could I make it out of duct board and then enclose with treated plywood? Ducts are 16" x 16" square.

Bondo 07-28-2008 07:45 PM


You could probably fashion them out of FRP panels,... Fiberglass sheeting...

I'd think that Ventilating the crawl space would do more for you though,....
Isn't your whole house rotting away on you,..??

napper 07-28-2008 10:04 PM

Crawl space is Fully ventilated! Part of the problem. House is up on cresote poles with about 4 ft of space under house. Very humid in South Alabama and you get condensate on ducts. I need something tougher than duct board.

What are FRP panels?

coolmen 07-29-2008 07:35 AM

use steel and insulat VERY well

nap 07-29-2008 10:56 AM

typical steel duct work is made from galvanized steel. Unless you buy the cheapest stuff around or have some really odd conditions, this would be very rust resistant (very little is rust proof) and last the life of the building.

then, insulate that which will prevent the condensation on the duct work.

Bondo 07-29-2008 05:14 PM


What are FRP panels?

This Stuff,......

From these people......

napper 07-29-2008 07:48 PM

Would FRP panels be suitable for duct construction?

javan 07-30-2008 10:52 AM

Usually FRP and other plastic ductwork is usually best suited for harsh environments where caustic conditions exist. Typically it is used as exhaust D/w for the industrial applications. BUT you can use it for home HVAC.

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