PVC pipe for A/C

[edroelle]

Too large a duct will provide too slow air flow.  Bigger is not necessarily better.   You want to shoot for 800-1100 ft/min air flow velocity.   Cold, air conditioned air, needs velocity.   Air volume in cu. ft/min. divided by duct cross sectional area in sq.ft. gives velocity in ft/min.   

Ed Roelle
Flint, MI

[jjrbus]

When I did my roof air AC install there was an installation manual/booklet that came with the AC. It was very specific about the size of duct to use. Not 6X4 inch or 6 inch dia. but the size was given in square inches  min and max. also vent placement and size and dia/radius of turns.  I belive this is done to provide the proper back pressure for the unit to function properly.  So maximum airflow may not be in your best interest??   I am not a HVAC guy, so the information from the manufacturer may be wrong.

                                                                    Jim

[muddog16]

Call me silly! But I'd use duct work for my system.......but I'm just silly!

[JackConrad]

We used UltraDuct. Great stuff to work with. I cut it with a straight edge and utility knife, creased with a screen spline installation tool and straight edge, folded and taped the seam with aluminum duct tape.    UltraDuct is a layer of high density closed cell foam with a layer of aluminum foild bonded to each side of the foam.  Total thighness is approx. 3/16". This enabled us to make our ducts to the exact specs of the AC manufacturer and is much lighter than PVC. Also easier to make turns when neccessary. 
   We purchased ours from Innovative Energy, Inc, Lowell, IN 800-776-3645.  We picked ours up at there place (4x8 sheets), but they will cut it into 2x4 sheets so it can be shipped via UPS/FedEx.  I dealt with Ron Rado (VP & Gen. Manager)   Jack

[BG6]

The bottom line is that there is no advantage to PVC over other materials, and there are several DISadvantages.

The greatest of these is the addition of a few cubic inches of toxic flammables, distributed from one end of the coach to the other, in a way which ensures the greatest toxic effect if a fire starts, and which will help the fumes and fire spread more rapidly.  One top goal when you design your conversion is to minimize or even remove things which can burn (that's why I used steel studs instead of wood 2x4s).