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jjrbus 05-30-2010 07:31 AM

Duct board
It seems my current duct work is too small. 12X12, outside dimension, made from duct board. Duct board comes in 4X8 sheets so to use it to make a larger duct would result in a lot of waste. Does board come in different sizes, is there a better product to use?

beenthere 05-30-2010 08:12 AM

No, it 4X8X8 is it.

Not as much waste as you may think. 1 sheet of 1" think duct board will only make 2 pieces of 12X12(inside dimension, outside would be 14X14) duct. With only 8" of waste. If you were to use 1" think duct board, it would make 2-12X12 with no waste.

fpeftw 05-30-2010 08:13 PM

Ductboard also comes in 4x10 from our supply shop.

beenthere 05-30-2010 10:26 PM


Originally Posted by fpeftw (Post 449039)
Ductboard also comes in 4x10 from our supply shop.

LOL... I got carried away with my typing.
It should have been 4X4X10

jjrbus 05-31-2010 07:47 AM

Now it makes sense!! Thanks for bringing that up fpeftw. I'm thinking 3 14x8 from the first piece adding a 14x8 from the second piece:laughing:

My current 10x10 inside dimension would be 100 square inch. A 12x12 ID would be 144 sq in a gain of 44%. Would that be large enough for a 2 ton system??


fpeftw 05-31-2010 08:16 AM

That should be adequate for a 2 ton system. How long of a run are you making?

jjrbus 05-31-2010 08:47 AM

I am still in the thinking planning stage, so not sure. Plus add I know nothing about HVAC! I would like to learn enough to either DIY or make an educated choice for contractor to hire.

What would be an optimal length for a 12X12 duct with a 2 ton unit?

Thanks for the response JIm

beenthere 05-31-2010 08:53 AM

Min 8X20, or 10X16. ID.

jjrbus 05-31-2010 09:02 AM

Now I see a lot of waste useing duct board. Does duct come premade in these size's?? What would be an optimal or maximum length??

beenthere 05-31-2010 09:08 AM

Is no one optimal length.

Some companies carried pre-made. It is 8" high, and you can usually get it in up to 28" width, and they are all 4 foot long.

The ID is determined by the total equivalent length of the duct system.

jjrbus 05-31-2010 10:17 AM

Thanks beenthere, I found an online duct fabricator manual, makes things a lot clearer.

I'm sure you don't need it :) but may help someone else.

I am confident I could do the actual fabrication and installation of the duct work. The design of the system seems like it should be left to someone who knows what they are doing. Do you know of any online design services??

Thanks again JIm

beenthere 05-31-2010 10:33 AM

No I don't.
Lot of them just use a .1" friction rate, no matter how long the duct is. And thats not the right way.

Can you make a drawing of how your duct is now. And how you want to change it.
Then we could give you advise on what will and won't work. And what can be done to make it better.

jjrbus 05-31-2010 01:30 PM

Yes I can, will take some time. JIm

beenthere 05-31-2010 01:41 PM

No problem.

jjrbus 06-06-2010 12:21 AM

3 Attachment(s)
Here is a floor plan, old setup and beginnings of new set up. Old plan has air handler on east end of house, I believe it would be better on the west end of house. Then I have many questions.
You suggested 8X20 or 10X16 duct. 10X16 looks better for me. The old duct is connected to the Air handler by flex. Could I still do that? Could I use large flex for entire warm air return??
I'm doing this in a trussed attic with a 30 inch height at peak, so space is at a premium.

Opps. 12X8 in floorplan is size of registers. 1st or top drawing is present duct. 2nd or bottom is the proposed one.

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