The duct work size of the CLAYTONS is 20" round. How I came up with that size is according to the calculation from the book posted earlier.
17 (6" round pipe branch runs) X 2 + (2" for 90 degree elbow) + (2" for 90 degree elbow) + (2" for 90 degree elbow) X 8" for the duct = 320sq.in.
17 x 2 = 34 + 2 + 36 + 2 = 38 + 2 + 40 x 8 = 320
The book says,
18" round pipe = 254.46 sq.in.
20" round pipe = 314.16 sq.in.
22" round pipe = 380.13 sq.in.
So, the 20" round pipe fell within the 10% of recomended sizing for solid fuel duct sizing. At first, I was leery of sizing the system that way. Taking all the square smaller ductulator sized duct out. But I new it really didn't work too well with the hand fired CLAYTON, let alone the forced gas and air conditioning so far. So I thought, what the heck, I can always put it back the way it was. From the 20" round plenum it narrows to two 12" branches and one 16" branch and to another 12" branch from the 16". All being sized from the calculation above. Well guess what. It has out performed anything I could of imagined. Even the gas forced air and the air conditioning system works better.
Whoever came up with that calculation sure knows their stuff!!
I'm glad I did it and would recommend any new system or remodel to do the same. Round flows better, is quieter, weighs less, cost less to install and in my oppinion, easier to install.
The only down side is that it doesn't fit into space as easily and if your the tin knocker, you you won't make as much money on the fabrication.
Thanks for the nomination. DOUG