Heating sizing your ductwork

duckwork-01.jpgTouch on picture to enlarge

Supply pipe as follows to each area
30-48 SF 4” round pipe
50- 80SF 5” round pipe
81-150SF 6” round pipe
If you are more willing to use Flex pipe rather than steel round pipe up size the flex by 1” in diameter because of the resistance in the flex piping.
Using a lot of flex tubing for supply and returns only decreases the quantity of air trying to be moved.
Trunk lines (ductwork, metalwork, etc. has many names) are size according to the supply pipes they are feeding
On any square style duct allow 16” of air for resistance in the ductwork
4” pipe needs 10” of air
5” pipe needs 13” of air
6” pipe needs 16” of air
7” pipe needs 19” of air
If we have a 12”x 8” size duct this will supply 5-6” round pipes, 8-4”, 6-5” or a combination of sizes
If you try to install more pipes than what a trunk line can handle the longest round pipe runs will get little to no air movement.

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