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Gas Boiler Distribution Pipe Sizing
Weil McClain Gas Boiler CGM 140,000 btu
Existing system has 2 zones each with circulators
I have temporarily added a radiant zone which is added on the end of the 1st floor loop (as an initial - worked out nicely as far as transferring warm thru the floor, it’s a staple up app application).
I want to make the radiant lop a separate loop w/ circ pump.
My Question related to the primary piping out of the boiler.
Existing condition: is 1-1/4” immmediatly reduced down to 1” black iron pipe to the air scoop. 1” inch copper to the 1st branch (which is ¾” – baseboards), then ¾” copper to the second branch (which is also ¾” – baseboards).
The radiant loop is 5/8” pex. Right now its only 1 loop. But I plan to add a manifold to feed 2 – 5/8” loops.
I wondering if the initial piping out of the boiler should be upgraded to 1-1/4 pipe to feed1st and 2nd branches, then use 1” to feed radiant (which will ultimately feed 2 -5/8 pex loops – maybe even more)
I realize this thinking is more along the lines of how a domestic water system would be piped which is supplied under a constant pressure.
I understand that pipe size in a closed loop hydronic heating system is sized based on principals of thermodynamics and heat transfer.
The heat loss analysis for the house = 80,000 btus (at 20 deg drop, flow rate =8-9 gpm
1st Floor (which includes all radiant loops) = 50,000 btus (at 20 drop, flow rate = 5-6 gpm)
If the pipes are based on flow velocities (2 to 4 ft per second)
Main pipe supply from boiler could be 1” for 9gpm
1st floor supply could be ¾” for 6 gpm
According to this the existing system OKAY to support the additional radiant loops
I’m just wondering if there are any other considerations pro/cons to changing the pipe sizes.
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