Boiler Distribution Pipe Sizing
Hydronic GPM = Q / (500 × delta-T), the smallest copper / steel / PEX size at or below the velocity ceiling, velocity, Hazen-Williams head loss per 100 ft, and pump head at the run length. Per ASHRAE Systems and Equipment 2020 Ch. 13.
Formula and source
GPM = Q / (500 × delta-T) (hydronic water energy balance). Velocity (ft/s) = GPM / (2.448 × d_in²). The smallest standard inner diameter whose velocity is at or below the ceiling is recommended. Head loss = Hazen-Williams (C = 150 copper/PEX, 130 steel); pump head = head per 100 ft × run length / 100.
ASHRAE Systems and Equipment 2020 Chapter 13 (hydronic heating) by name; Bell & Gossett / Taco system-design velocity limits by name. Hazen-Williams (1905) public domain.
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