This appendix presents a simple method for estimating the head loss of piping paths or circuits constructed of smooth tubing, such as copper tubing or PEX.
The head loss of a piping path or circuit can be determined using Formula B-1.
Formula B-1
$$ H_L = (acl)f^{1.75} $$
$H_L$ = Head loss of circuit (ft of head)
$a$ = a factor that depends on the average water temperature
in piping (see Figure B-1)
$c$ = a factor determined by the type and size of tubing in
the circuit (see Figure B-2)
$l$ = total equivalent length of the circuit (ft)
$f$ = flow rate (gpm)
$1.75$ = an exponent of flow rate
The values of “a” read from Figure B-1 should be based on the average water temperature in the piping. Thus, for a recirculation loop with a supply temperature of 130ºF and a return temperature of 120ºF, the value of “a” would be determined at the average fluid temperature of 125ºF.