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Appendices
Reference Guide for Water Heating
One US gallon of fresh water weighs 8.333 lb.
Water expands 4.34% heated from 40
o
to 212
o
F.
1 BTU = Amount of heat required to raise the temperature of 1 lb. of
water 1
o
F.
Recovery GPH = KW x 3412
(Electric) 8.33 x ΔT
Recovery GPH = Input x Efficiency
(Gas) 8.33 x ΔT
Req. BTU Input = Water Heater Capacity x 8.33 x ΔT
% Efficiency
First Hour Draw (FHD)
FHD = (Storage x % Efficiency) + Recovery
% of hot and cold water needed to be mixed to obtain a desired
temperature
Hot water percentage = M-C
H-C
Cold water percentage = H-M
H-C
Water C = Cold Water Temperature
H = Hot Water Temperature
M = Mixed Water Temperature
% Efficiency = GPH x 8.33 x Temp. Rise
BTU/Hr. Input
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