RESIDENTIAL GAS AND ELECTRIC WATER HEATER
SERVICE HANDBOOK
A.O. Smith Water Products Company
Training Department
©
2002
Ashland City, Tennessee
18
STANDARD RESIDENTIAL ELECTRIC WATER HEATER SERVICE GUIDELINES
Construction
See “General Section” for features common to both gas and electric models.
Miscellaneous
:
Amperage
(Amps) (1 phase)
= Watts
divided by Volts
Amperage
(3 phase) = (Watts X .577) divided by Volts
KW
Required
= (GPH X 8.25 X Temp. Rise X 1.0) divided by (3413)
Ohms
= Volts divided by Amperes
One kilowatt
is equal to 1000 watts
One kilowatt
is equal to 3,413 BTU
Recovery Rate
= (KW X 3413) divided by (Temp. Rise X 8.25)
Rise (F
°
)
= (KW X 3413) divided by (GPH X 8.25)
Supply
electrical fusing
or breakers should be sized at least 125% of expected heater
amperage.
Water weighs
8.25 pounds per gallon at 120
°
F (49
°
C).
% of Hot
water = (Mixed temp. – Cold) divided by (Hot temp. – Cold)
Heating element(s)
This style water heater will have
one or two electric, heating
elements immersed in the tank.
One element will always be
located low in the tank; a second
element is commonly located
down about 1/3 of the tank height from the top of the tank. These elements will seldom
be wired to operate at the same time. (If they operate at the same time, amperage draw
doubles, wire gauge size increases, fuse size increases and little is gained in heat
recovery.)
