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RESIDENTIAL GAS AND ELECTRIC WATER HEATER
SERVICE HANDBOOK
A.O. Smith Water Products Company Training Department
©2002 Ashland City, Tennessee
4
General Section – continued
% Thermal Efficiency
= (GPH X 8.25 X Temp. Rise X 1.0) divided by BTU/H Input
BTU Output
= GPH X 8.25 X Temp. Rise X 1.0
GPH
= (BTU/H Input X % Eff.) divided by (Temp. Rise X 8.25)
One cubic foot
of Natural Gas contains about 1000 BTU of heat.
One “therm”
is equal to 100,000 BTU
One cubic foot
of Propane Gas contains about 2500 BTU of heat.
One gallon
of Propane gas contains about 91,250 BTU of heat.
One pound
of Propane gas contains about 21,600 BTU of heat.
One pound of gas pressure is equal to 27.7 inches water column pressure
Inches of Water Column X .036091 = PSI
Inches of Water Column X .073483 = Inches of Mercury (Hg.)
Centimeters = Inches X 2.54
MM (millimeters) =Inches X 25.4
Meters = Inches X .0254
Doubling the diameter of a pipe will increase its flow capacity (approximately) 5.3 times.
CONSTRUCTION:
Tank
is constructed of steel.
The inside of the tank is constructed of a
glass lining
bonded to the steel. This prevents water
to metal contact and rusting of the tank.
An
anode rod
will be installed within the tank. The hex-head plug end of the anode is visible on
the top of the water heater. This metal rod offers secondary protection of the tank against
corrosion where the application of glass is not possible (threaded tank openings). These areas
will have small areas of water to metal contact.
All water heaters will contain at least
one thermostat
(to operate the heater) and
one high
limit
(to prevent water temperatures approaching the “steam” level).