SERVICE
INFORMATION
GUIDE
FORMULAS & FACTS
BTU (British Thermal Unit) is the heat required to raise 1 pound of water 1°F
1 BTU = 252 cal = 0.252 kcal
1 cal = 4.187 Joules
BTU X 1.055 = Kilo Joules
BTU divided by 3,413 = Kilowatt (1 KW)
FAHRENHEIT CENTIGRADE
32 0
41 5
To convert from Fahrenheit to Celsius:
(°F – 32) x 5/9 or .556 = °C.
60.8 16
120.2 49
140 60
180 82
212 100
One gallon of 120°F (49°C) water
weighs approximately 8.25 pounds.
Pounds x .45359 = Kilogram
Gallons x 3.7854 = Liters
% of hot water =
(Mixed Water Temp. – Cold Water
Temp.) divided by (Hot Water Temp.
– Cold Water Temp.)
% thermal efficiency =
(GPH recovery X 8.25 X temp. rise X
1.0) divided by BTU/H Input
BTU output (Gas) =
GPH recovery x 8.25 x temp. rise x 1.0
Linear expansion of pipe
– in inches per 100 Ft.
– 1 grain per gallon = 17.1 Parts Per million
Grain
(measurement of water hardness)
BTU output (Electric) =
BTU Input (Not exactly true due
to minimal flange heat loss.)
Capacity of a
cylindrical tank
– 1 ⁄2 diameter (in inches)
x 3.146 x length. (in inches)
Divide by 231 for gallons.
Doubling the diameter
of a pipe will increase its flow
capacity (approximately)
5.3 times.
TEMP °F RISE STEEL COPPER
0.38˝ 0.57˝
°
50
1.14˝
.076˝
°
00
1
125° .092˝ 1.40˝
1.75˝
1.15˝
°
150
FORMULAS & FACTS
TC-092
FORMULAS & FACTS
GPH (Gas) =
(BTU/H Input X % Eff.) divided by
(temp. rise x 8.25)
GPH (Electric) =
(KW x 3413) divided by
(temp. rise x 8.25) or (KW x 414)
divided by (temp rise.)
KW required =
(GPH X 8.25 X temp. rise)
divided by 3413 or
(GPH x Temp. rise) divided by 414
1 KW =
3413 BTH = 4.1 GPH @ 100° temp.
rise or 4.6 GPH @ 80° temp. rise
Meters = Inches x .0254
Centimeters = Inches X 2.54
mm (millimeters) = Inches x 25.4
One boiler horsepower (BHP) =
33,475 BTU
One cubic foot of Natural Gas
contains about 1000 BTU of heat.
One “therm” is equal to
100,000 BTU (100 CU. FT.)
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.)
One pound per sq. in.
= 16 oz per sq. in.
Water expands
approximately 2% in volume
for a 100°F temperature rise
(from 40°F to 140°F)
Water confined
to a storage tank or piping
system, when subjected
to a temperature rise of 10°F
(increasing from 75° to 85°),
increases pressure from
50 psi to 250 psi.
One cubic foot of Propane Gas
contains about 2500 BTU of heat.
Water capacity of copper tubing per foot
1
TUBING SIZE
3
⁄2
⁄4 111⁄2 23
g/ft type L .012 .025 .044 0.92 .161 .354
TC-092
FORMULAS & FACTS
COMMON TERMS
Draw efficiency is the quantity of hot water available
to the consumer before the outlet water temperature
decreases 25°F. A 40-gallon water heater will typically
provide 70% (28 gallons) within this temperature range.
The burner or elements are allowed to operate during
this test. Incoming, cold water mixes the remaining
stored water below this 25° limitation.
Energy factor is an indicator of the combined thermal efficiency and standby
efficiency of a water heater. The higher the energy factor, the more efficient the
water heater will be.
What Happens
When W
The relationship between water temperature and time to
1
burn normal adult skin.
WATER TIME FOR 1ST TIME FOR PERMANENT BURNS
°F DEGREE BURN (2nd AND 3rd DEGREE)
TEMP.
105 Normal shower temperature
122 1 minute 5 minutes
131 5 seconds 25 seconds
140 2 seconds 5 seconds
ater Is Heated:
2
Water cannot (for all practical purposes) be compressed.
Water expands when it is heated. Approximately .00023% per
3
degree F temperature rise.
This expansion will result in a pressure increase in a “closed” system.
Water confined to a storage tank or piping system will, when subjected
to a temperature rise of 10°F (increasing from 75°F to 85°F) increase
in pressure from 50 psi to 250 psi.
TC-093
COMMON TERMS
COMMON TERMS
The closed system illustrated requires the thermal expansion tank because
of the preceding #2 and #3 facts.
4
Gases in the water will separate from the water as temperature rises.
5
Water boils at 212°F
pressure. At 52 psi gauge pressure, water would not boil until it
exceeded 300° F.
6
Minerals in the water will separate from the water as temperature is added.
This may lead to a much faster scaling rate in the tank.
Ex: 10 grains hardness; 2700 gallons of hot water per day.
Water stored at 140
160°F in the tank may accumulate 85 lbs. of lime per year.
180°F in the tank may accumulate 135 lbs. of lime per year.
7
Adding heat to water may make it more corrosive.
Water may be 2 times more corrosive at 160°F than at 140°F.
TC-093
Water may be
– at sea level – unless it is contained under
°F in the tank may accumulate 19 lbs. of lime per year.
2 times mor
e cor
osive at 18
r
0°F than at 160°F.
COMMON TERMS
COMMON TERMS
Polarity – Verify that an electrical socket has
correct “polarity.” Verify that the “Neutral”
(typically white on a 120V circuit) wire has
no power to ground and that the “Hot”
(typically black wire on a 120V circuit)
has 115 – 125V to ground.
Watts divided by Volts
= Amps (single phase)
Watts x .557) divided by
(
(Volts) = Amps (3 phase)
For insulating purposes “R” value is a measure of the resistance of a
substance to heat flow.
Recovery rate is the amount of water that is heated to a specific temperature
rise, per hour. An example might be that a water heater has a recovery rate
of 30 gallons of water per hour at 80° F temperature rise.
Thermal efficiency is approximately the percentage of generated BTU
that enters the stored water. A percentage of the total BTU input passes
out through the vent piping.
Volts x amps = watts.
Volts divided by amps
= ohms (resistance)
Temperature rise is the increase in the temperature from its
coldest “inlet” water temperature to the desired hot (outlet) setting.
Typically this is assumed to be 40° entering water; 120° desired
stored water or 80° “temperature rise.”
Standby efficiency is the water heater’s ability to contain heat in the tank.
A minimum of tank water heat loss per hour is desired.
Sample: temperature change per hour = BTU/H loss/square foot of tank surface
“R” value
Water hammer is a concussion of moving water against the sides of a
containing pipe or vessel on a sudden stoppage of flow.
Ex: 1/2 ˝ copper pipe, 5GPM flow (7.2ft/sec.) – stop.
Pressure rise of approximately 412 psi
3/4˝ copper pipe, 5GPM flow (3.3ft/sec) – stop.
Pressure rise of approximately 188 psi
TC-093
COMMON TERMS
A. O. SMITH TRAINING CENTER
106 Adkisson Street
Ashland City, TN 37015
www.hotwater.com
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