69
Appendices
Reference Guide for Water Heating
• 11 BTUs are required to raise 1 gallon of water 1
o
F at 70% efficiency
(gas)
• 3,412 BTUs equal 1 kilowatt hour (KW)
• 1 KW will raise 410 gallons of water 1
o
F at 100% efficiency
• 1 BTU x 0.293 = watts
• 1 KW = 1000 watts
• 2.42 watts are required to raise 1 gallon of water 1
o
F
1 KW will raise 10.25 gallons of water 40
o
F at 100% efficiency
1 KW will raise 6.8 gallons of water 60
o
F at 100% efficiency
1 KW will raise 5.1 gallons of water 80
o
F at 100% efficiency
1 KW will raise 4.1 gallons of water 100
o
F at 100% efficiency
Formula for mixing hot water
M-C
H-C
Where M = mixed water temperature; C = cold water temperature;
H = hot water temperature
For example: How much of a shower is hot water and how
much is cold water?
My shower temperature is 105
o
F, my water heater thermostat is
set on 120
o
F and the cold water inlet temperature is 50
o
F.
105 – 50 = 55
120 – 50 = 70
This formula for mixing hot water is important when explaining a NOT
ENOUGH HOT WATER trouble call and the water heater is functioning
properly.
= 79% of the shower is 120
o
hot water
= Percent of hot water required to produce desired mixed
temperature
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