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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.
The relationship between water temperature and time to
burn normal adult skin.
WATER TIME FOR 1ST TIME FOR PERMANENT BURNS
TEMP.
°F DEGREE BURN (2nd AND 3rd DEGREE)
105 Normal shower temperature
122 1 minute 5 minutes
131 5 seconds 25 seconds
140 2 seconds 5 seconds
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What Happens
When W
ater Is Heated:
Water cannot (for all practical purposes) be compressed.
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TC-093
COMMON TERMS
Water expands when it is heated. Approximately .00023% per
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.
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