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SUF SERVICE HANDBOOK
QUESTIONS AND ANSWERS
Technical Training Department State Water Heaters
STC-077
38 Ashland City, Tennessee © 2004
QUESTIONS AND ANSWERS
Q. How much electrical power is required for a SUF water heater?
A. The SUF models draw approximately 5.0 Amps Max.
Q. When should SUF’s be delimed?
A. Many variables affect the lime build up process including:
• Water temperature — the amount of lime accumulation during the same period of time will be
nearly 2 times great if water is stored at 140 degrees F than at 120 degrees F. A 180° setting
may accumulate seven times more lime — in a period of time — than at 140° setting.
• Volume of water — the more gallons flowing through the SUF, the more rapid the
accumulation.
• Hardness — the harder the water the quicker lime build up occurs. 1 to 3.5 grains per gallons
is “soft”, 3.5 to 7 grains per gallon is “moderate”, 7 to 10.5 grains per gallons is “hard” and
10.5+ grains per gallon is “very hard”. (An aspirin is about 5 grains. One grain is equal to 17.1
parts per million.)
A. Deliming should be done when a slight rumbling or popping sound is detected when the main
burner is on. Check for accumulation through the clean-out opening.
Q. What effect will lime build-up have on the SUF water heater?
A. One eighth inch of scale buildup on the heat exchanger may reduce efficiency as much as
22%; a ¼ inch buildup, as much as 38%.
Less efficient heat transfer means more heat exchanger expansion/contraction stress and pre-
mature leakage.
Because the heat transfer to the water is made through a (relatively) small diameter, coil type
exchanger tube, expansion and contraction as well as the shape of the exchanger greatly
reduces buildup on the heat transfer surface. The bottom of the tank should be checked for
dislodged accumulation.
Q. Anode rods (4) provide additional protection against corrosion. When should these be
replaced?
A. When large gouges or pits appear in the anodes, replace them.
Q. How often should the anodes be inspected?
A. Approximately every six months.