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Code, Section IV or CSA B51, as applicable. Select a relief valve with
a discharge NOT less than the boiler input, and a pressure rating NOT
exceeding the working pressure of any component in the system.
A. O. Smith supplies a 125 psi relief valve for hot water supply systems
and 50 psi relief valve for space heating application.
An ASME rated temperature and pressure relief valve must be installed
on each and every water storage tank in a hot water supply system.
The storage tank temperature and pressure (T & P) relief valve must
comply with the applicable contruction provisions of the Standard
for Relief valves and Automatic Gas Shutoff Devices for Hot Water
Supply Systems, Z21.22 - CSA 4.4. The T & P valve must be of the
automatic reset type and not embody a single-use type of fusible
plug, cartridge or linkage.
The T & P relief valve should have a maximum temperature rating
of 100°C (210°F), a pressure rating NOT exceeding the lowest
rated working pressure of any system component, and a discharge
capacity exceeding the total input of the water boilers supplying
water to the storage tank.
Locate the T & P relief valve (a) in the top of the storage tank or (b)
in the side of the tank on centerline within upper 6 inches from the
top of the tank. See Figures 28 to 33, Pages 34 to 38. Tapping shall
be threaded in accordance with the latest version of the Standard for
Pipe Threads, General Purpose (inch), ANSI/ASME B.120.1.
Mark location with a class III Label. See ANSI Z21.10.1, Part 1,
Marking, See CAN/CSA B149.
TANK TEMPERATURE CONTROL
The water temperature in the storage tank is controlled by the Tank
Temperature Control. The sensing element is mounted inside the
hot water storage tank.
DANGER
HOT WATER TEMPERATURES REQUIRED FOR AUTOMATIC
DISHWASHER AND LAUNDRY USE CAN CAUSE SCALD BURNS
RESULTING IN SERIOUS PERSONAL INJURY AND/OR DEATH.
THE TEMPERATURE AT WHICH INJURY OCCURS VARIES
WITH THE PERSON’S AGE AND TIME OF EXPOSURE. THE
SLOWER RESPONSE TIME OF CHILDREN, AGED OR DISABLED
PERSONS INCREASES THE HAZARDS TO THEM. NEVER ALLOW
SMALL CHILDREN TO USE A HOT WATER TAP, OR TO DRAW
THEIR OWN BATH WATER. NEVER LEAVE A CHILD OR DISABLED
PERSON UNATTENDED IN A BATHTUB OR SHOWER.
The tank temperature control is adjustable from 100°F (37.7°C) to
220°F (104.4°C). It is recommended that lower water temperatures
be used to avoid the risk of scalding. It is further recommended, in all
cases, that the water temperature be set for the lowest temperature
which satises the user’s hot water needs. This will also provide the
most energy efcient operation of the water heater and minimize
scale formation.
THE WATER HEATER SHOULD BE LOCATED IN AN AREA WHERE
THE GENERAL PUBLIC DOES NOT HAVE ACCESS TO SET
TEMPERATURES. SETTING THE WATER TEMPERATURE AT
120°F (49°C) WILL REDUCE THE RISK OF SCALDS. Some states or
provinces require settings at specic lower temperatures. Below you
will nd listed the approximate time-to-burn relationship for normal
adult skin. Valves for reducing point-of-use temperature by mixing
cold and hot water are available. Also available are inexpensive
devices that attach to faucets to limit hot water temperatures. Contact
a licensed plumber or the local plumbing authority.