Rheem Optima Owner's Manual And Installation Instructions page 28

CONNECTIONS – PLUMBING
PIPE SIZES
To achieve true mains pressure operation, the cold water line to the water
heater should be the same size or bigger than the hot water line from the water
heater.
The pipe sizing for hot water supply systems should be carried out by persons
competent to do so, choosing the most suitable pipe size for each individual
application. Reference to the technical specifications of the water heater and
local regulatory authority requirements must be made.
TEMPERATURE PRESSURE RELIEF VALVE
The temperature pressure relief valve is shipped either under the top flap of the
water heater carton or behind the front cover or in a plastic bag attached to the
water heater. The temperature pressure relief valve must be fitted before the
water heater is operated. Before fitting the relief valve, make sure the probe
has not been bent. Seal the thread with Teflon tape - never hemp. Make sure
the tape does not hang over the end of the thread.
Screw the valve into the correct opening (refer to the installation diagram on
page 25) leaving the valve outlet pointing downwards. Do not use a wrench on
the valve body - use the spanner flats provided. A copper drain line must be
fitted to the temperature pressure relief valve (refer to "Relief Valve Drain" on
page 27).
EXPANSION CONTROL VALVE
Local regulations may make it mandatory to install an expansion control valve
(ECV) in the cold water line to the water heater. In other areas, an ECV is
required if the saturation index is greater than +0.4 (refer to "Water Supplies"
on page 11).
The expansion control valve must always be installed after the non return valve
and be the last valve installed prior to the water heater (refer to diagram on
page 27). A copper drain line must be fitted to the expansion control valve
(refer to "Relief Valve Drain" on page 27).
The valve must be insulated with closed cell polymer insulation or similar
(minimum thickness 9 mm) and the insulation installed so as not to impede the
operation of the valve. The insulation must be weatherproof and UV resistant if
exposed.
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