Rheem 491 Owner's Manual And Installation Instructions page 28

Off-Peak or Time Controlled Electricity Supply
A single or twin element electric water heater connected to an Off-Peak electricity
supply should not be installed as part of a circulated hot water flow and return
system in a building. The benefits of the Off-Peak electricity supply will be
significantly reduced.
If a circulated flow and return system is required, it is necessary to install a
secondary water heater supplied from the Off-Peak electric water heater. The
flow and return lines connect to the secondary water heater, not the Off-Peak
electric water heater. The secondary water heater makes up for the pipe heat
loss in the flow and return system and must be able to provide a hot water outlet
temperature of at least 60°C.
Note: The thermostat or preset outlet temperature of the secondary water heater
must always be set to maintain a temperature of at least 60°C in the hot water
flow and return line, including making up pipe heat losses in the system.
Refer to the Circulated Hot Water Flow and Return – Off-Peak Electric Water
Heater diagram on page 288.
Circulated Hot Water Flow and Return System
Off-Peak Electric Water Heater
LEGEND
REDUCING HEAT LOSSES
The cold water line to and the hot water line from the water heater must be
insulated in accordance with the requirements of Clauses G12 and H1 of the
New Zealand Building Code and AS/NZS 3500.4. The insulation must be
weatherproof and UV resistant if exposed.
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