Domestic Hot Water Piping - Rheem 199,000 Btu/hr User Manual

NOTE
See Domestic Hot Water
Warnings on page 1-25.
Tankless
Water Heater
DHW DCW
Figure 25: Overview of piping
connections
WARNING
- Bacteria growth can develop
in domestic hot water tanks
and indirect water heaters if the
minimum water temperature is
not set high enough to prevent
its growth.
- Failure to support the boiler
fitting with a second wrench
while tightening field piping may
lead to boiler damage.
1-26
TANKLESS WATER HEATER 199

1.7.2 Domestic Hot Water Piping

The domestic water piping connections are located at the bottom of the unit, see
Figure 1b. The connections are
the right side and the hot water outlet is on the left side.
Use two wrenches when tightening field piping onto the boiler. Use one wrench to
hold the boiler fitting still while tightening with another wrench.
An installer supplied pressure relief valve meeting the following requirements must
be installed:
●
Maximum pressure rating of 150 PSI.
●
Minimum capacity of 200,000 Btu/hr.
●
On the domestic hot water outlet prior to any isolation valve.
Installation of a tankless water heater service valve kit with pressure relief valve is
recommended for ease of servicing the DHW coil in the future.
The Tankless Water Heater can be connected to the pressurized 1/2" or larger
domestic cold water supply piping and the domestic hot water piping in the home.
The minimum domestic water pressure required is 40PSI and recommended to be
50PSI or higher. Generating domestic hot water with a water pressure lower than
40PSI reduces the amount of hot water generated and increases the risk of scaling
in the heat exchanger.
The domestic water piping must be installed with isolation valves and flushing taps
installed on both the cold and hot domestic connections.
Thermal expansion of the water in the domestic hot water (DHW) system can
occur without DHW usage such as in DHW Comfort Mode. As the small volume
of DHW in the heat exchanger is heated, it expands in volume and creates an
increase in the pressure within the water system. Check with your local water utility
company to determine if a check valve has been installed in the cold water line. If
a check valve has not been installed, the expanding water volume flows back into
the main, dissipating pressure. If a check valve has been installed, the expanding
water volume will increase the pressure within the homes water system. A DHW
expansion tank is typically not required due to the low volume of DHW in the heat
exchanger. If the pressure increase causes operation of the pressure relief valve, a
DHW expansion tank must be installed.
The cold water inlet includes a filter to prevent contaminants from fouling the
flow sensor and heat exchanger. See maintenance section 4.1.12 for cleaning
procedure.
Graph 1: Water Heater Pressure Drop
" male NPT threads. The cold water inlet is on
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INSTALLATION AND OPERATION INSTRUCTIONS