Instructions / Assembly
46
INSTALLATION INSTRUCTIONS
Water Quality
Water Supply
!
CAUTION:
This water heater MUST ONLY be used with the 
following water supply conditions to prevent 
product damage and operation failure.
Clean, potable water free of corrosive chemicals, sand, 
dirt, or other contaminates�
Inlet water temperatures above 32°F (0°C), but not 
exceeding 120°F (49°C)�
DO NOT reverse the HOT and COLD water connections�
DO NOT connect this heater to water lines previously 
used for space heating� All water piping and components 
shall be suitable for potable water�
With recommended water quality (See chart above)�
Thermal Expansion
A thermal expansion tank will be required if 
the water heater is installed in a system with a 
recirculation or storage tank. This prevents damage 
to the heater, related piping, and the relief valve.
NOTICE: 
Replacing the relief valve will not correct the 
problem!
The expansion tank is designed with a built-in air 
cushion that compresses as the system pressure 
increases. This relieves the over-pressure condition 
and eliminates the repeat operation of the relief 
valve.
For other approved methods of thermal expansion, 
contact an installing contractor, water supplier, or 
plumbing inspector.
Water Supply Connections
!
CAUTION:
IMPORTANT—DO NOT apply heat to the HOT or 
COLD water connections. If sweat connections are 
used, sweat tubing to the adapter before fitting 
the adapter to the water connections on the water 
heater. Any heat applied to the water supply fittings 
will permanently damage the internal components 
of the water heater.
NOTICE:
In cold environments, ice can accumulate in the 
water heater’s connectors. Plug in the water heater 
power cord for approximately 10 minutes before 
making these connections. This will melt any ice 
buildup. 
Plumbing should be carried out by a qualified 
plumbing contractor in accordance with local codes.
Only use approved plumbing materials.
To allow the full flow capacity, it is recommended 
to keep water inlet and outlet pipes 3/4-in. (1.9-cm) 
diameter or larger. 
To conserve energy and to prevent freezing, 
insulate both COLD and HOT water supply lines. 
DO NOT insulate the pressure-relief valve.
Chart for Recommended Water Quality Levels
pH
(Total Dissolved 
Solids) TDS
Free Carbon 
Dioxide (CO
2
)
Total 
Hardness
Aluminum Chlorides Copper Iron Manganese Zinc
6�5–8�5 Up to 500 mg/L Up to 15 mg/L
Up to 
200 mg/L
0�05 to 
0�2 mg/L
Up to 
250 mg/L
Up to 
1�0 mg/L
Up to 
0�3 mg/L
Up to 
0�05 mg/L
Up to 
5 mg/L
Cited reference: National Secondary Drinking Water Regulations
Plumbing
Water quality must be taken into account when 
installing and maintaining the water heater. Water 
conditions outside of the levels specified below affect 
and may damage the water heater. Please note that 
the limited warranty provided with the water heater 
does not cover defects, malfunctions or failures 
resulting from water conditions that are not in 
accordance with the specifications in the table 
below.
If you nonetheless install this water heater where the 
water conditions are not within the levels specified in 
the table below, Rheem recommends that you take the 
following steps:
• Install a water treatment device or water softener at 
the same time as the original installation of the water 
heater. Rheem offers a water treatment accessory that 
can be installed with the water heater. (See below).
• Flush the water heater’s heat exchanger regularly.  
Rheem offers a flush kit and isolation valves to help 
remove scale build up. (See below)
Accessory Kit Replacement Filter Tankless Flush Kit Tankless Isolation Valve
AllClear Water Treatment Kit RTG20251 RTG20252 
RTG20124 RTG20220AB
Scale Prevention Device RTG20246 RTG20247
Accessory part numbers listed below� See Parts and Accessories Catalog for more information�










