Rheem PVR50-80 (NAT) warranty Thermal Expansion, Water Supply Connections, Typical Installation

Thermal Expansion

Determine if a check valve exists in the inlet water line. Check with your local water utility company. It may have been installed in the cold water line as a separate back flow preventer, or it may be part of a pressure reducing valve, water meter or water softener. A check valve located in the cold water inlet line can cause what is referred to as a “closed water system”. A cold water inlet line with no check valve or back flow prevention device is referred to as an “open” water system.

As water is heated, it expands in volume and creates an increase in the pressure within the water system. This action is referred to as “thermal expansion”. In an “open” water system, expanding water which exceeds the capacity of the water heater flows back into the city main where the pressure is easily dissipated.

A “closed water system”, however, prevents the expanding water from flowing back into the main supply line, and the result of “thermal expansion” can create a rapid and dangerous pressure increase in the water heater and system piping. This rapid pressure increase can quickly reach the safety setting of the relief valve, causing it to operate during each heating cycle. Thermal expansion, and the resulting rapid, and repeated expansion and contraction of components in the water heater and piping system can cause premature failure of the relief valve, and possibly the heater itself. Replacing the relief valve will not correct the problem!

The suggested method of controlling thermal expansion is to install an expansion tank in the cold water line between the water heater and the check valve (see illustration below). The expansion tank is designed with an air cushion built in that compresses as the system pressure increases, thereby relieving the over pressure condition and eliminating the repeated operation of the relief valve. Other methods of controlling thermal expansion are also available. Contact your installing contractor, water supplier or plumbing inspector for additional information regarding this subject.

IMPORTANT: Do not apply heat to the HOT or COLD water connections. If sweat connections are used, sweat tubing to adapter before fitting adapter to the cold water connections on heater. Any heat applied to

Water Supply Connections

Refer to the illustration below for suggested typical installation. The installation of unions or flexible copper connectors is recommended on the hot and cold water connections so that the water heater may be easily disconnected for servicing if necessary. The HOT and COLD water connections are clearly marked and are 3/4” NPT on all models. Install a shut-off valve in the cold water line near the water heater.

the cold water supply fittings will permanently damage the dip tube.

Vacuum Relief Valve

(Not Supplied)

If required, install per local codes

and valve manufacturer’s

instructions.

NOTICE: The National Fuel Gas Code (NFGC) mandates a manual gas shut-off valve: See (NFGC) for complete instructions. Local codes or plumbing authority requirements may vary from the instructions or diagrams provided and take precedent over these instructions.

Typical Installation

Vent connector to

chimney Union

Heat trap 6” minimum

Hot water outlet to fixtures

Water Heater Jacket

Temperature and pressure relief valve

Manual gas shut-off

To gas supply

Ground joint union

Sediment trap

Cap

Thermostatic gas valve

Jacket door

Auxiliary catch pan

Drain Pan Pipe to suitable drain.

Pitch up 1/4” per foot

Draft hood

	Anode
	Union
Shut-off	Heat trap
	6” minimum
valve
	To cold water
	supply
Thermal expansion	Shut-off valve
tank (if required)
Drain	Relief valve discharge
	line to suitable open
valve
	drain.

Combustion Air

Inlet Openings

6” Air gap

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