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Solar Thermal Bypass Valve


Install a code-compliant (UPC, IRC and IMC) valve assembly (solar bypass valve) on the cold water feed of the existing water heater to be used to connect the solar storage tank (see Figure 1). The solar bypass valve should be capped and labeled as an RERH component. Space requirements and layout for solar water heating and photovoltaic system components should be taken into account early in the design process. 

Solar bypass plumbing detail.
Figure 1. Solar bypass plumbing detail.


The EPA Renewable Energy Ready Home (RERH) Solar Water Heating checklist states:

“3.4. Install a solar bypass valve on the cold water feed of the water heater (cap and label both ends).”

Additional Notes:

Most solar water heating systems will require the installation of a separate hot water storage tank. The solar bypass valve makes future connections to this storage tank simple and affordable without having to drain the home’s existing plumbing system. The solar bypass valve should be installed on the cold-water feed of the existing water heater and should be configured in the following manner (see Figure 1):

  1. Install two “T” fittings in the “Cold Water Inlet” pipe that supplies cold water to the existing water heater.
  2. Install shut-off valves on each of the “T” fittings and one in the main pipe between the two “T” fittings.
  3. Stub-off and cap the two open-ended shut-off valves to prevent leakage should the valves be accidentally opened.
  4. Wrap a 3” x 1” label around each bypass valve so the text is visible and upright (if possible).  Each label should read, “Renewable Energy Ready Home Solar Thermal Bypass Valve.”

Builders should be aware that many municipal building codes now require that a backflow valve and pressure tank be installed on the cold water feed. A professional plumber should do this work.
Also worth considering, but not defined by this specification, is the installation of a floor drain. 

See the guides Utility Room Space, Mounting Surface for Pumps and Gauges, Solar Plumbing and Wiring Chase, and Architectural Drawing for more information about the Renewable Energy Ready Home (RERH) Solar Hot Water procedures.

Contributed by:

Pacific Northwest National Laboratory 

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References and Resources*
U.S. Environmental Protection Agency
Publication Date
The RERH specifications and checklists take a builder and a project design team through the steps of assessing a home’s solar resource potential and defining the minimum structural and system components needed to support a solar energy system.
*For non-dated media, such as websites, the date listed is the date accessed.
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