Clarifying Codes for Solar Water Heating Systems


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Plumbing codes by state
Plumbing codes by state
Plumbing codes by state

Though still lacking national uniformity, some code requirements for solar water heating (SWH) installations are gaining clarity in 2015.

Unlike PV system requirements, which have significant uniformity due to the use of the National Electrical Code (NEC), SWH requirements vary depending on which code sets are used. Jurisdictions usually adopt one of two primary plumbing and mechanical codes—the Uniform code or the International code (“I-code”). Lack of uniformity leads to significant differences in SWH system requirements between jurisdictions. To identify the requirements for installing a system in your particular area, you will need to know which code(s) are relevant in your jurisdiction. Chances are that you need to follow either the Uniform Plumbing Code (UPC) or the plumbing section of the International Residential Code (IRC). But if you live in New Jersey or Maryland, you need to follow the National Standard Plumbing Code.

While 2015 code changes will not resolve this lack of uniformity, they will provide more explicit code requirements for SWH systems installed in states that have adopted the I-codes. This is a result of collaboration between the International Code Council (ICC) and the Solar Rating & Certification Corporation (SRCC), which officially merged in 2014. This relationship has resulted in a significant reworking of the Solar Energy Systems chapter of the IRC, which applies to one- and two-family dwellings.

The requirements of Chapter 23 in the 2012 IRC were fairly limited and touched mostly on requirements from other portions of the IRC that deal with the installation of water heaters, mechanical equipment, and roofing. The major SWH-specific requirements in the 2012 IRC ensure freeze protection for systems that will experience temperatures below 32°F, and verify that collectors are listed and labeled.

Confusion in the 2012 IRC

While the SWH requirements of the 2012 I-codes are few, those that are included have caused confusion among the code community. For instance, 2012 IRC M2301.2.8 stipulates that “valves shall be installed to allow the solar collectors to be isolated from the remainder of the system.” If interpreted literally, this could result in isolating the heat source of the system—the solar collectors—from the relief valve, which could lead to excessive pressure and catastrophic failure if the valves were ever closed. 2012 IRC M2301.2.3 recognizes this to an extent by requiring that “relief valves shall be installed in sections of the system so that a section cannot be valved off or isolated from a relief device.” This vaguely written section contradicts M2301.2.8. It would seem to require two relief valves in the solar loop of a system—one for each portion of the system that can be isolated. A second relief valve would be unnecessary in many SWH systems, where the only pressure hazard is on the collector side of the isolation valves, due to the heat they generate.

Another section of the 2012 IRC demonstrates a limited understanding of SWH systems. 2012 IRC P2902.5.5 stipulates that “the potable water supply to a solar system shall be equipped with a backflow preventer.” An exception is given for systems where the solar collectors directly heat potable water. This requirement has caused confusion in some jurisdictions that have interpreted “the potable water supply to a solar system” to mean the potable water supply to the water heater.

This portion of the 2012 IRC is an example of taking a requirement for a similar technology—in this case, boilers—and applying it to SWH systems. With boilers, this requirement refers to a direct connection between the potable water and the mechanical piping. This occurs when an autofill valve is installed to provide makeup water in a boiler. Standard SWH systems do not have this type of direct connection between the mechanical piping—the solar loop—and the potable water supply. This misunderstanding has led to inappropriate requirements that put local code officials in a difficult position if they have a limited understanding of SWH systems. In some states, this misunderstanding has led to a restrictive interpretation of the code that increases the complexity and cost of systems without providing a tangible health or safety benefit. This has significantly limited the installation of code- compliant systems in these areas.

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