Code Considerations for Solar Water Heating Systems

The installers of solar water heating systems have to navigate a range of plumbing and mechanical codes, which sometimes seem to be at odds with each other.

Installation of solar water heating (SWH) systems requires significant expertise in a number of trades. Installers need to know carpentry—critical for mounting solar collectors—as well as electrical systems, necessary for installing system controls. They also need a thorough grounding in plumbing and heating systems to properly integrate SWH equipment with standard water and space heating systems.

Each of these trades has a set of requirements that installers must follow to ensure code compliance. In many jurisdictions, this requires SWH installers to be knowledgeable about specific portions of the local building, plumbing, mechanical, energy conservation and electrical codes.

Among jurisdictions in the US, some code adoption is relatively uniform. The International Residential Code (IRC), International Building Code (IBC), International Energy Conservation Code (IECC) and National Electrical Code, for instance, are dominant. Some variation exists because each jurisdiction decides which edition of a code to adopt, but the contrast in requirements for these codes is not as stark as it is for plumbing and mechanical codes.

There are two primary plumbing codes in the US: the Uniform Plumbing Code (UPC) and the International Plumbing Code (IPC). Most jurisdictions have adopted the UPC or IPC. Exceptions include states that have adopted unique state plumbing codes, including Louisiana and Massachusetts, and states that have adopted the National Standard Plumbing Code (NSPC), such as Maryland and New Jersey.

While the International Mechanical Code (IMC) and the Uniform Mechanical Code (UMC) share some similarities, they differ significantly in their treatment of SWH systems. In addition, the national mechanical codes have variations that can create confusion and inconsistency in local requirements.

In this article, I explore differences among the plumbing and mechanical codes, and clarify some of the more confusing code requirements that impact SWH integration professionals. I also explore and explain portions of the international codes and the Uniform Solar Energy Code (USEC) that have posed a challenge for installers, designers and building inspectors.

Unique Characteristics of Solar Heating Systems

Plumbing and mechanical codes must be broad enough to accommodate all types of heating systems, including gas and oil boilers, ground-source heat pumps, radiant heating distribution, electric water heaters and solar heating systems. Sometimes the industry introduces new techniques or technologies faster than the code organizations can respond. For instance, some SWH system installers have begun to use corrugated stainless steel tubing (CSST), a material that the major mechanical codes have yet to address.

Committees of volunteers, each with specific expertise, create the plumbing and mechanical codes. A plumbing code committee must have members who are knowledgeable in topics such as water supply, sanitary drainage and plumbing fixtures. The code reflects the expertise and foresight of these individuals. If committee members have limited experience with a particular technology, they may approve requirements without full consideration of whether they apply to all the technologies that the specific code governs. The resulting code requirements may be too restrictive or may be irrelevant for systems that operate differently from the norm. This has been the case in several US jurisdictions, where applying requirements for standard hydronic systems to SWH systems has created onerous installation procedures.

There are two significant differences between antifreeze solar heating systems and the majority of standard hydronic systems: First, most hydronic systems have an automatic fill valve that adds water to the system to maintain its pressure, while many SWH systems do not. Second, unlike solar heating systems, most standard hydronic heating systems automatically shut off the heat sources when temperatures exceed design parameters.

Without an automatic fill valve, antifreeze and drainback solar heating systems contain a fixed amount of liquid. If a component fails or if an overpressure situation occurs, it is a singular occurrence that the introduction of more fluid into the system does not exacerbate. This is an important difference, as hydronic heating systems with make-up water supplied via an automatic fill valve can experience numerous overpressure events if they are not immediately identified.


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