User note: Code change proposals to this chapter will be considered by the IRC – Plumbing and Mechanical Code
    Development Committee during the 2015 (Group A) Code Development Cycle. See explanation on page iv.


    M2301.1 General.

    This section provides for the design, construction, installation, alteration and repair of equipment and systems using thermal solar energy to provide space heating or cooling, hot water heating and swimming pool heating.

    M2301.2 Design and installation.

    The design and installation of thermal solar energy systems shall comply with Sections M2301.2.1 through M2301.2.13.

    M2301.2.1 Access.

    Solar energy collectors, controls, dampers, fans, blowers and pumps shall be accessible for inspection, maintenance, repair and replacement.

    M2301.2.2 Collectors and panels.

    Solar collectors and panels shall comply with Sections M2301.2.2.1 and M2301.2.2.2.

    M2301.2.2.1 Roof-mounted collectors.

    The roof shall be constructed to support the loads imposed by roof-mounted solar collectors. Roof-mounted solar collectors that serve as a roof covering shall conform to the requirements for roof coverings in Chapter 9 of this code. Where mounted on or above the roof coverings, the collectors and supporting structure shall be constructed of noncombustible materials or fire-retardant-treated wood equivalent to that required for the roof construction.

    M2301.2.2.2 Collector sensors.

    Collector sensor installation, sensor location and the protection of exposed sensor wires from ultraviolet light shall be in accordance with SRCC 300.

    M2301.2.3 Pressure and temperature relief valves and system components.

    System components containing fluids shall be protected with temperature and pressure relief valves or pressure relief valves. Relief devices shall be installed in sections of the system so that a section cannot be valved off or isolated from a relief device. Direct systems and the potable water portion of indirect systems shall be equipped with a relief valve in accordance with Section P2804. For indirect systems, pressure relief valves in solar loops shall comply with SRCC 300. System components shall have a working pressure rating of not less than the setting of the pressure relief device.

    M2301.2.4 Vacuum relief.

    System components that might be subjected to pressure drops below atmospheric pressure during operation or shutdown shall be protected by a vacuum-relief valve.

    M2301.2.5 Piping insulation.

    Piping shall be insulated in accordance with the requirements of Chapter 11. Exterior insulation shall be protected from ultraviolet degradation. The entire solar loop shall be insulated. Where split-style insulation is used, the seam shall be sealed. Fittings shall be fully insulated.


    1. 1.Those portions of the piping that are used to help prevent the system from overheating shall not be required to be insulated.

    2. 2.Those portions of piping that are exposed to solar radiation, made of the same material as the solar collector absorber plate and are covered in the same manner as the solar collector absorber, or that are used to collect additional solar energy, shall not be required to be insulated.

    3. 3.Piping in thermal solar systems using unglazed solar collectors to heat a swimming pool shall not be required to be insulated.

    M2301.2.6 Protection from freezing.

    System components shall be protected from damage resulting from freezing of heat-transfer liquids at the winter design temperature provided in Table R301.2(1). Freeze protection shall be provided by heating, insulation, thermal mass and heat transfer fluids with freeze points lower than the winter design temperature, heat tape or other approved methods, or combinations thereof.

    Exception: Where the winter design temperature is greater than 32°F (0°C).

    M2301.2.7 Storage tank sensors.

    Storage tank sensors shall comply with SRCC 300.

    M2301.2.8 Expansion tanks.

    Expansion tanks in solar energy systems shall be installed in accordance with Section M2003 in solar collector loops that contain pressurized heat transfer fluid. Where expansion tanks are used, the system shall be designed in accordance with SRCC 300 to provide an expansion tank that is sized to withstand the maximum operating pressure of the system.

    Exception: Expansion tanks shall not be required in drain-back systems.

    M2301.2.9 Roof and wall penetrations.

    Roof and wall penetrations shall be flashed and sealed in accordance with Chapter 9 of this code to prevent entry of water, rodents and insects.

    M2301.2.10 Description and warning labels.

    Solar thermal systems shall comply with description label and warning label requirements of Section M2301.2.11.2 and SRCC 300.

    M2301.2.11 Solar loop.

    Solar loops shall be in accordance with Sections M2301.2.11.1 and M2301.2.11.2.

    M2301.2.11.1 Solar loop isolation.

    Valves shall be installed to allow the solar collectors to be isolated from the remainder of the system.

    M2301.2.11.2 Drain and fill valve labels and caps.

    Drain and fill valves shall be labeled with a description and warning that identifies the fluid in the solar loop and a warning that the fluid might be discharged at high temperature and pressure. Drain caps shall be installed at drain and fill valves.

    M2301.2.12 Maximum temperature limitation.

    Systems shall be equipped with means to limit the maximum water temperature of the system fluid entering or exchanging heat with any pressurized vessel inside the dwelling to 180°F (82°C). This protection is in addition to the required temperature- and pressure-relief valves required by Section M2301.2.3.

    M2301.2.13 Thermal storage unit seismic bracing.

    In Seismic Design Categories D0, D1 and D2 and in town-houses in Seismic Design Category C, thermal storage units shall be anchored in accordance with Section M1307.2.

    M2301.3 Labeling.

    Labeling shall comply with Sections M2301.3.1 and M2301.3.2.

    M2301.3.1 Collectors and panels.

    Solar thermal collectors and panels shall be listed and labeled in accordance with SRCC 100 or SRCC 600. Collectors and panels shall be listed and labeled to show the manufacturer’s name, model number, serial number, collector weight, collector maximum allowable temperatures and pressures, and the type of heat transfer fluids that are compatible with the collector or panel. The label shall clarify that these specifications apply only to the collector or panel.

    M2301.3.2 Thermal storage units.

    Pressurized thermal storage units shall be listed and labeled to show the manufacturer’s name, model number, serial number, storage unit maximum and minimum allowable operating temperatures and pressures, and the type of heat transfer fluids that are compatible with the storage unit. The label shall clarify that these specifications apply only to the thermal storage unit.

    M2301.4 Heat transfer gasses or liquids and heat exchangers.

    Essentially toxic transfer fluids, ethylene glycol, flammable gases and flammable liquids shall not be used as heat transfer fluids. Heat transfer gasses and liquids shall be rated to withstand the system’s maximum design temperature under operating conditions without degradation. Heat exchangers used in solar thermal systems shall comply with Section P2902.5.2 and SRCC 300.

    Heat transfer fluids shall be in accordance with SRCC 300. The flash point of the heat transfer fluids utilized in solar thermal systems shall be not less than 50°F (28°C) above the design maximum nonoperating or no-flow temperature attained by the fluid in the collector.

    M2301.5 Backflow protection.

    Connections from the potable water supply to solar systems shall comply with Section P2902.5.5.

    M2301.6 Filtering.

    Air provided to occupied spaces that passes through thermal mass storage systems by mechanical means shall be filtered for particulates at the outlet of the thermal mass storage system.

    M2301.7 Solar thermal systems for heating potable water.

    Where a solar thermal system heats potable water to supply a potable hot water distribution system, the solar thermal system shall be in accordance with Sections M2301.7.1, M2301.7.2 and P2902.5.5.

    M2301.7.1 Indirect systems.

    Heat exchangers that are components of indirect solar thermal heating systems shall comply with Section P2902.5.2.

    M2301.7.2 Direct systems.

    Where potable water is directly heated by a solar thermal system, the pipe, fittings, valves and other components that are in contact with the potable water in the solar heating system shall comply with the requirements of Chapter 29.