4.7 Water Heating Requirements    

All of the requirements for service hot water that apply to nonresidential occupancies are mandatory measures.  There are additional requirements  for high-rise residential, hotels and motels which must also comply with the Residential Standards §150.1(c)8. which are described below, as well as in the Residential Compliance Manual.

There are no acceptance requirements for water heating systems or equipment, however, high-rise residential, hotels and motel water heating systems must meet the distribution system eligibility criteria for that portion of the system that is applicable.


Figure 4-21 – Service Water Heating Flowchart


4.7.1    Service Water Systems Mandatory Requirements

A.   Efficiency and Control


Any service water heating equipment must have integral automatic temperature controls that allow the temperature to be adjusted from the lowest to the highest allowed temperature settings for the intended use as 'listed in Table 2, Chapter 49 of the ASHRAE Handbook, HVAC Applications Volume.

Service water heaters installed in residential occupancies need not meet the temperature control requirement of §110.3(a)1

B.   Multiple Temperature Usage


On systems that have a total capacity greater than 167,000 Btu/h, outlets requiring higher than service water temperatures as 'listed in the ASHRAE Handbook, HVAC Applications Volume shall have separate remote heaters, heat exchangers, or boosters to supply the outlet with the higher temperature. This requires the primary water heating system to supply water at the lowest temperature required by any of the demands served for service water heating. All other demands requiring higher temperatures should be served by separate systems, or by boosters that raise the temperature of the primary supply.

C.   Controls for Hot Water Distribution Systems

Service hot water systems with a circulating pump or with electrical heat trace shall include a control capable of automatically turning off the system when hot water is not required. Such controls include automatic time switches, interlocks with HVAC time switches, occupancy sensors, and other controls that accomplish the intended purpose.

D.   Public Lavatories

Lavatories in public restrooms must have controls that limit the water supply temperature to 110°F. Where a service water heater supplies only restrooms, the heater thermostat may be set to no greater than 110°F to satisfy this requirement; otherwise controls such as automatic mixing valves must be installed.

E.   Storage Tank Insulation

Unfired water heater storage tanks and backup tanks for solar water heating systems must have:

1.   External insulation with an installed R-value of at least R-12; or

2.   Internal and external insulation with a combined R-value of at least R-16; or

3.   The heat loss of the tank based on an 80 degree F water-air temperature difference shall be less than 6.5 Btu per hour per ft². This corresponds to an effective resistance of R-12.3.

F.   Service Water Heaters in State Buildings

High-rise residential buildings constructed by the State of California shall have solar water heating systems. The solar system shall be sized and designed to provide at least 60 percent of the energy needed for service water heating from site solar energy or recovered energy. There is an exception when buildings for which the state architect determines that service water heating is economically or physical infeasible. See the Compliance Options section below for more information about solar water heating systems.

G.   Pipe Insulation Thickness

There are updated pipe insulation thickness requirements applicable to nonresidential water heating pipes. For pipes with conductivity ranges within those specified in Table 120.43-A of the Standard, the nominal pipe diameters grouping ranges are changed, as well as the thickness of insulation required for each pipe diameter range.  The table is repeated below for ease of reference:



(in Btu-inch per hour per square foot per °F)



1 and less

1 to <1.5

1.5 to < 4

4 to < 8

8 and larger


Space heating, Hot Water systems (steam, steam condensate and hot water) and Service Water Heating Systems (recirculating sections, all piping in electric trace tape systems, and the first 8 feet of piping from the storage tank for nonrecirculating-recirculating systems)

Above 350








































Space cooling systems (chilled water, refrigerant and brine)









Below 40









H.   Systems with Recirculation Loops

Service water systems that have central recirculation distribution  must include all of the following mandatory features.  The intent of these measure is to optimize performance and allow for lower cost of maintenance. These requirements are applicable to nonresidential occupancies as well as high-rise residential and hotel/motel systems.

Air Release Valves


The constant supply of new water and the operation of pump create the possibility of the pumps cavitation due to air in the water. Cavitation is the formation of bubbles in the low pressure liquid on the suction side of the pump. The cavities or bubbles will collapse when they pass into the higher regions of pressure, causing noise, and vibration, which may lead to damage to many of the components. 'In 'addition there is a loss in capacity and the pump can no longer build the same head (pressure). Ultimately this impacts the pumps’ efficiency and life expectancy.

Cavitation shall be minimized by either the installation of an air release valve or mounting the pump vertically. The air release valve must be located no more than 4 ft from the inlet of the pump. The air release valve must be mounted on a vertical riser with a length of at least 12 inches.

Backflow Prevention


Temperature and pressure differences in the water throughout a recirculation system can create potentials for backflows. This can result in cooler water from the bottom of the water heater tank and water near the end of the recirculation loop flowing backwards towards the hot water load and reducing the delivered water temperature..

To prevent this from occurring, the Standards require that a check valve or similar device be located between the recirculation pump and the water heating equipment.

Equipment for Pump Priming/Pump Isolation Valves


A large number of systems are allowed to operate until complete failure simply because of the difficulty of repair or servicing. Repair labor costs can be reduced significantly by planning ahead and designing for easy pump replacement when the pump fails.  Provision for pump priming and pump isolation valves help reduces maintenance costs.

To meet the pump priming equipment requirement, a hose bib must be installed between the pump and the water heater. 'In addition, an isolation valve shall be installed between the hose bib and the water heating equipment. This configuration will allow the flow from the water heater to be shut off, allowing the hose bib to be used for bleeding air out of the pump after pump replacement.

The requirement for the pump isolation valves will allow replacement of the pump without draining a large portion of the system. The isolation valves shall be installed on both sides of the pump. These valves may be part of the flange that attaches the pump to the pipe. One of the isolation valves may be the same isolation valve as in item C.

Connection of Recirculation Lines


Manufacturer’s specifications should always be followed to assure optimal performance of the system. The cold water piping and the recirculation loop piping should never be connected to the hot water storage tank drain port.

Backflow Prevention in Cold Water Supply


The dynamic between the water in the heater and the cold water supply are similar to those in the recirculation loop. Thermosyphoning can occur on this side of this loop just as it does on the recirculation side of the system. To prevent this, the Standards require a check valve to be installed on the cold water supply line. The valve should be located between the hot water system and the next closest tee on the cold water supply line. Note that the system shall comply with the expansion tank requirements as described in the California Plumbing Code Section 608.3.


4.7.2    Mandatory Requirements Applicable to High-Rise Residential and Hotel/Motel

'In 'addition to the mandatory requirements 'listed above, there are mandatory requirements that will apply to water heating systems for hotels, motels and high-rise residential buildings only.  All of these requirements are tied to the mandatory requirements in §150.0 for residential occupancies.  Depending on weather the water heating system has a central system or uses individual water heaters will change weather the mandatory features that are 'listed above apply.

A.   Storage tank Insulation requirements


For buildings that use individual water heaters or instantaneous water heaters for each unit with a supplemental storage tank R-12 insulation must be installed if the water heaters efficiency is equal to the federal minimum standard.  For unfired supplemental tanks R-12 must be installed if the internal insulation of the unfired tank is less than R-16.

B.   Water piping insulation thickness and conductivity


All domestic hot water system piping conditions 'listed below, whether buried or unburied, must be insulated and the insulation thickness shall be selected based on the conductivity range in Table 120.3-A and the insulation level shall be selected from the fluid temperature range based on the thickness requirements in TABLE 120.3-A

The first five feet of pipe of hot and cold water from the storage tank must be insulated.  In the case of a building with a central distribution system this requirement means that the cold supply line to the central water heater would have to be insulated.  For building with central recirculation systems the hot water supply to each unit must be insulated to meet this requirement and the kitchen piping insulation requirement.

Any pipe in the distribution system that is ¾ inch or larger must be insulated.  This includes pipe in the central distribution system and in the distribution system serving the individual units.

Any piping that is associated with a recirculation loop must be insulated.  If the domestic hot water heater system serving the dwelling unit uses any type of recirculation insulation of the entire length of the distribution loop would be required.   Insulation would also be required in the case of a dwelling unit with a combined hydronic system that uses any portion of the domestic hot water loop to circulate Insulation would not be required on the branches or twig serving the point of use.

All hot water pipe from the water heater or source of hot water for each dwelling unit to the kitchen must be insulated. 

All underground hot water piping, all piping from the water heater to kitchen sinks and dishwashers and all non-recirculating hot water piping of 3/4" diameter or greater are mandatory measure as specified in §150.0(j).

'In 'addition, all piping below grade must be installed in a waterproof and non-crushable casing or sleeve that allows for installation, removal and replacement of the enclosed pipe and insulation.  The internal cross-section or diameter of the casing or sleeve shall be large enough to allow for insulation of the hot water piping.  Piping below grade that serves any island sinks or other island fixtures or appliances may be insulated with 1/2 inch wall thickness insulation.

Note that there are exceptions.  Pipe insulation may be omitted where hot water distribution piping is buried within attic, crawlspace or wall insulation, as described below: In attics and crawlspaces the insulation shall completely surround the pipe with at least 1 inch of insulation and the pipe shall be completely covered with at least 4 inches of insulation further away from the conditioned space. In walls, the insulation must completely surround the pipe with at least 1 inch of insulation. If burial within the insulation does not meet these specifications, then this exception does not apply, and the section of pipe not meeting the specifications must be insulated.

      The last segment of piping that penetrates walls and delivers hot water to the sink, appliance does not require insulation. 

      Piping that penetrates framing members shall not be required to have pipe insulation for the distance of the framing penetration. Piping that penetrates metal framing shall use grommets, plugs, wrapping or other insulating material to assure that no contact is made with the metal framing. Insulation shall butt securely against all framing members.  

      Piping below grade that serves any island sinks or other island fixtures or appliances may be insulated with 1/2 inch wall thickness insulation.

4.7.3    Prescriptive Requirements – Only applicable to High-Rise Residential and Hotel/Motel

For water heating recirculation systems for high-rise residential and hotel/motel buildings, the code actually references back to the Residential Prescriptive requirements. The following paragraphs recap these requirements.

A.   Solar Water Heating


Solar water heating is prescriptively required for water heating systems serving multiple dwelling units, whether it is a motel/hotel or high-rise multifamily building. The minimum SSF is dependent on the climate zone: 0.20 for CZ 1 through 9, and 0.35 for CZ 10 through 16. The regulations does not limit the solar water heating equipment or system type, as long as they are SRCC certified and meet the orientation, tilt and shading requirement specified in RA 4.4. Installation of a solar water heating system exempts multifamily buildings from needing to set aside solar zone for future solar PV installation (§110.10(b)1B). The following paragraphs offer some high-level design considerations for multifamily building solar water heating systems.

A high-priority factor for solar water heating system design is component sizing. Proper sizing of solar collectors and solar tank ensures that the system take full advantage of the sun’s energy while avoiding the problem of overheating. While the issue of freeze protection has been widely explored (development of various solar water heating system types is a reflection of this evolution), the issue of overheating is often not considered as seriously as it should be, especially for climate conditions with relatively high solar insolation level such as California. This is especially critical for multifamily-sized systems, due to load variability.

To be conservative, the highest SSF requirement called for by the 2013 Title 24 at 35%. Stakeholders further suggested that industry standard sizing for an active system is 1.5 ft2 collector area per gallon capacity for solar tank. For more detailed guidance and best practices, there are many publicly available industry design guidelines. Two such resources developed by/in association with government agencies are Building America Best Practices Series: Solar Thermal and Photovoltaic Systems , and California Solar Initiative – Thermal: Program Handbook.Because of the new solar water heating requirement and prevalence of recirculation hot water systems in multifamily buildings, it is essential to re-iterate the importance of proper integration between the hot water recirculation system and the solar water heating system. Industry stakeholders recommended the recirculation hot water return to be connected back to the system downstream of the solar storage tank. This eliminates the unnecessary wasted energy used to heat up water routed back from the recirculation loop that may have been sitting in the solar water tank if no draw has occurred over a prolonged period of time.

Another design consideration is the layout and placement of collectors and solar tank. The idea here, similar to the discussions on recirculation system design in Section 5.3.3, is to minimize the length of plumbing, thus reducing pipe surface areas susceptible to heat loss and piping materials needed. This calls for the shortest feasible distance between the collectors themselves; furthermore, since solar tanks are typically plumbed in series with, just upstream of the conventional/auxiliary water heating equipment, the distance between collectors and solar tank should also be as short as practically possible.

B.   Dual Recirculation Loop Design


A dual-loop design is illustrated in Figure 4-22.  In a dual-loop design, each loop serves half of the dwelling units. According to plumbing code requirements, the pipe diameters can be downsized compared to a loop serving all dwelling units. The total pipe surface area is effectively reduced, even though total pipe length is about the same as that of a single-loop design. For appropriate pipe sizing guidelines, please refer to the Universal Plumbing Code.

Figure 4-22-Example of a Dual-Loop Recirculation System


Figure 4-22 provides an example of how to implement duel-loop design in a low-rise multi-family building with a simple layout. In this example, the water heating equipment is located in the middle of top floor with each recirculation loop serve exactly half of the building. The recirculation loops are located in the middle floor to minimize branch pipe length to each dwelling units. The figure also illustrates how the solar water heating system and demand control are integrated.

For buildings with complicated layouts, how to create and locate recirculation loops heavily depends on building geometry. In general, the system should be designed to have each loop serving the equal number of dwelling units in order to minimize pipe sizes. For systems serving buildings with distinct sections, e.g. two wings in an “L” shaped building, it is better to dedicate a separate recirculation loop to each of the section. Very large buildings and buildings with more than two sections should consider using separate central water heating systems for each section or part of the building with each water heating systems having dual-loop designs. In all case, simple routing of recirculation loops should be used to keep recirculation pipes as short as possible. Figure 4-22 provides dual-loop recirculation system designs in buildings of complicated shapes.

Figure 4-22 Examples of dual-loop recirculation system designs
in buildings of complicated shapes


Location of water heating equipment in the building also needs to be carefully considered to properly implement the dual-loop design. The goal is to keep overall pipe length as short as possible, as an example, for building in regular shapes, locating the water heating equipment at the center of the building footprint rather than at one end of the building help to minimize the pipe length needed to connect the water heating equipment to the two loops. If a water heating system serves several distinct building sections, the water heating equipment would preferably nest in between these sections.

With the new prescriptive solar water heating requirement this cycle, it is especially important to consider the integration between the hot water recirculation system and the solar water heating system. Based on feedbacks from industry stakeholders, most solar water heating systems are only configured as a pre-heater of the primary gas water heating equipment. In other words, recirculation hot water returns are usually plumbed back to the gas water heating storage tanks, not directly into the solar tank. This means recirculation loop designs should be mostly based on the building layout and are relatively independent of the solar water heating system. On the other hand, gas water heating equipment and solar tank should be located closed to each other to avoid heat loss from pipes connecting the two systems. The preferred configuration is to place both the gas water heating equipment and solar tank on the top floor near the solar collector so that the total system pipe length can be reduced. As noted before, minimizing pipe length help reduced DHW system energy use as well as system plumbing cost.

C.   Demand Recirculation Control

The prescriptive requirement for DHW systems serving multiple dwelling units requires the installation of a demand recirculation control to minimize pump operation. Please note that they are different from the demand control used in single dwelling units. Demand controls for central recirculation systems are based on hot water demand and recirculation return temperatures. The temperature sensor should be installed at the last branch pipe along the recirculation loop.

Any system not meeting these prescriptive requirements must instead meet the Standard Design Building energy budget or must follow the performance compliance method for the building as a whole.

4.7.4   Pool and Spa Heating Systems    

A.   Pool and spa heating systems must be certified by the manufacturer and 'listed by the Energy Commission as having:

1.   An efficiency that complies with the Appliance Efficiency Regulations; and

2.   An on-off switch mounted on the outside of the heater in a readily accessible location that allows the heater to be shut-off without adjusting the thermostat setting; and

3.   A permanent, easily readable, and weatherproof plate or card that gives instructions for the energy efficient operation of the pool or spa, and for the proper care of the pool or spa water when a cover is used; and

4.   No electric resistance heating. The only exceptions are:

a.   'Listed packaged units with fully insulated enclosures and tight fitting covers that are insulated to at least R-6. 'Listed package units are defined in the National Electric Code and are typically sold as self-contained, UL 'Listed spas; or

b.   Pools or spas deriving at least 60 percent of the annual heating energy from site solar energy or recovered energy.

B.   If a pool or spa does not currently use solar heating collectors for heating of the water, piping must be installed to accommodate any future installation. Contractors can choose 3 options to allow for the future addition of solar heating equipment:

1.   Leave at least 36 inches of pipe between the filter and heater to allow for the future addition of solar heating equipment.

2.   Plumb separate suction and return lines to the pool dedicated to future solar heating.

3.   Install built-up or built-in connections for future piping to solar water heating. An example of a built-in connection could be a capped off tee fitting between the filter and heater.

C.   Pool and spa heating systems with gas or electric heaters for outdoor use must use a pool cover. The pool cover must be fitted and installed during the final inspection.

D.   All pool systems must be installed with the following:

1.   Directional inlets must be provided for all pools that adequately mix the pool water.

2.   A time switch or similar control mechanism shall be provided for pools to control the operation of the circulation control system, to allow the pump to be set or programmed to run in the off-peak demand period, and for the minimum time necessary to maintain the water in the condition required by applicable public health standards.


Pool and spa heaters are not allowed to have pilot lights.