Service water heating requirements applicable to nonresidential occupancies are mandatory measures; non-school buildings must also meet prescriptive high-capacity water heating system requirements. Multifamily buildings, hotels, and motels, must also comply with the Energy Code§160.4 and §170.2(d), described below.
There are no acceptance requirements for water heating systems or equipment. However, central water heating systems serving multifamily, hotel and motel buildings must meet the distribution system eligibility criteria for that portion of the system that is applicable.
§110.3(a)&(b)
Any service water heating equipment must meet all efficiency requirements under the Appliance Efficiency Regulations (Title 20) and 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 3, Chapter 50 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
For systems with 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.
Systems serving healthcare facilities and clinics, which are covered by California Plumbing Code Section 613.0, shall instead follow the requirements of that section.
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.
Systems serving healthcare systems are exempted from this requirement.
Unfired water heater storage tanks and backup tanks for solar water heating systems must have one of the following:
1. External insulation with an installed R-value of at least R-3.5.
2. Internal and external insulation with a combined R-value of at least R-16.
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 sq ft. This corresponds to an effective resistance of R-12.3.
Service water systems with central recirculation distribution must include all of the following mandatory features. The intent of these measures is to optimize performance and allow for lower cost of maintenance. These requirements are applicable to nonresidential occupancies as well as multifamily and hotel/motel systems.
The constant supply of new water and leaks in system piping or components during normal operation of the pump may introduce air into the circulating water. Entrained air in the water may also contribute to increased cavitation, the formation of vapor bubbles in liquid on the low pressure (suction) side of the pump. The vapor bubbles generally condense back to the liquid state after they pass into the higher-pressure side of the pump. Cavitation contributes to a loss of head pressure and pumping capacity, may produce noise and vibration in the pump, and may result in pump impeller corrosion, all of which impacts the pumps’ efficiency and life expectancy.
Entrained air and cavitation should be minimized by the installation of an air release valve. The air release valve must be located no more than 4 feet from the inlet of the pump, and must be mounted on a vertical riser with a length of at least 12 inches. Alternatively, the pump shall be mounted on a vertical section of the return piping.
Temperature and pressure differences in the water throughout a recirculation system can create potentials for backflows, resulting 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 Energy Code requires that a check valve or similar device be located between the recirculation pump and the water heating equipment.
§110.3(c)5 C&D
Many systems are allowed to operate to complete failure due to the difficulty of repair or servicing. Repair labor costs can be reduced significantly by planning ahead and designing for easy pump replacement. Provisions for pump priming and pump isolation valves help reduces maintenance costs.
To meet the pump priming equipment requirement, a hose bibb must be installed between the pump and the water heater. In addition, an isolation valve shall be installed between the hose bibb and the water heating equipment. This configuration will allow the flow from the water heater to be shut off, allowing the hose bibb to be used for bleeding air out of the pump after 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 §110.3(c)5C.
Manufacturer specifications should always be followed to assure optimal system performance. The cold-water piping and the recirculation loop piping should never be connected to the hot water storage tank drain port.
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 the loop just as it does on the recirculation side of the system. To prevent this, the Energy Code requires 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. The system shall comply with the expansion tank requirements of California Plumbing Code, §608.3.
Figure 4-31: Backflow Prevention
Newly constructed buildings constructed by the State of California shall have water heating systems designed to derive at least 60 percent of the energy needed for service water heating from site solar energy or recovered energy. There is an exception for buildings where site solar or recovered energy service water heating is economically or physical infeasible, as determined by the state architect. See the Compliance Options section below for more information about solar water heating systems.
All newly installed instantaneous water heaters with an input greater than 6.8 kBtu/h or 2 kW shall have isolation valves on both the incoming cold water supply and the hot water pipe leaving the water heater, to assist in the flushing of the heat exchanger and help prolong the life the water heaters. Instantaneous water heaters with integrated drain ports for servicing are acceptable to meet the requirement and will not require additional isolation valves.
All requirements of §120.3 also apply to service water heating in nonresidential, hotel and motel buildings. See Section 4.5.1.1 for full details
For pipes with conductivity ranges within those specified in Table 4-23, the nominal pipe diameters grouping ranges have changed, as well as the thickness of insulation required for each pipe diameter range. The table is repeated below for ease of reference:
Table 4-23: Pipe Insulation
Source: California Energy Commission, Building Energy Efficiency Standards, Table 120.3-A
In addition to the mandatory requirements listed above, there are mandatory requirements that will apply to water heating systems for hotels, motels, and multifamily buildings only. All of these requirements are tied to the mandatory requirements in §160.4 for multifamily occupancies. The applicability of the mandatory features listed above will change depending on whether the water heating system has a central system or uses individual water heaters.
Systems using gas or propane water heaters to serve individual dwelling units must include:
1. An unobstructed, dedicated 125V 20A receptacle connected to the electrical panel via a 120/240V 3-conductor 10-gauge copper branch circuit, which is no further than 3 ft. from the water heater. The unused conductor ends must be electrically isolated and labeled “spare”, and a single-pole breaker space must be reserved next to the breaker for the branch circuit
2. Either a Category III/IV vent, or a Type B vent with straight pipe between the outside end and the water heater location. Higher output water heaters often require different vent materials due to the presence of acidic condensation from flue gases. The standard Type B vent installed for conventional atmospheric gas water heaters is made of steel and would soon be destroyed by the condensate. Thus, the Energy Code only allows Type B vents for water heaters when there is a straight shot between the water heater and where the vent leaves the building, with no bends along the path of the Type B vent, except the portion of the vent outside the building, and in the space where the water heater is installed. The installation shall meet all code and manufacturers’ guidelines. Because Category III and IV pipes are usually smaller than those for Type B vents, a straight Type B vent can be easily modified into a Category III or IV vent by simply inserting a new vent pipe through the existing Type B vent pipe. A flue pipe that makes bends though the building structure is not easy to retrofit, and, thus, these flues must be either Category III or IV vent pipes. Only stainless steel Category III and IV vents are compatible with typical atmospheric combustion storage water heaters
3. A condensate drain placed near the water heater, no higher than the base of the tank, which allows the condensate removal without relying on a sump pump.
4. A gas line designed to provide 200,000 Btu/h gas supply capacity to the water heater, to accommodate future retrofit to a gas instantaneous water heater, which usually has a heat input capacity of 199,000 Btu/h or higher. Installing a larger gas line during construction is less expensive than a future gas line retrofit. Gas pipe sizing for the building needs to consider piping layout and gas supply requirements for other gas appliances (e.g., clothes dryers, furnaces, ranges and ovens, fireplace burners). The minimum gas pipe size for water heaters is ¾-inch. The exact gas piping system should be designed following the California Plumbing Code.
Solar water-heating systems and collectors shall be certified and rated by the Solar Rating and Certification Corporation (SRCC), the International Association of Plumbing and Mechanical Officials, Research and Testing (IAPMO R&T), or by a listing agency that is approved by the Executive Director.
Please see Section 4.2.9 for full details.
160.4(f)|topic=(f) Insulation for Piping and TanksMultifamily and hotel/motel domestic hot water system piping must be insulated per Table [160.4-A], or Table [120.3-A] for applications above 140F. The Energy Code also requires that pipe insulation be protected from damage by moisture, UV and physical abrasion including but not limited to the following:
•Insulation exposed to weather shall be installed with a cover suitable for outdoor service. The cover shall be water retardant and provides shielding from solar radiation that can cause degradation of the material. Insulation must be protected by an external covering unless the insulation has been approved for exterior use using a recognized federal test procedure. Adhesive tape shall not be used as protection for insulation exposed to weather.
•Insulation covering chilled water piping and refrigerant suction piping located outside the conditioned space shall have a Class I or Class II vapor retarder. All penetrations and joints of which shall be sealed.
•Pipe insulation buried below grade must have a waterproof, uncrushable casing or sleeve. The Energy Code does not define uncrushability, as any material can be crushed, given enough pressure, and thus it is left to the professional judgement of the designer The internal cross-section or diameter of the casing or sleeve shall be large enough to allow for insulation of the hot water piping. Pre-insulated pipe with an integrated protection sleeve will also meet this requirement.
There are exceptions to the requirements for pipe insulation, as described below:
•Pipes completely surrounded with at least four inches of attic insulation,2 inches of crawlspace insulation, or 1 inch of wall insulation; any section of pipe not meeting this criterion must be insulated.
•Piping in walls meeting Quality Insulation Installation (QII) requirements as specified in the Reference Residential Appendix RA3.5. Otherwise, the section of pipe not meeting the QII specifications must be insulated.
•Factory-installed piping within space-conditioning equipment certified under 110.1 or 110.2|topic=SECTION 110.2 – MANDATORY REQUIREMENTS FOR SPACE-CONDITIONING EQUIPMENT.
•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.
§140.5 (a)&(c)
Service water heating for school buildings less than 25,000 ft2 and less than 4 stories in climate zones 2-15 must use a heat pump water heater that meets all mandatory requirements of Sections 110.1, 110.3, and 120.3. However, bathrooms in these buildings that are served by individual water heaters may use electric instantaneous water heaters.
All other nonresidential occupancies can use a wider range of acceptable water heater types, as long as the water heater meets the mandatory requirements under Sections 110.1, 110.3, and 120.3, and the high-capacity service water heating system requirements under Section 140.5(c).
Gas service water-heating systems with a total installed input capacity of 1 MMBtu/h (1 million Btu/h) or greater must have service water-heating equipment with a thermal efficiency of 90 percent or higher. Multiple units can meet this requirement if the water-heating input provided by equipment with thermal efficiencies above and below 90 percent averages out to an input capacity-weighted average of at least 90 percent. It should be noted that individual gas water heaters of 100,000 Btu/h or less are not counted in calculating total system input or efficiency. There are 2 main exceptions from this requirement:
1. Systems that derive 25 percent of their annual water heating energy from site-solar or site-recovered sources
2. Water heaters installed in individual dwelling units
Example: WH sys has 110k @ 85%, 2x 300k @ 90%, 400k @ 95%, 90k @ 70% - wt. avg. = ~91%, because ≤ 100k is excluded, so such a system would be acceptable.
For water heating systems for multifamily and hotel/motel buildings, the code references to the multifamily prescriptive requirements under Section 170.2. The executive director can also approve another water heating system that uses no more energy than one described in Sections 4.8.4.1 or 4.8.4.2 below. The following paragraphs recap these requirements.
Systems for individual dwelling units with recirculation distribution systems must use Demand Recirculation with a manual on/off control meeting RA4.4.9.
There are 3 options for water heating systems serving single dwelling units:
1. One 240V heat pump water heater (HPWH); a compact hot water distribution system (CHWDS) meeting RA4.4.6 is also required in climate zones s 1 & 16. A drain water heat recovery (DWHR) device meeting RA3.6.9 is also required in climate zone 16
2. One HPWH meeting NEEA Tier 3 or higher specifications. A DWHR device meeting RA3.6.9 is also required in climate zone 16
3. A gas or propane tankless water heater of 200 kBtu/h or less
§170.2(d)2&3
Systems serving multiple dwelling units must be central water heating systems with recirculation distribution systems meeting §110.3(c)2&5 (please see Sections 4.8.1.3 and 4.8.1.6 for details), able to automatically control the pump based on hot water demand and water return temperature. Water heating systems serving buildings with 8 or fewer dwelling units do not require recirculation systems.
There are 2 water heating system options:
1. HPWH with the following:
i. Recirculation loop return connected to a recirculation loop tank
ii. If auxiliary heating is needed, the recirculation loop tank heater must be electric and capable of multi-pass operation
iii. If the HPWH is single-pass, the main thermal tanks must be piped in series. If multi-pass, the main thermal tanks must be piped in parallel
iv. Main tank must be set to 135°F
v. Recirculation loop tank temperature must be 10°F lower than that of the main tank; the recirculation loop tank water must be used to maintain the temperature before using recirculation loop tank heater
vi. The compressor must shut off when the ambient temperature is 40°F or below.
2. A gas or propane central water heater meeting the following:
i. In climate zones 1-9, if the input is 1MM Btu/h or greater, then any water heating equipment must have a thermal efficiency of 90% or greater. Multiple units can be used if their input capacity-weighted average of 90% or more. Water heaters of 100k Btu/h or less are not included in this calculation. There is an Exception for systems deriving 25% or more of their annual energy from site-solar or site-recovered energy.
ii. Solar water heating (described below)
Solar water heating is prescriptively required for gas or propane water heating systems serving multiple dwelling units in a motel/hotel or multifamily building. The minimum solar savings fraction (SSF) is dependent on the climate zone: 0.20 for CZ 1 through 9, and 0.35 for CZ 10 through 16. A provision allows a reduced SSF, if drain water heat recovery devices are installed. The Energy Code do 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 high-rise multifamily and hotel/motel buildings from needing to set aside a solar zone for future solar PV installation (Exception 2 to §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 the solar collectors and the 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. This is especially critical for multifamily-sized systems, due to load variability.
To be conservative, the highest SSF requirement called for by the 2022 Energy Code is 35 percent. Industry standard sizing for an active system is generally 1.5 sq ft collector area per gallon capacity for solar tanks. For more detailed guidance and best practices, there are many publicly available industry design guidelines. Two such resources developed by or 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 recommend 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 the solar tank. The design should minimize the length of plumbing, and thus reduce pipe surface areas susceptible to heat loss as well as the quantity of piping materials needed for the installation. The distance between collectors and the solar tank should also be as short as practically possible.
A dual-loop design is illustrated in Figure 4-32. 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, refer to the Universal Plumbing Code.
Figure 4-32: Example of a Dual-Loop Recirculation System
Figure 4-32 provides an example of how to implement dual-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 the top floor with each recirculation loop serving exactly half of the building. The recirculation loops are located in the middle floor to minimize branch pipe length to each of the dwelling units. Figure 4-32 also illustrates how the solar water heating system and demand control are integrated.
For buildings with complicated layouts, an optimum design for recirculation loops depends on the building geometry. In general, the system should be designed to have each loop serving an 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 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. In all cases, a simplified routing of recirculation loops should be used to keep recirculation pipes as short as possible Figure 4-33 shows examples of dual-loop recirculation system designs in buildings that have complicated floor plans.
Figure 4-33: Examples of Dual-Loop Recirculation System Designs in Buildings That Have Complicated Floor Plans
Location of water heating equipment in the building should be carefully considered to properly implement the dual-loop design. The goal is to keep overall pipe length as short as possible. For example, for buildings that do not have complicated floor plans; the designer should consider locating the water heating equipment at the center of the building footprint rather than at one end of the building which helps to minimize the pipe length needed. If a water heating system serves several distinct building sections, the water heating equipment would preferably nest in between these sections.
With the prescriptive solar water heating requirement in the Energy Code, it is especially important to consider the integration between the hot water recirculation system and the solar water heating system. Based on feedback from industry stakeholders, most solar water heating systems are only configured to operate as a pre-heater for 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 floor plan and are relatively independent of the solar water heating system. The system’s gas water heating equipment and solar tank should be located close together to avoid heat loss from the piping that connects 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. Minimizing pipe length helps to reduce domestic hot water (DHW) system energy use as well as system plumbing cost.
The prescriptive requirement for DHW systems serving multiple dwelling units requires the installation of a demand recirculation control to minimize pump operation, based on hot water demand and recirculation return temperatures, instead of the manual demand controls used in single dwelling units. The temperature sensor should be installed at the last branch pipe along the recirculation loop to measure the hot water return temperature most accurately.
Any system that does not meet the prescriptive requirements must instead meet the standard design building energy budget or otherwise follow the performance compliance approach.
Pool and spa heating systems must be certified by the manufacturer and listed by the Energy Commission as having:
1. For equipment subject to state or federal appliance efficiency regulations, a listing in MAEDbS, showing compliance
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
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.
No electric resistance heating, except:
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.
b) Pools or spas deriving at least 60 percent of the annual heating energy from site solar energy or recovered energy.
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 one of three 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, (example: a built-in connection could be a capped off tee fitting between the filter and heater)
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.
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.
Pool and spa systems available to multiple tenants or to the public must comply with the applicable requirements of §110.4, detailed above.
Pool and spa systems installed for exclusive use by a single tenant shall comply with the applicable requirements of §150.0(p).