What efficiency and hot‑water distribution return temperature limits apply to high‑capacity boilers?

Grounded in the retrieved California Energy Code — click a citation to read the verbatim passage:

• § 140.4 High relevance — show source text

  2025 CALIFORNIA ENERGY CODE 125

  on Jul 18, 2025 11:14 AM (CDT) THEREUNDER.

  NONRESIDENTIAL AND HOTEL/MOTEL OCCUPANCIES—PERFORMANCE AND PRESCRIPTIVE

  COMPLIANCE APPROACHES FOR ACHIEVING ENERGY EFFICIENCY

  7. Hydronic heat pump (WLHP) controls. Hydronic heat pumps connected to a common heat pump water loop with central devices for heat rejection and heat addition shall have controls that are capable of providing a heat pump water supply temperature dead band of at least 20°F between initiation of heat rejection and heat addition by the central devices.

  Exception to Section 140.4(k)7: Where a system loop temperature optimization controller is used to determine the most efficient operating temperature based on real-time conditions of demand and capacity, dead bands of less than 20°F shall be allowed. 8. High capacity space heating gas boiler systems. In Climate Zones 1 through 6, 9 through 14, and 16, gas hot water boiler systems for space heating with a total system input of at least 1 MMBtu/h but no more than 10 MMBtu/h shall meet all of the following requirements. A. Boiler system efficiency. Gas hot water boilers shall have a minimum thermal efficiency of 90 percent. Systems with multiple boilers can meet this requirement if the space-heating input provided by equipment with thermal efficiencies above and below 90 percent has an input capacity-weighted average thermal efficiency of at least 90 percent. For boilers federally regulated by combustion efficiency, the calculation for the input capacity-weighted average thermal efficiency shall use the combustion efficiency value. B. Hot water distribution design. The hot water distribution system shall be designed to comply with Items i and ii. i. Coils and other heat exchangers shall be selected so that at design conditions the hot water return temperature entering the boilers is 120°F or less. ii. Under all operating conditions, the water temperature entering the boiler is 120°F or less or the flow rate of supply hot water that recirculates directly into the return system, such as by three-way valves or minimum flow bypass controls, shall be no greater than 20 percent of the design flow of the operating boilers. Exception 1 to Section 140.4(k)8: Where 25 percent of the annual space heating requirement is provided by on-site renewable energy, site-recovered energy or heat recovery chillers. Exception 2 to Section 140.4(k)8: Space heating boilers installed in individual dwelling units. Exception 3 to Section 140.4(k)8: Where 50 percent or more of the design heating load is served using perimeter convective heating, radiant ceiling panels or both. Exception 4 to Section 140.4(k)8: Individual gas boilers with input capacity less than 300,000 Btu/h shall not be included in the calculations of the total system input or total system efficiency.

  (l) Reserved.

  (m) Fan control. Each cooling system listed in Table 140.4-I shall be designed to vary the indoor fan airflow as a function of load and shall comply with the following requirements:

  1. DX and chilled water cooling systems that control the capacity of the mechanical cooling directly based on occupied space temperature shall A. Have a minimum of two stages of fan control with no more than 66 percent speed when operating on stage 1; and B. Draw no more than 40 percent of the fan power at full fan speed, when operating at 66 percent speed.
• § 140.4 High relevance — show source text

  i. Coils and other heat exchangers shall be selected so that at design conditions the hot water return temperature entering the boilers is 120°F or less. ii. Under all operating conditions, the water temperature entering the boiler is 120°F or less or the flow rate of supply hot water that recirculates directly into the return system, such as by three-way valves or minimum flow bypass controls, shall be no greater than 20 percent of the design flow of the operating boilers. Exception 1 to Section 140.4(k)8: Where 25 percent of the annual space heating requirement is provided by on-site renewable energy, site-recovered energy or heat recovery chillers. Exception 2 to Section 140.4(k)8: Space heating boilers installed in individual dwelling units. Exception 3 to Section 140.4(k)8: Where 50 percent or more of the design heating load is served using perimeter convective heating, radiant ceiling panels or both. Exception 4 to Section 140.4(k)8: Individual gas boilers with input capacity less than 300,000 Btu/h shall not be included in the calculations of the total system input or total system efficiency.

  (l) Reserved.

  (m) Fan control. Each cooling system listed in Table 140.4-I shall be designed to vary the indoor fan airflow as a function of load and shall comply with the following requirements:

  1. DX and chilled water cooling systems that control the capacity of the mechanical cooling directly based on occupied space temperature shall A. Have a minimum of two stages of fan control with no more than 66 percent speed when operating on stage 1; and B. Draw no more than 40 percent of the fan power at full fan speed, when operating at 66 percent speed.
  2. All other systems, including but not limited to DX cooling systems and chilled water systems that control the space temperature by modulating the airflow to the space, shall have proportional fan control such that at 50 percent air flow the power draw is no more than 30 percent of the fan power at full fan speed.
  3. Systems that include an air side economizer to meet Section 140.4(e)1 shall have a minimum of two speeds of fan control during economizer operation.

  Exception 1 to Section 140.4(m): Modulating fan control is not required for chilled water systems with all fan motors < 1 HP, or for evaporative systems with all fan motors < 1 HP, if the systems are not used to provide ventilation air and all indoor fans cycle with the load.

  Exception 2 to Section 140.4(m): Systems serving healthcare facilities.

  TABLE 140.4-I—FAN CONTROL SYSTEMS	Col2	Col3
  COOLING SYSTEM TYPE	FAN MOTOR SIZE	COOLING CAPACITY
  DX cooling	Any	≥ 65,000 Btu/hr
  Chilled water and evaporative	≥ 1/4 HP	Any

  (n) Mechanical system shut-off. Any directly conditioned space with operable wall or roof openings to the outdoors shall be provided with interlock controls that disable or reset the temperature setpoint to 55°F for mechanical heating and disable or reset the temperature setpoint to 90°F for mechanical cooling to that space when any such opening is open for more than 5 minutes.

  Exception 1 to Section 140.4(n): Interlocks are not required on doors with automatic closing devices.

• § 503.4 High relevance — show source text

  See reference document for detailed information. 3 Et = thermal efficiency. See reference document for detailed information. 4 Maximum capacity—minimum and maximum ratings as provided for and allowed by the unit’s controls. 5 Includes oil-fired (residual). 6 Boilers shall not be equipped with a constant burning pilot light. 7 A boiler not equipped with a tankless domestic water-heating coil shall be equipped with an automatic means for adjusting the temperature of the water such that an incremental change in inferred heat load produces a corresponding incremental change in the temperature of the water supplied. 8 For new construction, refer to Section E 503.4 for additional system compliance requirements. 9 See Informative Appendix F, Table F-4 of ASHRAE 90.1, for U.S. minimum efficiencies for residential products covered by USDOE requirements for U.S. applications.

  458 2025 CALIFORNIA MECHANICAL CODE

  ), Copyright © 2025 IAPMO, and may not be used for any other purpose or distributed to any other persons or parties.

  APPENDIX E

  TABLE E 503.7.1(7) PERFORMANCE REQUIREMENTS FOR HEAT REJECTION EQUIPMENT—MINIMUM EFFICIENCY REQUIREMENTS

  [ASHRAE 90.1: TABLE 6.8.1-7]

  EQUIPMENT TYPE	TOTAL SYSTEM HEAT- REJECTION CAPACITY AT RATED CONDITIONS	SUBCATEGORY OR RATING CONDITION8	PERFORMANCE REQUIRED1,2,3,6,7	TEST PROCEDURE4,5
  Propeller or axial fan open- circuit cooling towers	All	95°F entering water 85°F leaving water 75°F entering wb	≥40.2 gpm/hp	CTI ATC-105 and CTI STD-201 RS
  Centrifugal fan open-circuit cooling towers	All	95°F entering water 85°F leaving water 75°F entering wb	≥20.0 gpm/hp	CTI ATC-105 and CTI STD-201 RS
  Propeller or axial fan closed- circuit cooling towers	All	102°F entering water 90°F leaving water 75°F entering wb	≥16.1 gpm/hp	CTI ATC-105S and CTI STD-201 RS
  Centrifugal closed- circuit cooling towers	All	102°F entering water 90°F leaving water 75°F entering wb	≥7.0 gpm/hp	CTI ATC-105S and CTI STD-201 RS
  Propeller or axial fan dry coolers (air-cooled fluid cool- ers)	All	115°F entering water 105°F leaving water 95°F entering wb	≥4.5 gpm/hp	CTI ATC-105DS
  Propeller or axial fan evapo- rative condensers	All	R-448A test fluid 165°F entering gas temperature 105°F condensing temperature 75°F entering wb	≥160 000 Btu/h·hp	CTI ATC-106
  Propeller or axial fan evapo- rative condensers	All	Ammonia test fluid 140°F entering gas temperature 96.

• § 503.5.7.3.1 High relevance — show source text

  E 503.5.7.3.1 Boiler Isolation. Where a boiler plant includes more than one boiler, provisions shall be made so that the flow through the boiler is automatically shut off where the boiler is shut down. Where constant-speed hot-water pumps are used to serve multiple boilers, the number of pumps shall be not less than the number of boilers and staged on and off with the boilers.

  [ASHRAE 90.1:6.5.4.3.2]

  E 503.5.7.4 Chilled- and Hot-Water Tempera- ture Reset Controls. Chilled- and hot-water systems with a design capacity exceeding 300 000 Btu/h (88 kW) supplying chilled or heated water to comfort conditioning systems shall include controls that automatically reset supply water temperatures by representative building loads (including return water temperature) or by outdoor air temperature. Where DDC is used to control valves, the set point shall be reset based on valve positions until one valve is nearly wide open or setpoint limits of the system equipment or application have been reached.

  Exceptions:

  (1) Where chilled-water supply is already cold, such as chilled water supplied from a district cooling or thermal energy storage system, such that blending would be required to achieve the reset chilled-water supply temperature.

  (2) Where a specific temperature is required for a process application.

  «

  «

  «

  «

  440 2025 CALIFORNIA MECHANICAL CODE

  ), Copyright © 2025 IAPMO, and may not be used for any other purpose or distributed to any other persons or parties.

  APPENDIX E

  (2) Piping systems that have equivalent or lower total pressure drop than the same system constructed with standard weight steel pipe with piping and fittings sized in accordance with Table E 503.5.7.6. [ASHRAE 90.1:6.5.4.6]

  E 503.5.7.7 Chilled-Water Coil Selection.

  Chilled-water cooling coils shall be selected to provide a 15°F (8°C) or higher temperature difference between leaving and entering water temperatures and a minimum of 57°F (14°C) leaving water temperature at design conditions.

  Exceptions:

  (1) Chilled-water cooling coils that have an air-side pressure drop exceeding 0.70 inch of water (0.17 kPa) when rated at 500 feet per minute (2.54 m/s) face velocity and dry conditions (no condensation).

  (2) Individual fan-cooling units with a design supply airflow rate 5000 cubic feet per minute (ft [3] /min) (2.36 m [3] /s) and less.

  (3) Constant-air-volume systems.

  (4) Coils selected at the maximum temperature difference allowed by the chiller.

  (5) Passive coils (no mechanically supplied airflow).

  (6) Coils with design entering chilled-water temperatures of 50°F (10°C) and higher.

  (7) Coils with design entering air dry-bulb temperatures of 65°F (18°C) and lower. [ASHRAE 90.1:6.5.4.7]

  E 503.5.8 Heat Rejection Equipment. Section E 503.5.8 through Section E 503.5.9 applies to heat-rejection equipment used in comfort cooling systems, such as air-cooled condensers, dry coolers, open-circuit cooling towers, closed-circuit cooling towers, and evaporative condensers.

  »

• § 150.0 High relevance — show source text

  150.0(m)8, Table 160.2-D, 160.3(b)5H, Table 160.6-B, 160.7(a), 170.2(e)2C, 6A Embedded Fan 120.10(a) Emergency Backup 140.4(g), 170.2(c)4E Emittance 10-113, 110.8(i), 110.8(j), 140.3(a)1A, 141.0(b)2B, 150.1(c)11, 150.2(b)1I, 170.2(a)1A, 180.2(b)1A Enclosed Kitchen 150.0(o), Table 150.0-E, 160.2(b)2A Enclosed Parking Garage 120.6(c), 160.2(d) Enclosed Space 140.3(c), 141.0(b)2I, 141.1(c)3, 170.2(b), 180.2(b)4B Enclosure Leakage 150.0(o)1C, 150.1(b)3B, 160.3(d)2, 170.1(d)2H Energy Budget 10-104(b), 140.0(c), 140.1(a), 140.1(b), 140.1(c), 141.0(b)3, 150.1(b)1, 150.1(b)2, 150.1(b)3, 150.2(a)2A, 150.2(b)2, 170.1(a), 170.1(b), 170.1(c), 170.1(d), 180.1(b)1, 180.2(c) Commission 110.0(b), 110.1(b), 110.1(c), 110.2(e), 110.2(f), 110.6(a), 120.2(i), 120.6(e)1, 140.0(c), 140.1(b), 140.1(c), 140.3(a)6E, 140.3(a)9, 140.3(c), 140.4(b)1, 140.4(e)2, 150.0(o)1G, 150.1(a), 150.1(b), 150.1(b)1, 150.1(c)10, 160.2(b)2A, 160.3(a)2H, 170.1(b), 170.2(a)3B, 170.2(c)3B, 170.2(c)4D Commission directory 150.0(h), 150.0(p) Consumption 141.0(c), 150.1(b), 180.3 Design rating (EDR) 150.1(b)1, 150.1(b)3 Efficiency goals 120.8(b) Efficiency ratio (EER) rating 150.1(b)3 Efficient combination 120.6(e) Features 141.0(a)2, 150.2(a)2B, 180.1(b)2 Management Control System (EMCS) 110.2(c), 110.2(e), 110.12(b), 120.2(a), 120.2(i)6, 120.5(a)17, 130.0(e), 130.4(b)2, 140.9(c)3, 150.0(i), 150.0(k)2, 150.

• § 1.9 Medium relevance — show source text

  9| |7 to 8|R-1.9|R-1.9|R-1.9|

  Notes: 1 Insulation R-values, measured in [°F•h•ft 2 /(Btu•in)] [(m•K)/W], are for the insulation as installed and do not include film resistance. The required minimum thicknesses do not consider water vapor transmission and possible surface condensation. Where portions of the building envelope are used as a plenum enclosure, building envelope insulation shall be as required by the most restrictive condition of Section E 503.4.7.1 or ASHRAE 90.1, depending on whether the plenum is located in the roof, wall, or floor. Insulation resistance measured on a horizontal plane in accordance with ASTM C518 at a mean temperature of 75°F (24°C) at the installed thickness. 2 Includes attics above insulated ceilings, parking garages and crawl spaces. 3 Includes return air plenums, with or without exposed roofs above. 4 Return ducts in this duct location do not require insulation.

  TABLE E 503.7.3(1) MINIMUM PIPE INSULATION THICKNESS FOR HEATING AND HOT WATER SYSTEMS [1, 2, 3, 4, 5]

  (STEAM, STEAM CONDENSATE, HOT WATER HEATING, AND DOMESTIC WATER SYSTEMS)

  [ASHRAE 90.1: TABLE 6.8.3-1]

  FLUID OPERATING TEMPERATURE RANGE (F°) AND USAGE	INSULATION CONDUCTIVITY	Col3	NOMINAL PIPE SIZE OR TUBE SIZE (inches)	Col5	Col6	Col7	Col8
  FLUID OPERATING TEMPERATURE RANGE (F°) AND USAGE	CONDUCTIVITY Btu•inch/(h•ft2•°F)	MEAN RATING TEMPERATURE °F	<1	1 to <11_/_2	11_/_2 to <4	4 to <8	≥8
  FLUID OPERATING TEMPERATURE RANGE (F°) AND USAGE	CONDUCTIVITY Btu•inch/(h•ft2•°F)	MEAN RATING TEMPERATURE °F	INSULATION THICKNESS (inches)	INSULATION THICKNESS (inches)	INSULATION THICKNESS (inches)	INSULATION THICKNESS (inches)	INSULATION THICKNESS (inches)
  >350	0.32 to 0.34	250	4.5	5.0	5.0	5.0	5.0
  251 to 350	0.29 to 0.32	200	3.0	4.0	4.5	4.5	4.5
  201 to 250	0.27 to 0.30	150	2.5	2.5	2.5	3.0	3.0
  141 to 200	0.25 to 0.29	125	1.5	1.5	2.0	2.0	2.0
  105 to 140	0.22 to 0.28	100	1.

• California Energy Code Medium relevance — show source text

  |100 psf|1 hr
  23 min|||7|1, 2|11/3| |F/C-4-RC-9|4″|4″ deep (4370 psi);1/4″ reinforcement bars
  at 6″ pitch with3/4″ cover;1/4″ main rein-
  forcement bars at 4″ pitch perpendicular
  with1/2″ cover; 13′1″ span restrained.|150 psf|2 hrs|||7|1, 3|2| |F/C-4-RC-10|4″|4″ thick (5140 psi) deck;1/4″ reinforce-
  ment bars at 71/2″ pitch with7/8″ cover;3/8″
  main reinforcement bars at 33/4″ pitch
  perpendicular with1/2″ cover; 13′1″ span
  restrained.|140 psf|1 hr
  16 min|||7|1, 5|11/4| |F/C-4-RC-11|4″|4″ thick (4000 psi) concrete deck;
  3″ × 11/2″ × 4 lbs R.S.J.; 2′6″ C.R.S.; flush
  with top surface; 4″ × 6″ x 13 SWG mesh
  reinforcement 1″ from bottom of slab; 6′6″
  span restrained.|150 psf|2 hrs|||7|1, 3|2| |F/C-4-RC-12|4″|4″ deep (2380 psi) concrete deck;
  3″ × 11/2″ × 4 lbs R.S.J.; 2′6″ C.R.S.; flush
  with top surface; 4″ × 6″ x 13 SWG mesh
  reinforcement 1″ from bottom surface;
  6′6″ span restrained.|150 psf|1 hr
  3 min|||7|1, 2|1| |F/C-4-RC-13|41/2″|41/2″ thick (5200 psi) deck;1/4″ reinforce-
  ment bars at 71/4″ pitch with7/8″ cover;3/8″
  main reinforcement bars at 33/4″ pitch
  perpendicular with1/2″ cover; 13′1″ span
  restrained.|140 psf|2 hrs|||7|1, 3|2| |F/C-4-RC-14|41/2″|41/2″ deep (2525 psi) concrete deck;1/4″
  reinforcement bars at 71/2″ pitch with7/8″
  cover;3/8″ main reinforcement bars at
  33/8″ pitch perpendicular with1/2″ cover;
  13′1″ span restrained.|150 psf|42 min|||7|1, 5|2/3| |F/C-4-RC-15|41/2″|41/2″ deep (4830 psi) concrete deck;
  11/2″ × No.

• § 150.0 Medium relevance — show source text

  150.0(c), 150.0(d),
  150.0(e), 150.0(g), 150.0(q)|110.6, 110.7, 110.8, 150(a),
  150.0(b), 150.0(c), 150.0(d),
  150.0(e), 150.0(g), 150.0(q)|110.6, 110.7, 110.8, 150(a),
  150.0(b), 150.0(c), 150.0(d),
  150.0(e), 150.0(g), 150.0(q)| |Single-family|HVAC (conditioned)|110.2, 110.5, 150.0(h), 150.0(i),
  150.0(j), 150.0(m), 150.0(o)|110.2, 110.5, 150.0(h), 150.0(i),
  150.0(j), 150.0(m), 150.0(o)|110.2, 110.5, 150.0(h), 150.0(i),
  150.0(j), 150.0(m), 150.0(o)|110.2, 110.5, 150.0(h), 150.0(i),
  150.0(j), 150.0(m), 150.0(o)| |Single-family|Water Heating|110.3, 150.0(j, n)|110.3, 150.0(j, n)|110.3, 150.0(j, n)|110.3, 150.0(j, n)| |Single-family|Indoor Lighting
  (conditioned, unconditioned
  and parking garages)|110.9, 130.0, 150.0(k)|110.9, 130.0, 150.0(k)|110.9, 130.0, 150.0(k)|110.9, 130.0, 150.0(k)| |Single-family|Outdoor Lighting|110.9, 130.0, 150.0(k)|110.9, 130.0, 150.0(k)|110.9, 130.0, 150.0(k)|110.9, 130.0, 150.0(k)| |Single-family|Pool and Spa Systems|110.4, 150.0(p)|N.A.|N.A.|N.A.| |Single-family|Solar Ready Buildings|110.10|N.A.|N.A.|N.A.| |Single-family|Electric Ready|150.0(s), 150.0(t), 150.0(u),
  150.0(v)|N.A.|N.A.|N.A.| |Single-family|Solar PV Systems|N.A.|150.0(c)14|150.1(a), (b)|N.A.| |Multifamily|General|160.0|170.2|170.1|180.0| |Multifamily|HVAC (conditioned)|110.6, 110.7, 110.8, 160.1|170.1(a)|170.1(a)|170.1(a)| |Multifamily|Ventilation and Indoor Air Quality|160.2|N.A.|N.A.|N.A.| |Multifamily|HVAC (conditioned)|110.2, 110.5, 160.3|170.2(c)|170.2(c)|170.

• § 110.3 Medium relevance — show source text

  1. Outlet temperature controls. On systems that have a total capacity greater than 167,000 Btu/hr, outlets that require higher than service water temperatures as listed in the ASHRAE Handbook, Applications Volume, shall have separate remote heaters, heat exchangers or boosters to supply the outlet with the higher temperature. Exception to Section 110.3(c)1: Systems covered by California Plumbing Code Section 613.0 shall instead follow the requirements of that section.
  2. Controls for hot water distribution systems. Service hot water systems with circulating pumps or with electrical heat trace systems shall be capable of automatically turning off the system. Exception to Section 110.3(c)2: Systems serving healthcare facilities.
  3. Insulation. Unfired service water heater storage tanks and backup tanks for solar water-heating systems shall have: A. External insulation with an installed R -value of at least R-3.5; or

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

  C. The heat loss of the tank surface based on an 80°F water-air temperature difference shall be less than 6.5 Btu per hour per square foot. 4. Water heating recirculation loops serving multiple dwelling units, high-rise residential, hotel/motel, and nonresiden- tial occupancies. A water heating recirculation loop is a type of hot water distribution system that reduces the time needed to deliver hot water to fixtures that are distant from the water heater, boiler or other water heating equipment. The recirculation loop is comprised of a supply portion, connected to branches that serve multiple dwelling units, guest rooms, or fixtures and a return portion that completes the loop back to the water heating equipment. A water heating recirculation loop shall meet the following requirements: A. Air release valve or vertical pump installation. An automatic air release valve shall be installed on the recirculation loop piping on the inlet side of the recirculation pump and no more than 4 feet from the pump. This valve shall be mounted on top of a vertical riser at least 12 inches in length and shall be accessible for replacement and repair. Alternatively, the pump shall be installed on a vertical section of the return line. B. Recirculation loop backflow prevention. A check valve or similar device shall be located between the recirculation pump and the water heating equipment to prevent water from flowing backwards though the recirculation loop. C. Equipment for pump priming. A hose bibb shall be installed between the pump and the water heating equipment. An isolation valve shall be installed between the hose bibb and the water heating equipment. This hose bibb is used for bleeding air out of the pump after pump replacement. D. Pump isolation valves. 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. E. Cold water supply and recirculation loop connection to hot water storage tank. Storage water heaters and boilers shall be plumbed in accordance with the manufacturer’s specifications The cold water piping and the recirculation loop piping shall not be connected to the hot water storage tank drain port. F. Cold water supply backflow prevention. A check valve shall be installed on the cold water supply line between the hot water system and the next closest tee on the cold water supply line.

• § 87.9 Medium relevance — show source text

  9 kW) and larger| |Additions or
  Alterations|Zone terminal unit such as VAV box|Where existing zones served by the same air handling,
  chilled water, or hot water systems that have DDC| |Additions or
  Alterations|Air handling system or fan coil|Where existing air handling system(s) and fan coil(s)
  served by the same chilled or hot water plant have DDC| |Additions or
  Alterations|New air handling system and all
  new zones served by the system|Individual systems with design heating or cooling capacity of
  300 kBtu/h and larger and supplying more than three zones and
  more than 75 percent of zones are new| |Additions or
  Alterations|New or upgraded chilled water plant|Where all chillers are new and plant design cooling
  capacity is 300 kBtu/h (87.9 kW) and larger| |Additions or
  Alterations|New or upgraded hot water plant|Where all boilers are new and plant design heating
  capacity is 300 kBtu/h (87.9 kW) and larger|

  (k) Optimum start/stop controls. Space conditioning systems with DDC to the zone level shall have optimum start/stop controls. The control algorithm shall, as a minimum, be a function of the difference between space temperature and occupied setpoint, the outdoor air temperature, and the amount of time prior to scheduled occupancy. Mass radiant floor slab systems shall incorporate floor temperature onto the optimum start algorithm.

  Exception to Section 120.2(k): Systems that must operate continuously.

  (l) HVAC hot water temperature. Zones that use hot water for space heating shall be designed for a hot water supply temperature of no greater than 130°F.

  Note: Authority: Sections 25213, 25218, 25218.5, 25402 and 25402.1, Public Resources Code. Reference: Sections 25007, 25008, 25218.5, 25310, 25402, 25402.1, 25402.4, 25402.8, and 25943, Public Resources Code.

  SECTION 120.3—REQUIREMENTS FOR PIPE INSULATION

  Nonresidential and hotel/motel buildings shall comply with the applicable requirements of Sections 120.3(a) through 120.3(c).

  (a) General requirements. The piping conditions listed below for space-conditioning, service water-heating, and process heating and process cooling systems piping with fluid normal operating temperatures listed in Table 120.3-A-1 or Table 120.3-A2, and the fluid distribution system, shall have at least the amount of insulation specified in Subsection (c):

  1. Space cooling systems. All refrigerant suction, chilled water, and brine fluid distribution systems.
  2. Space heating systems. All refrigerant suction, steam, steam condensate and hot water fluid distribution systems.
  3. Service water-heating systems. A. Recirculating system piping, including the supply and return piping to the water heater. B. The first 8 feet of hot and cold outlet piping, including piping between a storage tank and a heat trap, for a nonrecirculating storage system.

  2025 CALIFORNIA ENERGY CODE 75

  on Jul 18, 2025 11:14 AM (CDT) THEREUNDER.

  NONRESIDENTIAL, HOTEL/MOTEL OCCUPANCIES, AND COVERED PROCESSES—MANDATORY REQUIREMENTS

• § 1.859 Medium relevance — show source text

  78|–|1.859|0.463| |35.31|–|2.247|0.559| |38.84|–|2.667|0.663| |42.37|–|3.121|0.775| |45.90|–|3.607|0.895| |49.43|–|4.125|1.022| |52.97|–|–|1.157| |56.50|–|–|1.299| |60.03|–|–|1.449| |63.56|–|–|1.607| |67.09|–|–|1.772| |70.62|–|–|1.944| |81.21|–|–|2.503| |91.81|–|–|3.127| |102.40|–|–|3.813|

  For SI units: 1 standard cubic foot per minute = 28.32 SLPM, 1 inch = 25 mm, 1 foot = 304.8 mm, 1 pound-force per square inch = 6.8947 kPa

  Notes: 1 Based on pressure of 14.7 psig (101 kPa) at 68°F (20°C). 2 Based on pressure of 55 psig (379 kPa) at 68°F (20 °C).

  2025 CALIFORNIA PLUMBING CODE 291

  ), Copyright © 2025 IAPMO, and may not be used for any other purpose or distributed to any other persons or parties.

  HEALTH CARE FACILITIES AND MEDICAL GAS AND MEDICAL VACUUM SYSTEMS

  TABLE 1323.1.4(5) PRESSURE LOSS FOR VACUUM (continued)

  FLOW RATE (SCFM)1	VACUUM LOSS (inch of mercury) PER 100 FEET FOR COPPER TUBE2	Col3	Col4	Col5	Col6
  FLOW RATE (SCFM)1	3⁄4 INCH TUBE	1 INCH TUBE	11⁄4 INCH TUBE	11⁄2 INCH TUBE	2 INCH TUBE
  49.43	–	–	–	3.645	0.956
  52.97	–	–	–	4.122	1.081
  56.50	–	–	–	4.626	1.212
  63.56	–	–	–	–	1.495
  70.62	–	–	–	–	1.803
  77.68	–	–	–	–	2.138
  84.74	–	–	–	–	2.497
  91.81	–	–	–	–	2.882
  98.87	–	–	–	–	3.291
  105.93	–	–	–	–	3.724
  112.99	–	–	–	–	4.181

• § 90.1 Medium relevance — show source text

  [ASHRAE 90.1:7.5.2] L 503.4.3 Large Service Water-Heating Systems. New buildings with service water-heating systems with a total installed input capacity of 1 000 000 Btu/h (293 kW) or greater, provided by high-capacity gas-fired service water-heating equipment shall meet either or both of the following requirements:

  (1) Where a single unit of high-capacity gas-fired service water-heating equipment is installed, it shall have a minimum thermal efficiency ( Et ) of 92 percent. (2) Multiple units of high-capacity gas-fired service water-heating equipment connected to the same service water-heating system shall have a total input-capacity-weighted average thermal efficiency ( Et ) of at least 90 percent, and a minimum of 30 percent of the input of the high-capacity gas-fired service water-heating equipment in the service water heating-system shall have a thermal efficiency ( Et ) of at least 92 percent.

  High-capacity gas-fired service water-heating equipment comprises gas-fired instantaneous water heaters with a rated input both greater than 200 000 Btu/h (58.6 kW) and not less than 4000 British thermal units per hour per gallon [Btu/(h•gal)] (0.3097 kW/L) of stored water, and gas-fired storage water heaters with a rated input both greater than 105 000 Btu/h (30.8 kW) and less than 4000 British thermal units per hour per gallon [Btu/(h•gal)] (0.3097 kW/L) of stored water.

  Exceptions:

  (1) Water heaters installed in individual dwelling units.

  (2) Individual gas water heaters with input capacity not greater than 100 000 Btu/h (29.3 kW). [ASHRAE 90.1:7.5.3] L 503.4.4 Heat Recovery for Service Water Heating. Condenser heat recovery systems shall be installed for heating or preheating of service hot water provided all of the following are true:

  (1) The facility operates 24 hours a day.

  (2) The total installed heat rejection capacity of the water-cooled systems exceeds 6 000 000 Btu/h (1758 kW) of heat rejection.

  (3) The design service water-heating load exceeds 1 000 000 Btu/h (293 kW). [ASHRAE 90.1:6.5.6.2.1]

  512 2025 CALIFORNIA PLUMBING CODE

  ), Copyright © 2025 IAPMO, and may not be used for any other purpose or distributed to any other persons or parties.

  APPENDIX L

  L 503.4.5 Capacity. The required heat recovery system shall have the capacity to provide the smaller of:

  (1) Sixty percent of the peak heat-rejection load at design conditions or

  (2) Preheat of the peak service hot-water draw to 85°F (29°C).

  Exceptions:

  (1) Facilities that employ condenser heat recovery for space heating with a heat recovery design exceeding 30 percent of the peak water-cooled condenser load at design conditions.

• § 170.1 Medium relevance — show source text

  2. Central systems. For systems serving multiple dwelling units, the water-heating system shall meet the applicable requirement of A through F, or shall meet the performance compliance requirements of Section 170.1: A. For heat pump water-heating systems serving multiple dwelling units, the water-heating system shall be installed according to the manufacturer’s design and installation guidelines and meet the following requirements, or meet the requirements of NEEA Advanced Water Heater Specification for commercial heat pump water heater Tier 2 or higher: i. The primary heat pump water heater shall be a single-pass heat pump water heater. ii. The hot water return from the recirculation loop shall connect to a recirculation loop tank and shall not directly connect to the primary heat pump water heater inlet or the primary thermal storage tanks. iii. The fuel source for the recirculation loop tank shall be electricity. iv. The primary storage tank temperature setpoint shall be at least 135°F. v. The recirculation loop tank temperature setpoint shall be at least 10°F lower than the primary thermal storage tank temperature setpoint. vi. The minimum heat pump water heater compressor cut-off temperature shall be equal to or lower than 40°F ambient air temperature. vii. Design documentation shall be provided in accordance with JA14.4. B. For gas or propane systems serving multiple dwelling units, the water-heating system that includes the following components shall be installed: i. For Climate Zones 1 through 9, gas service water-heating systems with a total installed gas water-heating input capacity of 1 MMBtu/h or greater shall have gas service water-heating equipment with a minimum thermal efficiency of 90 percent. Multiple units are allowed to meet this requirement with an input capacity-weighted average of at least 90 percent. Exception 1 to Section 170.2(d)Bi: Individual gas water heaters with input capacity at or below 100,000 Btu/h shall not be included in the calculations of the total system input or total system efficiency. Exception 2 to Section 170.2(d)Bi: If 25 percent of the annual water-heating requirement is provided by sitesolar energy or site-recovered energy. ii. A solar water-heating system meeting the installation criteria specified in Reference Residential Appendix RA4 and with a minimum solar savings fraction of either a. or b. below: a. A minimum solar savings fraction of 0.20 in Climate Zones 1 through 9 or a minimum solar savings fraction of 0.35 in Climate Zones 10 through 16; or b. A minimum solar savings fraction of 0.15 in Climate Zones 1 through 9 or a minimum solar savings fraction of 0.30 in Climate Zones 10 through 16. In addition, a drain water heat recovery system that is field verified as specified in the Reference Appendix RA3.6.9. C. All hot water piping shall be sized in accordance with the California Plumbing Code Appendix M. D. The central system shall have a recirculation system with a mechanical or digital thermostatic master mixing valve on each distribution supply and return loop, and meet the requirements specified in the Residential Reference Appendix RA4.4.19.

  Exception to Section 170.2(d)2D : Buildings with eight or fewer dwelling units. E. Insulation for hot water pipes and plumbing appurtenances shall be field verified as specified in Residential Reference Appendix RA3.6.3. F. A water-heating system serving multiple dwelling units determined by the Executive Director to use no more energy than the one specified in Subsection A or B above.

  2025 CALIFORNIA ENERGY CODE 257

• § 304.8 Medium relevance — show source text

  For SI units: 1 foot = 304.8 mm, 1 ounce = 29.573 mL, 1 inch = 25 mm

  Notes: 1 PP SDR 11 products are not typically used or rated at 180°F (82.2°C). 2 DN is outside diameter.

  L 503.2.2 Additional Requirements for Service Water Heating. Service water heating systems and equipment shall comply with Section L 503.4.1 through Section L 503.4.3. [ASHRAE 90.1:7.2.2]

  L 503.3 Mandatory Provisions. The mandatory provisions of Section L 503.3.1 through Section L 503.3.7 shall be followed.

  L 503.3.1 Load Calculations. Service water-heating system design loads for the purpose of sizing systems and equipment shall be determined in accordance with manufacturer’s published sizing guidelines or generally accepted engineering standards and handbooks acceptable to the adopting authority (e.g., ASHRAE Handbook – HVAC Applications). [ASHRAE 90.1:7.4.1]

  L 503.3.2 Equipment Efficiency. Water-heating equipment, hot-water supply boilers used solely for heating potable water, pool heaters, and hot water storage tanks shall comply with the criteria listed in Table L 503.3.2. Where multiple criteria are listed, all criteria shall be met. The omission of minimum performance requirements for certain classes of equipment does not preclude the use of such equipment where appropriate. Equipment not listed in Table L 503.3.2 has no minimum performance requirements.

  Exceptions: Water heaters and hot-water supply boilers having more than 140 gallons (530 L) of storage capacity are not required to meet the standby loss (SL) requirements of Table L 503.3.2 where:

  (1) The tank surface is thermally insulated to R-12.5.

  (2) A standing pilot light is not installed.

  (3) Gas- or oil-fired storage water heaters have a flue damper or fan-assisted combustion. [ASHRAE 90.1:7.4.2]

  L 503.3.3 Service Hot Water Piping Insulation. Insulation of hot water and return piping shall meet the provisions in Section L 501.2.

  L 503.3.4 Hot Water System Design. Hot water systems shall comply with the following:

  (1) Circulating hot water systems shall be arranged so that the circulating pump(s) are capable of being turned off (automatically or manually) where the hot water system is not in operation.

  Exception: For healthcare facilities, long term care facilities, hotels, or motels, devices that automatically turn off the circulation pump(s) shall not be required.

  (2) Where used to maintain storage tank water temperature, circulating pump(s) shall be equipped with controls limiting operation to a period from the start of the heating cycle to a maximum of 5 minutes after the end of the heating cycle.

  (3) The maximum volume of water contained in hot water distribution lines between the water heater and the fixture stop or connection to showers, kitchen faucets, and lavatories shall be determined in accordance with Section L 502.7.

  L 503.3.5 Service Water Heating System Con- trols. Service water heating system controls shall comply with Section L 503.3.5(1) and Section L 503.3.5(2).

• § 140.4 Medium relevance — show source text

  Exception 1 to Section 140.4(k)4: Hydronic systems that use variable flow to reduce pumping energy in accordance with 140.4(k)1.

  Exception 2 to Section 140.4(k)4: Systems serving healthcare facilities. 5. Water-cooled air conditioner and hydronic heat pump systems. Water circulation systems serving water-cooled air conditioners, hydronic heat pumps, or both that have total pump system power exceeding 5 hp shall have flow controls that meet the requirements of Section 140.4(k)6. Each such air conditioner or heat pump shall have a two-position automatic valve interlocked to shut off water flow when the compressor is off.

  6. Variable flow controls.

  A. Variable speed drives. Individual pumps serving variable flow systems and having a motor horsepower exceeding 5 hp shall have controls or devices (such as variable speed control) that will result in pump motor demand of no more than 30 percent of design wattage at 50 percent of design water flow. The pumps shall be controlled as a function of required differential pressure. B. Pressure sensor location and setpoint. i. For systems without direct digital control of individual coils reporting to the central control panel, differential pressure shall be measured at the most remote heat exchanger or the heat exchanger requiring the greatest differential pressure. ii. For systems with direct digital control of individual coils with a central control panel, the static pressure setpoint shall be reset based on the valve requiring the most pressure, and the setpoint shall be no less than 80 percent open. Pressure sensors may be mounted anywhere.

  Exception 1 to Section 140.4(k)6: Heating hot water systems.

  Exception 2 to Section 140.4(k)6: Condenser water systems serving only water-cooled chillers.

  2025 CALIFORNIA ENERGY CODE 125

  on Jul 18, 2025 11:14 AM (CDT) THEREUNDER.

  NONRESIDENTIAL AND HOTEL/MOTEL OCCUPANCIES—PERFORMANCE AND PRESCRIPTIVE

  COMPLIANCE APPROACHES FOR ACHIEVING ENERGY EFFICIENCY

  7. Hydronic heat pump (WLHP) controls. Hydronic heat pumps connected to a common heat pump water loop with central devices for heat rejection and heat addition shall have controls that are capable of providing a heat pump water supply temperature dead band of at least 20°F between initiation of heat rejection and heat addition by the central devices.

  Exception to Section 140.4(k)7: Where a system loop temperature optimization controller is used to determine the most efficient operating temperature based on real-time conditions of demand and capacity, dead bands of less than 20°F shall be allowed. 8. High capacity space heating gas boiler systems. In Climate Zones 1 through 6, 9 through 14, and 16, gas hot water boiler systems for space heating with a total system input of at least 1 MMBtu/h but no more than 10 MMBtu/h shall meet all of the following requirements. A. Boiler system efficiency. Gas hot water boilers shall have a minimum thermal efficiency of 90 percent. Systems with multiple boilers can meet this requirement if the space-heating input provided by equipment with thermal efficiencies above and below 90 percent has an input capacity-weighted average thermal efficiency of at least 90 percent. For boilers federally regulated by combustion efficiency, the calculation for the input capacity-weighted average thermal efficiency shall use the combustion efficiency value. B. **Hot water distribution design.

• § 0.27 Medium relevance — show source text

  STEAM CONDENSATE, AND HOT WATER)2, 3**|HEATING SYSTEMS (STEAM, STEAM CONDENSATE, AND HOT WATER)2, 3|HEATING SYSTEMS (STEAM, STEAM CONDENSATE, AND HOT WATER)2, 3|HEATING SYSTEMS (STEAM, STEAM CONDENSATE, AND HOT WATER)2, 3|HEATING SYSTEMS (STEAM, STEAM CONDENSATE, AND HOT WATER)2, 3|HEATING SYSTEMS (STEAM, STEAM CONDENSATE, AND HOT WATER)2, 3|HEATING SYSTEMS (STEAM, STEAM CONDENSATE, AND HOT WATER)2, 3|HEATING SYSTEMS (STEAM, STEAM CONDENSATE, AND HOT WATER)2, 3| |201–250|0.27–0.30|150|1.5|1.5|2.0|2.0|2.0| |141–200|0.25–0.29|125|1.0|1.0|1.0|1.5|1.5| |105–140|0.22–0.28|100|0.5|0.5|1.0|1.0|1.0| |COOLING SYSTEMS (CHILLED WATER, BRINE, AND REFRIGERANT)4|COOLING SYSTEMS (CHILLED WATER, BRINE, AND REFRIGERANT)4|COOLING SYSTEMS (CHILLED WATER, BRINE, AND REFRIGERANT)4|COOLING SYSTEMS (CHILLED WATER, BRINE, AND REFRIGERANT)4|COOLING SYSTEMS (CHILLED WATER, BRINE, AND REFRIGERANT)4|COOLING SYSTEMS (CHILLED WATER, BRINE, AND REFRIGERANT)4|COOLING SYSTEMS (CHILLED WATER, BRINE, AND REFRIGERANT)4|COOLING SYSTEMS (CHILLED WATER, BRINE, AND REFRIGERANT)4| |40–55|0.22–0.28|100|0.5|0.5|1.0|1.0|1.0| |Below 40|0.22–0.28|100|0.5|1.0|1.0|1.0|1.5|

  For SI Units: °C= (°F-32)/1.8, 1 British thermal unit inch per hour square foot degree Fahrenheit = [0.1 W/(m•K)], 1 inch = 25 mm

  Notes: 1 For insulation outside the stated conductivity range, the minimum thickness ( T ) shall be determined as follows: T = r {(1 + t/r) [K/k ] – 1}

  Where:

  T = minimum insulation thickness (inches). r = actual outside radius of pipe (inches) (mm). t = insulation thickness listed in this table for applicable fluid temperature and pipe size. K = conductivity of alternate material at mean rating temperature indicated for the applicable fluid temperature [Btu•in/(h•ft [2] - °F)] [W/(m•K)]. k = the upper value of the conductivity range listed in this table for the applicable fluid temperature. 2 These thicknesses are based on energy efficiency considerations only. Additional insulation is sometimes required relative to safety issues/surface temperature.

• § 90.1 Medium relevance — show source text

  (3) Variable flow is not required for primary pumps in a primary/secondary system.

  (4) Variable flow is not required for a coil pump provided for freeze protection.

  (5) Variable flow is not required for heat recovery coil runaround loops. [ASHRAE 90.1:6.5.4.2]

  CHILLED WATER PUMPS IN THESE CLIMATE ZONES	HEATING WATER PUMPS IN THESE CLIMATE ZONES	MOTOR NAMEPLATE HORSEPOWER
  0A, 0B, 1A, 1B, 2B	NR	≥2 hp
  2A, 3B	NR	≥3 hp
  3A, 3C, 4A, 4B	7, 8	≥5 hp
  4C, 5A, 5B, 5C, 6A, 6B	3C, 5A, 5C, 6A, 6B	≥7.5 hp
  ─	4A, 4C, 5B	≥10 hp
  7, 8	4B	≥15 hp
  ─	2A, 2B, 3A, 3B	≥25 hp
  ─	1B	≥100 hp
  ─	0A, 0B, 1A	≥200 hp

  For SI units: 1 horsepower = 0.746 kW

  E 503.5.7.3 Chiller and Boiler Isolation. Where a chilled-water plant includes more than one chiller, provisions shall be made so that the fluid flow through the chiller is automatically shut off where the chiller is shut down. Chillers piped in series for the purpose of increased temperature differential, shall be considered as one chiller. Where constant-speed chilled-water or condenser water pumps are used to serve multiple chillers, the number of pumps shall be not less than the number of chillers and staged on and off with the chillers. [ASHRAE 90.1:6.5.4.3.1]

  E 503.5.7.3.1 Boiler Isolation. Where a boiler plant includes more than one boiler, provisions shall be made so that the flow through the boiler is automatically shut off where the boiler is shut down. Where constant-speed hot-water pumps are used to serve multiple boilers, the number of pumps shall be not less than the number of boilers and staged on and off with the boilers.

  [ASHRAE 90.1:6.5.4.3.2]

  E 503.5.7.4 Chilled- and Hot-Water Tempera- ture Reset Controls. Chilled- and hot-water systems with a design capacity exceeding 300 000 Btu/h (88 kW) supplying chilled or heated water to comfort conditioning systems shall include controls that automatically reset supply water temperatures by representative building loads (including return water temperature) or by outdoor air temperature. Where DDC is used to control valves, the set point shall be reset based on valve positions until one valve is nearly wide open or setpoint limits of the system equipment or application have been reached.

  Exceptions: