Chapter 17 — GEOTHERMAL ENERGY SYSTEMS AND AMBIENT TEMPERATURE LOOPS

(Matrix Adoption Tables are non-regulatory, intended only as an aid to the code user. See Chapter 1 for state agency authority and building applications.)

This state agency does not adopt sections identified with the following symbol: † The Office of the State Fire Marshal’s adoption of this chapter or individual sections is applicable to structures regulated by other state agencies pursuant to Section 1.11.0.

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

346 2025 CALIFORNIA MECHANICAL CODE

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

»

»»

»

»

»

»

Part I – General.

geothermal energy systems such as, but not limited to, building systems coupled with a ground-heat exchanger, submerged heat exchanger using water-based fluid as a heat transfer medium, or groundwater (well). The regulations of this chapter shall govern the construction, location and installation of geothermal energy systems.

Part I through Part V of this chapter shall apply to geothermal energy systems and district ambient temperature loop systems that circulate ground-ambient-temperature water to be used in end-use buildings as a thermal source or sink via water source heat pump or reversing chiller. The systems shall operate to permit independent and bi-directional heating and cooling for comfort and water heating such as, but not limited to, building systems coupled with ground district ambient temperature loops, a ground-heat exchanger, submerged heat exchanger using water-based fluid as a heat transfer medium, or groundwater (well), or such local resources to the advantage of the district. Central district auxiliary components shall add or reject heat to benefit district ability to reduce both power consumption and demand combined with energy sharing. The regulations of this chapter shall govern the construction, location and installation of ground temperature thermal distribution districts from 100 percent geothermal energy system to multiple hybrid district systems.

1701.1.1 Prior to Construction. Documents for permits shall be submitted prior to the construction of a building system, ground-heat exchanger, submerged heat exchanger, or water well. Permits shall be issued by the Authority Having Jurisdiction.

1701.1.2 Equipment, Accessories, Components, and Materials. The mechanical equipment, accessories, components, and materials used shall be of the type and rating approved for the specific use.

1701.1.3 Indoor Piping. Indoor piping, fittings, and accessories that are part of the groundwater system shall be in accordance with Section 1703.5 and Chapter 12.

uments for the building system portion of the geothermal energy system shall be submitted to the Authority Having Jurisdiction.

to designing the geothermal system. The requirements for construction documents shall be defined by the Authority Having Jurisdiction. Where no guidance is provided, the following information shall be provided:

CHAPTER 17

GEOTHERMAL ENERGY SYSTEMS AND AMBIENT TEMPERATURE LOOPS

(1) Ground-heat exchanger dimensions.

(2) Grout or sealing specifications, as applicable.

(3) Dimensions from building to water well, ground-heat exchanger, or submerged heat exchanger.

(4) Operating temperatures and pressures.

The installation of used pipe, fittings, valves, and other materials shall not be permitted.

heat pump ground-loop piping system shall not be in direct contact with building materials that cause the piping or fitting material to degrade or corrode, or that interferes with the operation of the system.

as to prevent detrimental strains and stresses in the pipe. Provisions shall be made to protect piping from damage resulting from expansion, contraction, and structural settlement. Piping shall be installed so as to avoid structural stresses or strains within building components.

shall be capable of resisting hydrostatic and hydrodynamic loads and stresses, including the effects of buoyancy, during the occurrence of flooding to the design flood elevation.

systems shall be designed so that the flow velocities do not exceed the maximum flow velocity recommended by the pipe and fittings manufacturer. Flow velocities shall be controlled to reduce the possibility of water hammer.

materials used in the system shall be chemically compatible with the pipe, tubing, fittings, and mechanical systems.

be compatible with the makeup fluid supplied to the system.

1701.11.1 Water Quality. The makeup water quality within the closed loop ground source heat pump system shall be in accordance with IAPMO/ANSI H1001.1, ANSI/CSA/IGSHPA C448, or Table 1701.11.1. The quality of potable water shall be in accordance with the Authority Having Jurisdiction.

1701.11.2 Compatibility. System components shall be compatible with system fluids including, but not limited to, antifreeze. For systems utilizing chemical additives, system components and fluids shall be tested and approved for compatibility.

groundwater system shall be protected with an approved

«

«

«

«

«

«

«

«

««

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

GEOTHERMAL ENERGY SYSTEMS AND AMBIENT TEMPERATURE LOOPS

ground source heat pump systems shall be approved for installation with the piping materials to be installed, and shall comply with the standards listed in Table 1703.3. Fittings for use in DX systems shall comply with Section 1715.3.

TABLE 1703.3

GROUND SOURCE LOOP PIPE FITTINGS

als. Underground and submerged piping for a ground-heat exchanger shall be polyethylene (PE) pipe or tubing in accordance with Section 1703.4.1 and Section 1703.4.1.1, or crosslinked polyethylene (PEX) pipe or tubing in accordance with Section 1703.4.2 and Section 1703.4.2.1.

1703.4.1 Polyethylene (PE). Polyethylene pipe or tubing shall be manufactured in accordance with the standards listed in Table 1703.2. Pipe or tubing shall have a minimum wall thickness equal to SDR-11 and shall have a minimum pressure rating of not less than 160 psi (1103 kPa) at 73°F (23°C).

Polyethylene pipe and tubing shall be manufactured from a PE compound that has a pipe material designation code of PE 3608, PE 3708, PE 3710, PE 4608, PE 4708, or PE 4710 as defined in the applicable standards referenced in Table 1703.2, with a cell classification in accordance with ASTM D3350 appropriate for the material designation code, and a color and ultraviolet stabilizer code of C or E. Code E compounds shall be stabilized against deterioration from unprotected exposure to ultraviolet rays for not less than 3 years in accordance with the test criteria specified in ASTM D2513.

1703.4.1.1 Joining Methods for Polyethylene Pipe or Tubing. Joints between high density polyethylene (HDPE) plastic pipe or tubing and fittings shall be installed in accordance with the manufac

TABLE 1701.11.1

WATER QUALITY [1]

WATER QUALITY TABLE 1703.3

GROUND SOURCE LOOP PIPE FITTINGS

Notes: 1 Where chemical additives are used, the acceptable ranges provided shall be in accordance with the equipment manufacturer’s specifications, or this table, whichever is more stringent. 2 The provided acceptable range for chlorides is dependent upon the system heat exchanger and piping materials. See the manufacturer’s specifications for equipment and materials used. 3 The limit provided pertains to makeup water.

«

«

«

«

«

»»

»

»

backflow prevention device. The connection of a discharge line to the sanitary or storm sewer system, or private sewage disposal system, shall be in accordance with the plumbing code or in accordance with the Authority Having Jurisdiction.

TABLE 1701.11.1

WATER QUALITY [1]

Notes: 1 Where chemical additives are used, the acceptable ranges provided shall be in accordance with the equipment manufacturer’s specifications, or this table, whichever is more stringent. 2 The provided acceptable range for chlorides is dependent upon the system heat exchanger and piping materials. See the manufacturer’s specifications for equipment and materials used. 3 The limit provided pertains to makeup water.

The groundheat exchanger design shall be provided by a licensed professional or a designer with the appropriate certifications or credentials as defined by the Authority Having Jurisdiction.

water-based systems, ground source heat pump ground-loop pipe and tubing shall comply with the standards listed in Table 1703.2. Piping and tubing used for DX systems shall be of copper in accordance with Section 1715.3.

TABLE 1703.2

PLASTIC GROUND SOURCE LOOP PIPING

348 2025 CALIFORNIA MECHANICAL CODE

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

GEOTHERMAL ENERGY SYSTEMS AND AMBIENT TEMPERATURE LOOPS

»

»

»

»»

turer’s installation instructions, the appropriate standards listed in accordance with Table 1703.3, and one of the following heat fusion methods:

(1) Butt-fusion joints shall be made in accordance with ASTM F2620.

(2) Socket-fusion joints shall be made in accordance with ASTM F2620.

(3) Electrofusion joints shall be made in accordance with ASTM F1055.

1703.4.2 Polyethylene of Raised Temperature (PE-RT). Polyethylene of raised temperature tubing shall be manufactured in accordance with the standards

listed in Table 1703.2. Tubing shall have a minimum wall thickness equal to SDR 9 and shall have a minimum pressure rating of not less than 160 psi (1103 kPa) at 73°F (23°C).

Polyethylene of raised temperature tubing shall be manufactured from a PE compound that has a pipe material designation code of PE 2708, PE 3608, or PE 4710 as defined in the applicable standards referenced in Table 1703.2, with a cell classification in accordance with ASTM D3350 appropriate for the material designation code.

1703.4.2.1 Joining Methods for Polyethylene of Raised Temperature (PE-RT). Joints between polyethylene of raised temperature (PE-RT) tubing and fittings shall be installed in accordance with the manufacturer’s installation instructions and the

appropriate standards listed in accordance with Table 1703.3.

1703.4.3 Cross-Linked Polyethylene (PEX). Crosslinked polyethylene pipe shall be manufactured in accordance with the standards listed in Table 1703.2. PEX

shall have a minimum tubing material designation code of PEX 1206 and shall have a minimum pressure rating of not less than 160 psi (1103 kPa) at 73°F (23°C).

1703.4.3.1 Joining Methods for Cross- Linked Polyethylene Tubing. Joints between cross-linked polyethylene (PEX) pipe or tubing and fittings shall be installed in accordance with the manufacturer’s installation instructions and the

appropriate standards in accordance with Table 1703.3.

Indoor piping, fittings, and accessories that are part of the groundwater system shall be in accordance with Chapter 12. Such materials shall be rated for the operating temperature and pressures of the system and shall be compatible with the type of transfer medium.

distribution system shall be designed as follows:

(1) Individual heat pumps shall have the capacity to handle the peak load for each zone at its peak hour.

(2) Distribution piping and fittings shall be insulated to prevent condensation inside the building.

(3) An isolation valve shall be installed on both supply and return of each unit.

(4) Condensate drains on heat pumps shall be installed in accordance with the manufacturer’s installation instruc tions.

(5) Air filters shall be installed for heat pump units.

(6) Drain valves shall be installed at the base of each supply and return pipe riser for system flushing.

(7) Piping shall be supported in accordance with Section 313.0 and provisions for vibration, expansion or contraction shall be provided.

(8) Specifications for each heat pump, the heating and cooling capacity, the fluid flow rate, the airflow rate, and the external pressure or head shall be provided on the construction documents.

(9) Manually controlled air vents shall be installed at the high points in the system and drains at the low points. Where the heat-transfer fluid is a salt or alcohol, automatic air vents shall not be installed.

(10)Means for flow balancing for the building loop shall be provided.

(11)Supply and return header temperatures and pressures shall be marked.

sized for the operating conditions and the heat transfer fluid properties.

in ground source-loop piping systems in the locations indicated in Section 1705.2 through Section 1705.8.

on the supply and return side of a heat exchanger.

Exception: Where the heat exchanger is integral with a boiler or is a component of a manufacturer’s boiler and heat exchanger packaged unit, and is capable of being isolated from the hydronic system by the supply and return valves.

on the building supply and return of a central utility system.

on the connection to a pressure vessel.

be installed on both sides of a pressure-reducing valve.

be installed on connections to mechanical equipment and appliances. This requirement does not apply to components of a ground source loop system such as pumps, air separators, metering devices, and similar equipment.

at connections to nondiaphragm-type expansion tanks.

«

««

«

«

«

«

«

«

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

GEOTHERMAL ENERGY SYSTEMS AND AMBIENT TEMPERATURE LOOPS

»

»»

»

»

»

»»

»

be installed on the low-pressure side of a hydronic piping system that has been reduced in pressure. The relief valve shall be set at the maximum pressure of the system design.

Table 1706.1, as applicable. Heat pumps shall also be listed and labeled in accordance with UL 1995 or UL 60335-2-40.

Ground coupled and water source heat pumps shall be listed in accordance with AHRI/ASHRAE/ISO 13256-1 for water-to air heat pumps and AHRI/ASHRAE/ISO 13256-2 for water-towater heat pumps. DX heat pumps shall be listed in accordance with ASHRAE 194. All heat pump equipment used in DX systems shall comply with AHRI 870. Heat pumps shall be fitted with a means to indicate that the compressor is locked out.

TABLE 1706.1

HEAT PUMPS

transfer or heat recovery shall protect the potable water system from being contaminated by the heat transfer medium. Singlewall heat exchangers shall comply with Section 1218.1. Double-wall heat exchangers shall separate the potable water from the heat transfer medium by providing a space between the two walls that are vented to the atmosphere.

shall be compatible with components with which it comes into contact. Where antifreeze or corrosion inhibitors are used, such solutions shall be approved by the Authority Having Jurisdiction. The heat-transfer fluid flash point shall be not less than 50°F (27.8°C) above the maximum system operating temperature. For DX systems, the heat transfer medium shall be a refrigerant listed in ASHRAE 34 or this code.

reach of building occupants shall not exceed 140°F (60°C) unless they are protected by insulation. Where sleeves are installed, the sleeve insulation shall retain its full size over the length of the material being protected.

shall be submitted prior to the construction of a building system, or water well. Permits shall be issued by the Authority Having Jurisdiction.

Materials. The mechanical equipment, accessories, components, and materials used shall be of the type and rating approved for the specific use.

«

«

«

«

«

The construction documents for the building system portion of the geothermal energy system shall be submitted to the Authority Having Jurisdiction.

identify the physical limitations of the land area, including its extent, structures, existing wells of all types, proximity of other existing ground source heat pump systems, pavements, trees, grading, ponds, waterways, easements, overhead and underground services, septic systems, any identified septic repair areas, utility of rights-of-way, and any other elements that could affect an open-loop configuration.

Permission shall be obtained from any adjoining property owner(s), as evidenced by the registration and approval of a formal easement that meets requirements of the Authority Having Jurisdiction. It shall be received prior to the installation of any open-loop system that will extend into, cross, or interfere with the equipment or rights-of-way of utilities, jurisdictions, and other property owners.

The site survey shall include a subsurface investigation that meets the requirements for an open-loop heat exchanger.

A subsurface investigation shall be performed in accordance with Section 1707.6 as determined by the registered design professional conducting the site survey.

other geological records shall be used to anticipate the subsurface conditions of the aquifer and its potential supply of fresh water, multiple aquifers, saltwater intrusions, contaminated soils and groundwater, hazardous gases, and any interference with neighboring water wells and ground source heat exchangers.

Geological issues such as permafrost conditions and building stability shall be considered when reviewing available records.

tices. A ground-heat exchanger system shall be installed as follows:

(1) Outside piping or tubing located within 5 feet (1524 mm) of any wall or structure shall be continuously insulated with insulation that has a minimum R-5 value. Such pipe or tubing installed under the slab or basement floors shall be insulated within 5 feet (1524 mm) from the structure to the exterior point of exit from the slab.

(2) Freeze protection shall be provided where the design of the ground-heat exchanger system would permit the heattransfer medium to freeze.

(3) Horizontal piping shall be installed not less than 12 inches (305 mm) below the frost line.

(4) Submerged heat exchangers shall be protected from damage and shall be securely fastened to the bottom of the lake or pond, or other approved submerged structure.

(5) A minimum separation distance shall be maintained between the potable water intake and the submerged heat exchanger system in accordance with the Authority Having Jurisdiction.

TABLE 1706.1

HEAT PUMPS

350 2025 CALIFORNIA MECHANICAL CODE

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

GEOTHERMAL ENERGY SYSTEMS AND AMBIENT TEMPERATURE LOOPS

«

«

«

«

«

«

«

«

«

«

«

«

«

installed for plastic and copper piping penetrating framing members to within 1 inch (25.4 mm) of the exposed framing in accordance with Section 316.6.

be fitted with end caps and protected from freezing, UV radiation, corrosion, and degradation.

lation. The heat pump and distribution system shall be installed in accordance with the system’s design, with this code, and the manufacturer’s installation instructions.

source heat pump ground loop piping to be embedded in concrete shall be pressure tested prior to pouring concrete. During pouring, the pipe shall be maintained at the proposed operating pressure.

and Methods. Horizontal geothermal piping shall be in accordance with Section 1707.17.1 through Section 1707.18.8.

1707.17.1 Piping Material. Piping materials and joining methods for horizontal piping from the ground-heat exchanger shall be in accordance with Section 1703.2, Section 1703.3, Section 1703.4, Section 1703.5 and Section 1715.3.

1707.17.2 Dissimilar Materials. Transition fittings between dissimilar materials shall be inside or accessible.

1707.17.3 Protection of Piping. Pipes passing through walls shall be sleeved and sealed in accordance with Sec tion 316.0.

for horizontal piping shall comply with Section 1707.18.1 through Section 1707.18.8, Section 1707.8 through Section 1707.11, and in accordance with the requirements of the Authority Having Jurisdiction. Prior to any excavation, trenching, or drilling, all buried utilities including drainage, and irrigation systems shall be located and flagged by the appropriate utility and ground source heat pump system contractor representative.

1707.18.1 Trenches. Trenches for underground piping or tubing shall be excavated in accordance with the setback requirements in Section 1712.4. 1707.18.2 Buried Systems. Buried open-loop system piping, shall be installed not less than 3.3 feet (1006 mm) below the finished grade.

1707.18.3 Pipe Installation. Piping in horizontal trenches shall be embedded with not less than 6 inches (152 mm) of inert granular material above and below, or in accordance with the Authority Having Jurisdiction and project specifications.

Horizontal piping trenching shall be backfilled with approved material and shall be compacted. 1707.18.4 Separation. The horizontal piping shall be separated from fluid-based onsite service systems to prevent excessive short-circuiting heat transfer between such systems.

»

»

»

»

»

(6) Vertical and horizontal ground-heat exchangers shall maintain the following setbacks:

(a) Ten feet (3048 mm) horizontally from a pressuretested sewer lateral into a building.

(b) Twenty feet (6096 mm) horizontally from a nonpressure tested sewer lateral into a building.

(c) Three feet (914 mm) horizontally from buried utilities such as electrical, gas, or water.

(d) Fifty feet (15 240 mm) from a water well.

(e) Fifty feet (15 240 mm) from a septic tank and 100 feet (30 480 mm) from a subsurface sewage leaching field.

(f) One hundred feet (30 480 mm) from a spring; or at distances specified by the Authority Having Jurisdiction.

(7) Wells and boreholes shall be sealed in accordance with the Authority Having Jurisdiction. Where grout is required, it shall be applied in a continuous operation from the bottom of the borehole by pumping through a tremie pipe.

excavation, trenching, or drilling, buried utilities, drainage, water, and irrigation systems shall be located. Prior to excavation, trenching, or drilling, the contractor, and owner shall agree in writing to site restoration requirements and submit to the Authority Having Jurisdiction for approval. Prior to any excavation, trenching, or drilling, all buried utilities including drainage and irrigation systems shall be located and flagged by the appropriate utility and ground source heat pump system contractor representative.

comply with Section 317.1. Tunneling and driving shall comply with Section 317.2.

required to be made for the installation of piping or tubing shall be in accordance with Section 317.3. Piping or tubing shall be supported to maintain its alignment and prevent sagging. Piping in the ground shall be laid on a firm bed for its entire length; where other support is otherwise provided, it shall be approved in accordance with Section 302.0. Piping or tubing shall be backfilled after an inspection in accordance with Section 317.4.

tures. Piping and tubing passing under or through walls shall be protected from breakage in accordance with Section 316.1. Piping and tubing shall be installed in accordance with Section 316.2 to provide for expansion, contraction, and structural settlement. An electrically continuous corrosion-resistant tracer wire (not less than AWG 14) or tape shall be buried with the plastic pipe to facilitate locating. One end shall be brought aboveground at a building wall or riser.

sleeves and pipes shall be sealed and made watertight and shall not be subject to a load from building construction in accordance with Section 316.7 through Section 316.7.2.

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

GEOTHERMAL ENERGY SYSTEMS AND AMBIENT TEMPERATURE LOOPS

»

»

»

»

»»

1707.18.5 Insulation. Insulation shall be provided on the piping where there is close proximity of all site services to prevent thermal interference between fluid-based onsite service systems. 1707.18.6 Pipe Bends. Sharp bending of pipe shall be prevented or approved elbow fitting shall be used with a bend-radius in accordance with the manufacturer’s

installation instructions.

1707.18.7 Closed Cell Insulation. Buried horizontal open-loop system pipes passing parallel within 5 feet (1524 mm) of a wall, structure, or water pipe shall be insulated with R-2 minimum closed cell insulation.

1707.18.8 Tracer Markings. Means shall be provided for underground detection or utility location of the buried pipe system. This shall include, but is not limited to, metallic detectable tape, with a thickness of not less than 11/64 of an inch (4.4 mm) and a width of 6 inches (152 mm).

This warning marking shall be permanent, conspicuous and resistant to the environmental conditions and shall be placed within 1 foot to 2 feet (305 mm to 610 mm) on top of the horizontal piping of the heat exchanger installation.

(1) Piping shall be cleaned, flushed, and purged.

(2) The ground-heat exchanger and building piping shall be cleaned, flushed, and, where required, shall be filled with the heat transfer fluid medium. The ground loop system shall be tested at the design flow rate(s) and differential pressure(s) recorded. Where the actual pressure change at design flow is more than +/- 10 percent of the design flow pressure drop, the cause shall be identified and corrective action taken.

(3) A method for the removal of air and a method for adding heat transfer fluid (where necessary) shall be provided.

(4) The heat pumps shall be operational and adjustments shall be made in accordance with the manufacturer’s

installation instructions.

(5) All necessary additional flow tests of the ground-heat exchanger shall be completed prior to heat pump start-up.

(6) Ground-heat exchanger and building piping, valves, and operating controls, shall be set, adjusted, and operating as required.

(7) The system shall be labeled at the loop charging valves with a permanent-type label, indicating the type of heat transfer fluid used. Where antifreeze is used, the labels shall indicate the antifreeze type and concentration.

(8) Supply and return lines, as well as associated isolation valves from individual boreholes or water wells, shall be identified and tagged.

(9) Supply and return lines on submerged systems shall be identified in an approved manner, at the point of entry to a surface water resource.

«

«

«

«

«

«

«

««

««

«

«

«

An operation and maintenance manual for the geothermal system shall be provided to the owner. The manual shall include information on required testing and maintenance of the system. Training shall be provided on the system’s operation, maintenance requirements, and on the content of the operation and maintenance manual. The operation and maintenance manual shall contain a layout of the ground-heat exchanger and building loop.

ground-loop system piping shall be marked with tape, metal tags, or other methods where it enters a building. The marking shall indicate the following words: “GROUND SOURCE HEAT PUMP-LOOP SYSTEM.” The marking shall indicate antifreeze used in the system by name and concentration.

The ground source heat pump system as-built installation drawings and instructions shall be provided to the building owner or designated agent.

in accordance with the design requirements, shall be provided and be made available to the owner or designated agent.

The ground source heat pump system construction documents shall be provided to the owner.

System start-up shall be in accordance with ANSI/ CSA/IGSHPA C448 and Section 1708.0.

removed from the indoor piping system prior to initial start up.

shall comply with ANSI/ CSA/IGSHPA C448. Prior to the abandonment or decommissioning of geothermal systems, the owner shall obtain the necessary permits from the Authority Having Jurisdiction.

Part II – Closed-Loop Systems.

geothermal closed-loop systems such as, but not limited to, building systems coupled with a closed-loop system using water-based fluid as a heat transfer medium.

Piping and tubing for closedloop systems shall be in accordance Section 1703.2 and Table 1703.2.

tubing for vertical and horizontally drilled closed-loop systems shall have a minimum wall thickness equal to SDR-11 and shall have a minimum pressure rating of not less than 160 psi (1103 kPa) at 73°F (23°C).

closed-loop systems shall be in accordance with Section 1703.3 and Table 1703.3.

352 2025 CALIFORNIA MECHANICAL CODE

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

GEOTHERMAL ENERGY SYSTEMS AND AMBIENT TEMPERATURE LOOPS

»

»

»

»

»

»

shall be flushed of debris and purged of air after completion of the entire ground-heat exchanger. Flow rates and pressure drops shall be compared to calculated values to assure no blockage or kinking of the pipe. A report shall be submitted to the owner to confirm that the loop flow is in accordance with the construction documents.

depth to provide complete insertion of the u-bend pipe to its specified depth. The borehole diameter shall be sized for the installation and placement of the heat exchange u-bend and the tremie used to place the grouting material. ANSI/ CSA/IGSHPA C448 shall be used for vertical loop depth and borehole diameter sizing guidance. The u-bend joint and pipe shall be visually inspected for integrity in accordance with the manufacturer’s installation instructions. The u-bend joint and pipe shall be pressurized to not less than 100 psi (689 kPa), not to exceed the pressure rating of the pipe at the test temperature, for 1 hour to check for leaks before insertion into the borehole.

1710.6.1 Backfill. Bentonite grout and thermallyenhanced bentonite grout, where used to seal and backfill each borehole, shall comply with NSF/ANSI/CAN 60. Boreholes shall be backfilled in accordance with the Authority Having Jurisdiction.

1710.6.2 U-Bends and Headers. Headers, u-bends and ground loop pipes shall be pressure-tested in accordance with ANSI/ CSA/IGSHPA C448, or as required by the Authority Having Jurisdiction. Before testing, heat fusion joints shall be cooled to ambient temperature. Mechanical joints shall be completely assembled. Flushing and purging to remove air and debris shall be completed before testing. The assembly shall be filled with water (or water/antifreeze solution) and purged at a minimum flow rate of 2 feet per second (0.6 m/s) to remove air, but not more than the maximum flow velocity recommended by the pipe and fittings manufacturer to remove debris.

1710.6.2.1 Test Pressure. The maximum test pressure shall be 1.5 times the system design pressure, as determined by Section 1710.6.2.3, or Section 1710.6.2.4, not to exceed 100 psi (689 kPa). Components or devices with lower pressure-ratings than the pipe shall be protected from excessive pressure during testing by removing or isolating from the test section.

Exception: Where lower pressure-rated components or devices cannot be removed or isolated from the test section, the maximum test pressure shall not exceed the pressure rating of the component or device.

1710.6.2.2 Testing Procedure. The test section and the test liquid shall be at the same temperature. The test section shall be filled with liquid and purged of air. The test section shall be brought to the specified test pressure. Test pressure shall be maintained for 4 hours, with additional fluid added as needed. The test pressure shall be reduced by 10 psi (69 kPa) and monitored for 1 hour with no addition of pres

sure or additional fluid. A passing test is indicated where after a period of 1 hour no visual leakage is observed, and pressure remains equal to or greater than 95 percent of the original pressure.

1710.6.2.3 Calculation of Static Pressure (Water). For water, the static pressure applied shall be equivalent to 0.43 psig (2.96 kPa) per foot (305 mm) of elevation.

1710.6.2.4 Calculation of Static Pressure (Other Fluids). For fluids of different density, the static pressure shall be calculated using the density of the system fluid.

exchanger shall be performed in accordance with the testing method in Section 1710.6.

loop testing shall be performed as required by the Authority Having Jurisdiction.

exchanger and building piping shall be cleaned, flushed, and, where required, shall be filled with the heat transfer fluid medium. The ground loop system shall be tested at the design flow rate(s) and differential pressure(s) recorded. Where the actual pressure change at design flow is more than +/- 10 percent of the design flow pressure drop, the cause shall be identified, and corrective action taken.

shall be performed as required by the Authority Having Jurisdiction.

Part III – Open-Loop Systems.

geothermal open-loop systems such as, but not limited to, building systems coupled with a groundwater (well) or surface water open-loop system using water-based fluid as a heat transfer medium. The regulations of this chapter shall govern the construction, location and installation of geothermal energy systems.

Indoor piping, fittings, and accessories that are part of the groundwater system shall be in accordance with Section 1703.5 and Chapter 12. Components installed in a geothermal open-loop system shall be constructed of non-ferrous or other corrosion resistant materials.

Test wells drilled to investigate subsurface conditions shall provide details of the groundwater location, chemical and physical characteristics, rock strata, and temperature profiles. The number of test wells shall be determined in accordance with the Authority Having Jurisdiction. Each test well shall be tested for flow rate for a period of not less than 24 hours. Water samples shall be collected in accor

«

«

««

«

«

«

««

«

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

GEOTHERMAL ENERGY SYSTEMS AND AMBIENT TEMPERATURE LOOPS

»

»

»»

»

»

dance with NGWA-01 from each well to establish existing water quality levels are approved for groundwater system use. Water samples shall be analyzed for standard drinking water, fecal and coliform content, bacterial iron, nitrate, dissolved minerals, pH, hardness, and other compounds in accordance with NGWA-01 or in accordance with the Authority Having Jurisdiction. Wells shall be tested for water production and recovery. Monitoring wells shall be protected, and marked to allow for monitoring of ground temperature, groundwater levels, and groundwater quality.

recharge wells, and pumping equipment shall be hydraulically tested, sealed, and grouted in accordance with approved well construction practices and submitted to the Authority Having Jurisdiction for approval. Wells shall be tested for water production and recovery, water quality before final system design. Wells shall be disinfected upon completion in accordance with NGWA-01 or in accordance with the Authority Having Jurisdiction. A copy of the water quality test results and the log of well construction in accordance with NGWA-01 shall be provided to the owner.

maintain the following minimum setbacks or at distances specified by the Authority Having Jurisdiction:

(1) Ten feet (3048 mm) horizontally from a pressure-tested sewer lateral into a building.

(2) Twenty feet (6096 mm) horizontally from a non-pressure tested sewer lateral into a building.

(3) Three feet (914 mm) horizontally from buried utilities such as electrical, gas, or water.

(4) Fifty feet (15 240 mm) from a water well.

(5) Fifty feet (15 240 mm) from a septic tank and 100 feet (30 480 mm) from a subsurface sewage leaching field.

(6) One hundred feet (30 480 mm) from a spring.

shall be in accordance with the Authority Having Jurisdiction. The water well records shall include well logs, pumping tests, and aquifer information.

well drilling logs shall include the following:

(1) The subsurface stratigraphy.

(2) The aquifer type and conditions such as, but not limited to, confined, unconfined, flowing and depth.

(3) The drilling method used and the penetration speed.

(4) The presence of substances known to have a potential risk to health and safety shall be documented in the drill logs and the property owner shall be advised of the potential risk to health and safety.

pump system shall be designed by a registered design professional. Due design consideration shall be given to the following:

(1) Where multiple heat pumps or fan coils are connected to a common water loop, a diversified building design load shall be used to design a ground water heat pump.

(2) The water supply well(s) and injection wells, or water discharge system, shall be capable of being operated at sustainable pumping rates that exceed the maximum daily requirements without causing an adverse impact to existing or future offsite uses of groundwater or surface water bodies.

(3) The water temperature and the quality and chemical composition of the water resource are in accordance with the system manufacturer’s recommendations.

(4) The groundwater and surface water resources shall be protected by returning water to the source aquifer or an aquifer with the same water quality, or a surface water body.

(5) The return capacity of the injection, or surface water body discharge system, shall be suitable under winter conditions.

(6) The temperature of the return water shall have no adverse thermal impacts on offsite existing or future uses of groundwater, or on surface water bodies, in accordance with the requirements of the Authority Having Jurisdiction.

(7) Pressure gauges shall be provided to aid in start-up and monitoring of the system during operation.

(8) The ability to switch over operation of supply and return wells for 100 percent standby, redevelopment, cleaning of wells, and the thermal balancing of the ground and aquifer shall be provided.

(9) There shall be no adverse effects on the quality and quantity of offsite existing or future users of groundwater, in accordance with the requirements of the Authority Having Jurisdiction.

and injection wells for groundwater heat pump systems shall be installed and tested by a registered design professional who is qualified to drill wells that comply with the requirements of the Authority Having Jurisdiction.

Water supply wells and injection wells shall be developed in accordance with NGWA-01.

sampling shall be done as required by the registered design professional.

completion in accordance with the requirements of the Authority Having Jurisdiction and NGWA-01.

wells shall undergo a stop and start pumping test to demonstrate the sand-free yield.

shall be corrected and the test shall be repeated until acceptable results are obtained.

«

«

«

««

«

354 2025 CALIFORNIA MECHANICAL CODE

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

GEOTHERMAL ENERGY SYSTEMS AND AMBIENT TEMPERATURE LOOPS

»

»

»

»

»

»»

»

»

»

The operating conditions of the water supply wells and injection wells shall be evaluated and verified with a variable rate pumping.

yield, aquifer coefficients, and zones of influences on the groundwater flow requirements shall be confirmed with a constant rate-pumping test. The constant rate-pumping test shall be done on the water supply and injection wells at rates and durations as specified by the registered design professional.

monitored in the pumping well and observation wells during pumping and recovery periods. The monitoring time intervals shall be as specified by the registered design professional.

on water wells that are designated to be used as injection wells at rates specified by the registered design professional. The results of the drilling and pumping tests shall be provided to the owner or the owner’s representative and provided in accordance with requirements of the Authority Having Jurisdiction.

water into the earth shall comply with the requirements of the Authority Having Jurisdiction.

Part IV – Direct Exchange (DX) Systems.

Exchange (DX) wells shall be in accordance with the Authority Having Jurisdiction. The DX well records shall include well logs, pressure tests, and aquifer information.

geothermal energy systems such as, but not limited to, building systems coupled with a DX closed-loop using refrigerant as a heat transfer medium. The regulations of this Chapter shall govern the construction, location and installation of geothermal energy systems.

Indoor piping, fittings, and accessories that are part of the ground source system shall be in accordance with Section 1703.5 and Chapter 12.

DX systems shall be manufactured in accordance with ASTM B280 and copper fittings in accordance with ASME B16.22. Joints shall be purged with an inert gas and brazed with a brazing alloy having 15 percent silver content in accordance with AWS A5.8. Underground piping and tubing shall have a cathodic protection system installed.

For direct exchange (DX) systems, each refrigerant u-bend shall be tested and proved tight with an inert gas at not less than 315 psi (2172 kPa) and maintained for 15 minutes without pressure drop. The pressure reading after tremie grouting of the boreholes shall be maintained in the ground-heat exchanger for not less than 2 hours, in accordance with ANSI/ CSA/IGSHPA C448.

purged with an inert gas and brazed with a brazing alloy having 15 percent silver content in accordance with AWS A5.8.

and fittings shall be stored to prevent physical damage, contamination, and each pipe or tubing shall be pressurized with an inert gas and sealed with a cap.

accordance with Section 1708.1 and the following:

(1) DX systems shall be pressurized using nitrogen for not less than 1 hour. There shall be no allowable variance to

the test pressure after being corrected for ambient temperature changes during the test. The test pressure shall not exceed 150 psig (1034 kPa) when pressure testing the compressor unit and indoor system components.

(2) DX systems shall have permanent type labels installed and affixed on the compressor unit with the refrigerant type and quantity.

(3) For DX systems, refrigerant liquid and vapor lines from the loop system shall be identified and tagged.

DX Piping should be installed in accordance with approved plans and specifications, including provisions for cathodic protection.

Part V – Geothermal Ambient Temperature Loops (ATL).

Energy Systems.

An Ambient Temperature Loop (ATL) distributed energy system shall be installed in accordance with Section 1716.1.1 through Section 1716.6.3 and Section 1717.0. ATL systems shall comply with Part I through Part IV of this chapter, as applicable.

1716.1.1 Fourth Generation (4G) System Config- uration. A fourth-generation system configuration shall be a district geothermal energy system distributing hot water, cold water, or both to the conditioned space or building for a specific use. Where a geothermal energy source is used, such system shall comply with Part I through Part IV of this chapter, Chapter 11, and Chapter 12.

1716.1.2 Fifth Generation (5G) System Configu- rations. An advanced Ambient Temperature Loop (ATL) System or fifth generation (5G) ATL system shall also be capable of interacting with the electric utility system as well as other utility systems and systems compo nents.

The system components shall include, but not limited to, the following:

(1) Thermally diverse buildings with independent hydronic systems

«

«

«

«

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

GEOTHERMAL ENERGY SYSTEMS AND AMBIENT TEMPERATURE LOOPS

(2) Circulation loop

(3) Global control system

(4) Segment isolation capability

The system components may include, but not limited to, the following:

(1) Electric grid-interactive enabled buildings

(2) Hybrid components

(3) Other renewable systems

application of an ATL distributed energy system shall be obtained as required by the Authority Having Jurisdiction.

The operating loop temperature range of an ambient temperature loop (ATL) system shall be not less than the freeze point of the circulating fluid and not more than the maximum temperature as required by the manufacturer’s installation instructions for the attached heat pump equipment in accordance with Section 1716.3.1 and Section 1716.3.2. The ATL system shall use treated water as the heat transfer medium.

1716.3.1 ATL Operating Temperature. For equipment listed to AHRI/ASHRAE/ISO 13256-1 and AHRI/ASHRAE/ISO 13256-2, the controlled temperature range of the ambient closed loop shall be not less than 7°F (4°C) above the freeze point of the transport fluid and 10°F (6°C) below the (collective) heat pump lowest maximum inlet supply temperature as recommended by the manufacturer’s instructions.

Exception: Equipment that is not listed to AHRI/ASHRAE/ISO 13256-1 and AHRI/ASHRAE/ISO 13256-2. The controlled temperature range of the ambient closed loop shall be in accordance with Section 1716.3.2 for minimum and maximum temperatures.

1716.3.2 ATL Operating Temperature Range for Mixed Equipment Certifications. The source inlet temperature range of any attached equipment shall govern the design operating temperature range. Such equipment shall be identified in the design documentation. In any case the most restrictive minimum and maximum inlet supply temperatures, as recommended by the manufacturer’s instructions, shall determine the system operating temperature range.

provided for each individual building or facility transferring energy to or from an ATL distribution system. The automatic shutoff valve shall automatically shutoff upon operating command.

1716.4.1 Shutoff Valve Operation. The operation of the automatic shutoff valve shall be in accordance with the system operating procedures. Where the operation of a shutoff valve was due to an emergency response, an auxiliary heating or cooling methodology shall be provided in accordance with Section 1717.1.2.

be provided with bypass path(s) to reroute the circulating fluid when necessary.

design, meter(s) shall be located as specified by the manufacturer on each consumptive or supply source and the range of the metering shall be appropriate to the thermal properties and flow rate(s) of the transport fluid.

1716.6.1 Sub-Metering System Specification. The entire energy measurement system shall be provided with a sub-metering system. The metering system shall be calibrated and shall consist of a flow meter, temperature sensors, temperature thermowells, or other required mechanical installation metering. The sub-meter traceable calibration shall comply with the National Institute of Standards Technology (NIST) traceable calibration program or in accordance with the Authority Having Jurisdiction and shall be provided with an ATL distributed energy system.

1716.6.2 BTU/Thermal Meters. Where used, the Btu/thermal meter shall be bidirectional and shall provide the following information via digital or analog display:

(1) LCD, and via serial network communications.

(2) Total energy.

(3) Energy rate.

(4) Total flow.

(5) Flow rate.

(6) Supply temperature.

(7) Return temperature.

Each Btu/thermal meter shall be factory programmed for its specific application and shall be re-programmable to adjust for specific site conditions.

1716.6.3 Flow Meter. Where used, the flow meter shall be provided with the following information via digital or analog display:

(1) LCD, and via serial network communications.

(2) Instantaneous fluid rate.

(3) Cumulative fluid flow volume.

Requirements.

shall be permitted to connect to a thermal resource(s). Such resources may be an alternative energy source and sink, such as but not limited to solar photovoltaic (PV), solar thermal, combined heat power (CHP), and phase change thermal storage. These systems shall be installed and comply with the respective system requirements. ATL distributed energy systems coupled with solar thermal systems shall comply with the Uniform, Solar, Hydronics and Geothermal Code (USHGC) or equivalent. ATL systems coupled with a solar PV system shall comply with the USHGC or NFPA 70, or equivalent. These systems shall optimize the use of the equipment and energy based on the system design intent.

1717.1.1 System Performance. The System Coefficient of Performance (SCOP) of the system shall take the

356 2025 CALIFORNIA MECHANICAL CODE

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

GEOTHERMAL ENERGY SYSTEMS AND AMBIENT TEMPERATURE LOOPS

net COP of each individual members in the district. The SCOP shall be provided by the designer and included in the system design documents.

1717.1.2 Emergency Response. An auxiliary heating or cooling methodology shall be provided with the ATL controls and shall be adequate to provide temporary service in the absence of an ATL energy transfer. Emergency source/sink measures such as but not limited to control subroutines that move energy between spaces in the building, use of locally connected ground source assets, combined heat and power (CHP), conventional equipment, other renewables systems may be used.

an ambient temperature loop (ATL) distributed energy system shall be identified and shall be included in the basis-of-design (BOD).

1717.2.1 System Asset Identification. System assets shall be listed and included in the system design. The system asset shall include, but not be limited to, the following:

(1) Building type and quantity.

(2) Natural or constructed sources and sinks such as ground water, boreholes, etc.

(3) Other renewable assets.

(4) Wasted heat recovery.

(5) Potable and non-potable water or fluid sources.

(6) Conventional assets such as boilers and cooling tow ers.

(7) Other GeoMicroDistrict or thermal highway.

1717.2.2 Driver Building. The driver building profile shall be identified in an ATL distributed energy system and shall be reported in the design documents.

1717.2.3 Diversity Factor. The diversity factor and/or anticipated wasted energy recovery component of the GeoMicroDistrict shall be identified by the designer and this information shall be included in the drawings and specifications.

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

358 2025 CALIFORNIA MECHANICAL CODE

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

CALIFORNIA MECHANICAL CODE – MATRIX ADOPTION TABLE