CMC · California Mechanical Code

How to size and install expansion tanks for closed hydronic systems

Q: Can I isolate the expansion tank with a shutoff valve for servicing?

You may have a shutoff device, but the code requires it remain open during operation ; handles must be locked open or removed to prevent accidental isolation (see § 1209.2 ) .

Q: What if the system design pressure is over 30 psi?

If the system operates at more than 30 psi , the expansion tank must comply with ASME BPVC Section VIII.1 (see § 1209.3 ) .

Q: How do I find the exact minimum tank capacity required by code?

The CMC requires sizing per § 1004.4 (Chapter 10), which contains the official tables and equations for the minimum capacity of closed‑type tanks; consult those tables or the manufacturer’s sizing charts and the code for the final selection (see § 1209.4 and § 1004.4 ) .

Q: What support design is required for the tank?

Supports must be capable of carrying twice the weight of the tank filled with water without putting strain on connecting piping (see § 1209.2 ) .

Your hydronic system must have a closed expansion tank sized to accept the system’s full thermal expansion, installed per the manufacturer and CMC. The tank must be accessible, supported for twice its filled weight, have a shutoff that stays open, meet hydrostatic/ASME requirements if pressures exceed 30 psi, and its minimum capacity must follow §1004.4 as required by §1209.4 of the CMC.

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Last reviewed: July 6, 2026

What the code requires — 2–4 sentences

An expansion tank must be installed in every closed hydronic system to control pressure created by thermal expansion; tanks must be closed-type and rated for the system pressure (see § 1209.1). Installation must allow maintenance access, follow the manufacturer’s instructions, include a shutoff device that is kept open, provide a way to drain the tank without emptying the system, and support the filled tank load (see § 1209.2). Closed-type tanks must meet hydrostatic test strength and, if the system is designed to operate above 30 psi, comply with ASME BPVC Section VIII.1 (see § 1209.3 and § 1209.4) .

The single most important rule: install a closed expansion tank sized to accept the system’s full expansion volume, accessible for maintenance, supported for twice its filled weight, and installed per the manufacturer and the code (see § 1209.1, § 1209.2, § 1209.4) .

Note on citations

All code requirements below are grounded in the California Mechanical Code sections § 1209.0–§ 1209.4 and the sizing cross-reference to § 1004.4; each subsection below cites the specific controlling § and the file source identified by the retrieved code text .

Requirements in detail

1) General requirement (what must exist)

An expansion tank shall be installed in each closed hydronic system to control system pressure due to thermal expansion and contraction. Tanks shall be closed-type and rated for the pressure of the system (controlling: § 1209.1) .

2) Installation and accessibility

The tank must be accessible for maintenance and installed per the manufacturer’s installation instructions (see § 1209.2) .
Each expansion tank must have a shutoff device that remains open during operation; valve handles shall be locked open or removed to prevent inadvertent shutoff (see § 1209.2) .
Provisions must be made for draining the tank without emptying the system (see § 1209.2) .
Tanks must be securely fastened or supported; supports must be capable of carrying twice the weight of the tank filled with water without placing strain on connecting piping (see § 1209.2 and related §1004.1) .

3) Construction / strength requirements for closed tanks

Closed-type expansion tanks shall be designed for a hydrostatic test pressure of 2½ times the allowable working pressure of the system (see § 1209.3) .
If the system is designed to operate at more than 30 psi (207 kPa), the expansion tank must comply with ASME BPVC Section VIII.1 (see § 1209.3) .

4) Sizing: accept full expansion volume

Expansion tanks must be sized to accept the full expansion volume of the fluid in the system; the minimum capacity of a closed-type expansion tank is sized in accordance with Section 1004.4 (see § 1209.4) .
Section 1004.4 (Chapter 10) contains the code’s tables and equations (for gravity, forced, and diaphragm tanks) and defines variables such as Vt (tank volume), Vs (system volume), t (average operating temperature), Pf (fill pressure), and Po (maximum operating pressure) that are used for computing minimum tank capacity (see § 1004.4) .

Quick decision table (decision‑relevant dimensions / values)

Decision item	Requirement / typical value	Code Reference
Tank type	Closed-type for closed hydronic systems	§ 1209.1
Accessible & per manufacturer	Tank accessible; install per instructions; drain without emptying system	§ 1209.2
Shutoff device	Shutoff allowed but must remain open during operation; handles locked/removed	§ 1209.2
Supports	Supports must carry twice the filled tank weight without stressing piping	§ 1209.2 / § 1004.1
Hydrostatic test	Tank must be tested at 2½ × allowable working pressure	§ 1209.3
ASME compliance	If system operating pressure > 30 psi, tank must comply with ASME BPVC Sec. VIII.1	§ 1209.3
Minimum tank capacity	Sized to accept full expansion volume; minimum per § 1004.4	§ 1209.4 / § 1004.4

Exceptions & special cases

Systems designed to operate above 30 psi: tanks must comply with ASME BPVC Section VIII.1 (see § 1209.3) .
Hot-water-heating systems incorporating hot water tanks or fluid relief columns must be installed to prevent freezing under normal operating conditions (see § 1209.2) .
Secondary loops isolated by a heat exchanger are treated as closed-loop hydronic systems and shall have an expansion tank in accordance with § 1209.0 (see § 1214.8) .
Manufacturer instructions and listings control installation details: the code requires following those instructions (see § 1209.2) .

Common mistakes

Leaving the shutoff valve on the tank closed (or installable): the code requires the shutoff device to remain open and handles locked/removed (see § 1209.2) .
Undersizing by using only a rule‑of‑thumb instead of sizing to accept full expansion volume and checking § 1004.4 minimums (see § 1209.4) .
Inadequate supports: not designing supports to carry twice the weight of the full tank can place strain on piping (see § 1209.2) .
Ignoring hydrostatic test / ASME requirements when system pressures exceed 30 psi (see § 1209.3) .
Not providing a way to drain the tank without emptying the whole system (required by § 1209.2) .

Worked example — concrete scenario applying the rule with numbers

Note: § 1209.4 requires sizing “to accept the full expansion volume” and points to § 1004.4 for the code’s tables and equations; the code text for the tables/equations in § 1004.4 was retrieved but the full printed tables are not reproduced here. Below is an illustrative calculation that follows the same variable definitions used by the code (Vs, Pf, Po) and common diaphragm‑tank math; this demonstrates the method. Always confirm final tank size against the manufacturer’s chart or the official § 1004.4 tables/equation in the code before installing (see § 1209.2 and § 1209.4) .

Scenario:

System water volume (Vs): 100 gallons
Cold/fill temperature: 60°F
Maximum operating temperature: 180°F
Fill (precharge) pressure (Pf): 12 psi
Maximum operating (relief or design) pressure (Po): 30 psi
Atmospheric pressure (Pa): 14.7 psi (standard)

Step 1 — estimate expansion volume (Ve):

For water heated from 60°F to 180°F, typical volumetric expansion is roughly 2.2% (0.022) — this is a common engineering approximation for this temperature range (confirm with actual fluid properties for exact projects).
Ve = Vs × expansion fraction = 100 gal × 0.022 = 2.2 gallons (this is the fluid expansion to be accepted by the tank).

Step 2 — convert expansion volume to required tank volume (diaphragm tank math):

A diaphragm tank’s usable acceptance volume depends on fill and maximum pressures. One commonly used relationship (same variable names used in the code’s § 1004.4) is: Vt = Ve × (Po + Pa) / (Po − Pf) (This aligns with the variables defined in § 1004.4: Po = maximum operating pressure; Pf = fill pressure; Pa = atmospheric pressure) .
Numerically:
- Po + Pa = 30 + 14.7 = 44.7
- Po − Pf = 30 − 12 = 18
- Multiplier = 44.7 / 18 ≈ 2.483
- Required tank volume Vt = 2.2 gal × 2.483 ≈ 5.46 gallons

Step 3 — select the next standard tank size and verify minimums:

Choose the next commonly available tank size above calculated Vt; for this example you would select an 8‑gallon precharged diaphragm tank.
Verify that the chosen tank’s rated pressure equals or exceeds the system’s maximum working pressure, that it meets hydrostatic/ASME requirements if Po > 30 psi, and that supports can carry twice the filled weight (see § 1209.2 and § 1209.3) .

Important: this worked example is illustrative and uses a typical expansion fraction. The CMC refers you to § 1004.4 (tables/equations) for the code minimum capacity calculations and to the tank manufacturer’s sizing chart; you must use those definitive sources on a real project (see § 1209.4 and § 1209.2) .

Related provisions (CMC sections)

§ 1209.1 — General expansion tank requirement for closed hydronic systems (see text) .
§ 1209.2 — Installation and maintenance/ support / shutoff device requirements .
§ 1209.3 — Closed-type tank hydrostatic test and ASME compliance when > 30 psi .
§ 1209.4 — Sizing requirement; points to § 1004.4 for minimum capacity calculations .
§ 1004.3 — Closed-type system strength and test-pressure criteria (Chapter 10) .
§ 1004.4 — Code tables/equations for minimum closed-type expansion tank capacity (Chapter 10); defines Vt, Vs, Pf, Po and the sizing equations/tables used by the CMC .
§ 1214.8 — Secondary loops (isolated by heat exchangers) require an expansion tank in accordance with § 1209.0 .
§ 1210.3 — Hangers and supports (relevant to supporting tanks and piping) .

Code references

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

CMC § 1211.2.2 High relevance — show source text
1211.2.2 Polyethylene (PE) Plastic Pipe/Tubing. Polyethylene pipe and tubing bends shall have a bend radius in accordance with Table 1211.2.2. When a fitting or flange connection is present in the pipe bend, the minimum bend radius shall be one hundred times the pipe outside diameter (OD) for a distance of five times the pipe diameter on either side of the fitting location.

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1208.2 Mounting. The circulator or pump shall be installed in such a way that strain from the piping is not transferred to the circulator or pump housing. The circulator or pump shall be permitted to be directly connected to the piping, provided the piping is supported on each side of the circulator or pump. Where the installation of a circulator or pump will cause strain on the piping, the circulator or pump shall be installed on a mounting bracket or base plate or securely fastened to or supported by the structure with approved fastening devices. Where means for controlling vibration of a circulator or pump is required, an approved means for support and restraint shall be provided. 1208.3 Sizing. The selection and sizing of a circulator or pump shall be based on all of the following: (1) Loop or system head pressure, feet of head (m) (2) Capacity, gallons per minute (L/s) (3) Maximum and minimum temperature, °F (°C) (4) Maximum working pressure, pounds per square inch (kPa) (5) Fluid type

1209.0 Expansion Tanks. 1209.1 General. An expansion tank shall be installed in each closed hydronic system to control system pressure due to thermal expansion and contraction. Expansion tanks shall be of the closed type. Expansion tanks shall be rated for the pressure of the system. 1209.2 Installation. Expansion tanks shall be accessible for maintenance and shall be installed in accordance with the manufacturer’s installation instructions. Each expansion tank shall be equipped with a shutoff device that will remain open during operation of the hydronic system. Valve handles shall be locked open or removed to prevent from being inadvertently shut off. Provisions shall be made for draining the tank without emptying the system. Expansion tanks shall be securely fastened to or supported by the structure. Supports shall be capable of carrying twice the weight of the tank filled with water without placing a strain on connecting piping. Hot-water-heating systems incorporating hot water tanks or fluid relief columns shall be installed to prevent freezing under normal operating conditions. 1209.3 Closed-Type Tanks. Closed-type expansion tanks shall be designed for a hydrostatic test pressure of two and one-half times the allowable working pressure of the system. Expansion tanks for systems designed to operate at more than 30 pounds-force per square inch (psi) (207 kPa) shall comply with ASME BPVC Section VIII.1.

1209.4 Sizing. Expansion tanks shall be sized to accept the full expansion volume of the fluid in the system. The minimum capacity of a closed-type expansion tank shall be sized in accordance with Section 1004.4.

1210.0 Materials.

1210.1 Piping, Tubing, and Fittings. Hydronic pipe and tubing shall comply with the applicable standards referenced in Table 1210.1 and shall be approved for use based on the intended purpose. Materials shall be rated for the operating

260 2025 CALIFORNIA MECHANICAL CODE

CMC § 1209.2 High relevance — show source text

Expansion tanks shall be of the closed type. Expansion tanks shall be rated for the pressure of the system. 1209.2 Installation. Expansion tanks shall be accessible for maintenance and shall be installed in accordance with the manufacturer’s installation instructions. Each expansion tank shall be equipped with a shutoff device that will remain open during operation of the hydronic system. Valve handles shall be locked open or removed to prevent from being inadvertently shut off. Provisions shall be made for draining the tank without emptying the system. Expansion tanks shall be securely fastened to or supported by the structure. Supports shall be capable of carrying twice the weight of the tank filled with water without placing a strain on connecting piping. Hot-water-heating systems incorporating hot water tanks or fluid relief columns shall be installed to prevent freezing under normal operating conditions. 1209.3 Closed-Type Tanks. Closed-type expansion tanks shall be designed for a hydrostatic test pressure of two and one-half times the allowable working pressure of the system. Expansion tanks for systems designed to operate at more than 30 pounds-force per square inch (psi) (207 kPa) shall comply with ASME BPVC Section VIII.1.

1209.4 Sizing. Expansion tanks shall be sized to accept the full expansion volume of the fluid in the system. The minimum capacity of a closed-type expansion tank shall be sized in accordance with Section 1004.4.

1210.0 Materials.

1210.1 Piping, Tubing, and Fittings. Hydronic pipe and tubing shall comply with the applicable standards referenced in Table 1210.1 and shall be approved for use based on the intended purpose. Materials shall be rated for the operating

260 2025 CALIFORNIA MECHANICAL CODE

HYDRONICS

TABLE 1210.1

MATERIALS FOR HYDRONIC SYSTEM PIPING, TUBING, AND FITTINGS

MATERIAL	STANDARDS	Col3
MATERIAL	PIPING/TUBING	FITTINGS
Copper/Copper Alloy	ASTM B42, ASTM B43, ASTM B75, ASTM B88, ASTM B135, ASTM B2512, ASTM B302, ASTM B447	ASME B16.15, ASME B16.18, ASME B16.22, ASME B16.23, ASME B16.24, ASME B16.26, ASME B16.29, ASME B16.51, ASSE 1061, ASTM F3226, IAPMO PS 117
Ductile Iron	AWWA C115/A21.15, AWWA C151/A21.51	AWWA C110/A21.101, AWWA C153/A21.53
Steel	ASTM A53, ASTM A106, ASTM A254	ASME B16.5, ASME B16.9, ASME B16.11, ASTM A420, ASTM F3226, IAPMO IGC 353, IAPMO PS 117
Stainless Steel	ASTM A269, ASTM A312, ASTM A554, ASTM A778	ASTM F1476, ASTM F1548, ASTM F3226, IAPMO IGC 353,

CMC § 608.3 High relevance — show source text
The expansion tank shall be properly sized, securely fastened to the structure, and installed in accordance with the manufacturer’s installation instructions and listing. Systems designed by a licensed plumbing contractor or registered design professionals shall be permitted to use approved pressure relief valves in lieu of expansion tanks provided such relief valves have a maximum pressure relief setting of 100 psi (689 kPa) or less. 608.3 Expansion Tanks, and Combination Tempera- ture and Pressure-Relief Valves. A water system provided with a check valve, backflow preventer, or other normally closed device that prevents dissipation of building pressure back into the water main, independent of the type of water heater used, shall be provided with an approved, listed, and adequately sized expansion tank or other approved device having a similar function to control thermal expansion. Prepressurized water expansion tanks shall comply with IAPMO/ANSI Z1088. Such expansion tank or other approved device shall be installed on the building side of the check valve, backflow preventer, or other device and shall be sized, securely fastened to the structure, and installed in accordance with the manufacturer’s installation instructions.

A water system containing storage water heating equipment shall be provided with an approved, listed, adequately sized combination temperature and pressure-relief valve, except for listed nonstorage instantaneous heaters having an inside diameter of not more than 3 inches (80 mm). Each such approved combination temperature and pressure-relief valve shall be installed on the water-heating device in an approved location based on its listing requirements and the manufacturer’s installation instructions. Each such combination temperature and pressure-relief valve shall be provided with a drain in accordance with Section 608.5.

Exception: An expansion tank shall not be required for an instantaneous non-storage water heater. 608.4 Pressure Relief Valves. Each pressure relief valve shall be an approved automatic type with drain, and each such relief valve shall be set at a pressure of not more than 150 psi (1034 kPa). No shutoff valve shall be installed between the relief valve and the system. 608.5 Discharge Piping. The discharge piping serving a temperature relief valve, pressure relief valve, or combination of both shall have no valves, obstructions, or means of isolation and be provided with the following:

(1) Not less than the size of the valve outlet and shall discharge full size to the flood level of the area receiving the discharge and pointing down.

(2) Materials shall be rated at not less than the operating temperature of the system and approved for such use or shall comply with ASME A112.4.1.

(3) Discharge pipe shall discharge independently by gravity through an air gap into the drainage system or outside of the building with the end of the pipe not exceeding 2 feet

154 2025 CALIFORNIA PLUMBING CODE

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

WATER SUPPLY AND DISTRIBUTION

(610 mm) and not less than 6 inches (152 mm) above the ground and pointing downwards.

(4) Discharge in such a manner that does not cause personal injury or structural damage. (5) No part of such discharge pipe shall be trapped or subject to freezing. (6) The terminal end of the pipe shall not be threaded. (7) Discharge from a relief valve into a water heater pan shall be prohibited. (8) The discharge termination point shall be readily observable.
CMC § 610.4. High relevance — show source text
** Where static water pressure in the water supply piping exceeds 80 psi (552 kPa), an approved-type pressure regulator preceded by an adequate strainer shall be installed and the static pressure reduced to 80 psi (552 kPa) or less. Pressure regulators for potable water distribution systems shall comply with ASSE 1003 or AWWA C530. Pressure regulator(s) equal to or exceeding 1 [1] ⁄ 2 inches (40 mm) shall not require a strainer. Such regulator(s) shall control the pressure to water outlets in the building unless otherwise approved by the Authority Having Jurisdiction. Each such regulator and strainer shall be accessibly located aboveground or in a vault equipped with a properly sized and sloped boresighted drain to daylight, shall be protected from freezing, and shall have the strainer readily accessible for cleaning without removing the regulator or strainer body or disconnecting the supply piping. Pipe size determinations shall be based on 80 percent of the reduced pressure where using Table 610.4.

An approved expansion tank shall be installed in the cold water distribution piping downstream of each such regulator to prevent pressure exceeding 80 psi from developing due to thermal expansion. Expansion tanks used in potable water systems intended to supply drinking water shall comply with NSF/ANSI/CAN 61. The expansion tank shall be properly sized, securely fastened to the structure, and installed in accordance with the manufacturer’s installation instructions and listing. Systems designed by a licensed plumbing contractor or registered design professionals shall be permitted to use approved pressure relief valves in lieu of expansion tanks provided such relief valves have a maximum pressure relief setting of 100 psi (689 kPa) or less. 608.3 Expansion Tanks, and Combination Tempera- ture and Pressure-Relief Valves. A water system provided with a check valve, backflow preventer, or other normally closed device that prevents dissipation of building pressure back into the water main, independent of the type of water heater used, shall be provided with an approved, listed, and adequately sized expansion tank or other approved device having a similar function to control thermal expansion. Prepressurized water expansion tanks shall comply with IAPMO/ANSI Z1088. Such expansion tank or other approved device shall be installed on the building side of the check valve, backflow preventer, or other device and shall be sized, securely fastened to the structure, and installed in accordance with the manufacturer’s installation instructions.

A water system containing storage water heating equipment shall be provided with an approved, listed, adequately sized combination temperature and pressure-relief valve, except for listed nonstorage instantaneous heaters having an inside diameter of not more than 3 inches (80 mm). Each such approved combination temperature and pressure-relief valve shall be installed on the water-heating device in an approved location based on its listing requirements and the manufacturer’s installation instructions. Each such combination temperature and pressure-relief valve shall be provided with a drain in accordance with Section 608.5.
California Mechanical Code High 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.
CMC § 1003.2.1. High relevance — show source text
be equipped with controls and limit devices in accordance with ASME CSD-1 or Table 1003.2.1.

The Authority Having Jurisdiction shall have the authority to approve solid-fuel-fired boilers that comply with the safety requirements for automatic gas fired boilers or oil fired boilers.

1003.3 Gauges. Steam boilers shall be provided with a pressure gauge and a water level glass. Water boilers shall be provided with a pressure gauge and a temperature gauge. Automatic boilers shall be equipped with the following gauges, as applicable :

(1) Oil temperature

(2) Oil suction pressure

(3) High and low gas pressure

(4) Stack temperature

(5) Windbox pressure

1003.4 Stack Dampers. Stack dampers on boilers fired with oil or solid fuel shall not close off more than 80 percent of the stack area. Operative dampers shall not be placed within a stack, flue, or vent of a gas-fired boiler.

Exception: Automatic boilers with prepurge, automatic draft control, and interlock.

1003.5 Welding. Welding on pressure vessels shall be done by certified welders in accordance with nationally recognized standards.

1004.0 Expansion Tanks.

1004.1 General. An expansion tank shall be installed in a hot-water-heating system as a means for controlling increased pressure caused by thermal expansion. Expansion tanks shall be of the closed or open type and securely fastened to or supported by the structure. Tanks shall be rated for the pressure of the system. Supports shall be capable of carrying twice the weight of the tank filled with water without placing a strain on connecting piping.

Hot-water-heating systems incorporating hot water tanks or fluid relief columns shall be installed to prevent freezing under normal operating conditions.

1004.2 Open-Type Expansion Tanks. Open type expansion tanks shall be located not less than 3 feet (914 mm) above the highest point of the system. Such tanks shall be sized based on the capacity of the system. An overflow with a diameter of not less than one-half the size of the supply or not less than 1 inch (25 mm) in diameter shall be installed at the top of the tank. The overflow shall discharge through an air gap into the drainage system.

1004.3 Closed-Type Systems. Closed-type systems shall have an airtight tank or other approved air cushion that will be consistent with the volume and capacity of the system, and shall be designed for a hydrostatic test pressure of two and one-half times the allowable working pressure of the system. Expansion tanks for systems designed to operate at more than 30 pounds-force per square inch (psi) (207 kPa) shall comply with ASME BPVC Section VIII.1. Provisions shall be made

for draining the tank without emptying the system.

1004.4 Minimum Capacity of Closed-Type Tank. The minimum capacity for a gravity-type hot water system expansion tank shall be in accordance with Table 1004.4(1). The minimum capacity for a forced-type hot water system expansion tank shall be in accordance with Table 1004.4(2) or Equation 1004.4(1). The minimum capacity for a diaphragmtype hot water system expansion tank shall be in accordance with Table 1004.4(2) or Equation 1004.4(2).

[Equation 1004.4(1)]

Vt (forced-type) = [(0.00041] [t] [ - 0.0466) ] [V][s]

(
CMC § 1206.2 High relevance — show source text
1206.2 Discharge Piping . . . . . . . . . . . . . 259

1207.0 Heating Appliances and Equipment . . . . . . . . . . . . . . . . . . 259

1207.1 General. . . . . . . . . . . . . . . . . . . . . 259

1207.2 Boilers. . . . . . . . . . . . . . . . . . . . . . 259

1207.3 Dual Purpose Water Heaters . . . . 259

1207.4 Solar Heat Collector Systems. . . . 259

1207.5 Heat Pumps . . . . . . . . . . . . . . . . . 259

1208.0 Circulators and Pumps . . . . . . . . . 259

1208.1 General. . . . . . . . . . . . . . . . . . . . . 259

1208.2 Mounting. . . . . . . . . . . . . . . . . . . . 260

1208.3 Sizing . . . . . . . . . . . . . . . . . . . . . . 260

1209.0 Expansion Tanks . . . . . . . . . . . . . 260

1209.1 General. . . . . . . . . . . . . . . . . . . . . 260

1209.2 Installation . . . . . . . . . . . . . . . . . . 260

1209.3 Closed-Type Tanks . . . . . . . . . . . 260

1209.4 Sizing . . . . . . . . . . . . . . . . . . . . . . 260

1210.0 Materials . . . . . . . . . . . . . . . . . . . . 260

1210.1 Piping, Tubing, and Fittings . . . . . 260

1210.2 Expansion and Contraction . . . . . . 260

1210.3 Hangers and Supports . . . . . . . . . 260

1210.4 Oxygen Diffusion Corrosion . . . . . 260

1211.0 Joints and Connections . . . . . . . . 260

1211.1 General. . . . . . . . . . . . . . . . . . . . . 260

1211.2 Pipe Bends . . . . . . . . . . . . . . . . . . 260

Table 1210.1 Materials for Hydronic System Piping, Tubing, and Fittings . . . . . 261

Table 1211.2.2 Minimum Bend Radius

for PE Pipe Installed in Open Cut Trench . . . . . . . . . . . . . 262

1211.3 Chlorinated Polyvinyl Chloride (CPVC) Pipe . . . . . . . . . . . . . . . . . 262

1211.4 CPVC/AL/CPVC Plastic Pipe and Joints . . . . . . . . . . . . . . . . . . . 262

2025 CALIFORNIA MECHANICAL CODE

1211.5 Copper or Copper Alloy Pipe and Tubing . . . . . . . . . . . . . . . . . . 262
CMC § 607.5 Medium relevance — show source text
installation instructions. Such vent shall be screened with a cor rosion-resistant material of not less than number 24 mesh.

607.5 Overflow. Tanks shall have not less than a 16 square inch (0.01 m [2] ) overflow that is screened with a corrosionresistant material of not less than number 24 mesh.

607.6 Valves. Pressurized tanks shall be provided with a listed pressure-relief valve installed in accordance with the manufacturer’s installation instructions. The relief valve shall be discharged in accordance with Section 608.5. Where a potable water supply tank is located above the fixtures, appliances, or system components it serves, it shall be equipped with a vacuum relief valve that complies with ANSI Z21.22/CSA 4.4.

608.0 Water Pressure, Pressure Regulators, Pres- sure Relief Valves, and Vacuum Relief Valves. 608.1 Inadequate Water Pressure. Where the water pressure in the main or other source of supply will not provide a residual water pressure of not less than 15 pounds force per square inch (psi) (103 kPa), after allowing for friction and other pressure losses, a tank and a pump or other means that will provide said 15 psi (103 kPa) pressure shall be installed. Where fixtures, fixture fittings, or both are installed that, require a residual pressure exceeding 15 psi (103 kPa), that minimum residual pressure shall be provided.

608.2 Excessive Water Pressure. Where static water pressure in the water supply piping exceeds 80 psi (552 kPa), an approved-type pressure regulator preceded by an adequate strainer shall be installed and the static pressure reduced to 80 psi (552 kPa) or less. Pressure regulators for potable water distribution systems shall comply with ASSE 1003 or AWWA C530. Pressure regulator(s) equal to or exceeding 1 [1] ⁄ 2 inches (40 mm) shall not require a strainer. Such regulator(s) shall control the pressure to water outlets in the building unless otherwise approved by the Authority Having Jurisdiction. Each such regulator and strainer shall be accessibly located aboveground or in a vault equipped with a properly sized and sloped boresighted drain to daylight, shall be protected from freezing, and shall have the strainer readily accessible for cleaning without removing the regulator or strainer body or disconnecting the supply piping. Pipe size determinations shall be based on 80 percent of the reduced pressure where using Table 610.4.

An approved expansion tank shall be installed in the cold water distribution piping downstream of each such regulator to prevent pressure exceeding 80 psi from developing due to thermal expansion. Expansion tanks used in potable water systems intended to supply drinking water shall comply with NSF/ANSI/CAN 61. The expansion tank shall be properly sized, securely fastened to the structure, and installed in accordance with the manufacturer’s installation instructions and listing. Systems designed by a licensed plumbing contractor or registered design professionals shall be permitted to use approved pressure relief valves in lieu of expansion tanks provided such relief valves have a maximum pressure relief setting of 100 psi (689 kPa) or less. 608.3 Expansion Tanks, and Combination Tempera- **ture and Pressure-Relief Valves.
CMC § 1004.2 Medium relevance — show source text
1004.2 Open-Type Expansion Tanks. Open type expansion tanks shall be located not less than 3 feet (914 mm) above the highest point of the system. Such tanks shall be sized based on the capacity of the system. An overflow with a diameter of not less than one-half the size of the supply or not less than 1 inch (25 mm) in diameter shall be installed at the top of the tank. The overflow shall discharge through an air gap into the drainage system.

1004.3 Closed-Type Systems. Closed-type systems shall have an airtight tank or other approved air cushion that will be consistent with the volume and capacity of the system, and shall be designed for a hydrostatic test pressure of two and one-half times the allowable working pressure of the system. Expansion tanks for systems designed to operate at more than 30 pounds-force per square inch (psi) (207 kPa) shall comply with ASME BPVC Section VIII.1. Provisions shall be made

for draining the tank without emptying the system.

1004.4 Minimum Capacity of Closed-Type Tank. The minimum capacity for a gravity-type hot water system expansion tank shall be in accordance with Table 1004.4(1). The minimum capacity for a forced-type hot water system expansion tank shall be in accordance with Table 1004.4(2) or Equation 1004.4(1). The minimum capacity for a diaphragmtype hot water system expansion tank shall be in accordance with Table 1004.4(2) or Equation 1004.4(2).

[Equation 1004.4(1)]

Vt (forced-type) = [(0.00041] [t] [ - 0.0466) ] [V][s]

(

P P a a

Pf Po )

[Equation 1004.4(2)]

Vt (diaphragm-type) = [(0.00041] [t] [ - 0.0466) ] [V][s]

– [P][f]

[1]

( Po )

Where:

Vt = Minimum volume of expansion tank, gallons. Vs = Volume of system, not including expansion tank, gallons.

t = Average operating temperature, °F.

Pa = Atmospheric pressure, pounds per square inch. Pf = Fill pressure, pounds per square inch. Po = Maximum operating pressure, pounds per square inch.

For SI units: 1 gallon = 3.785 L

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BOILERS AND PRESSURE VESSELS

TABLE 1004.4(1) EXPANSION TANK CAPACITIES FOR GRAVITY HOT WATER SYSTEMS [1]
CMC § 1214.4.2 Medium relevance — show source text
1214.4.2 Nonpotable Makeup Fluid. Makeup fluid systems that are designed to add pre-mixed antifreeze solutions shall be permitted. Such systems shall include, but not be limited to, glycol feeders and limited-volume reservoir systems. On systems using additives, such as glycol or corrosion inhibitors, the use of a system pressurization unit or glycol feeder shall be required. 1214.5 Differential Pressure Regulation. Provisions shall be made to bypass zone flows in excess of design velocity in a multi-zone hydronic system where the closing of some or all of the two-way zone valves causes excess flow through the open zones or deadheading of a fixed-speed circulator or

pump. 1214.5.1 Differential Pressure Bypass Valve. Where a differential pressure bypass valve is used for the purpose specified in Section 1214.5, it shall be installed and adjusted to provide bypass of the distribution system when most or all of the zones are closed.

1214.6 Air-Removal Device. Provision shall be made for the removal of air from fluid in hydronic systems. Airremoval devices shall be located in the areas of the hydronic piping system where air is likely to accumulate. Air-removal devices shall be installed to facilitate their removal for examination, repair, or replacement. 1214.7 Air-Separation Device. To assist with the removal of entrained air, an air-separation device shall be installed in hydronic systems. The device shall be located in accordance with the manufacturer’s installation instructions or at the point of no mechanically-induced pressure change within the hydronic system. 1214.8 Secondary Loops. Secondary loops that are isolated from the primary heat-distribution loop by a heat exchanger are closed-loop hydronic systems and shall have an expansion tank in accordance with Section 1209.0, an airremoval device in accordance with Section 1214.6, and an air-separation device in accordance with Section 1214.7.

1215.0 Hydronic Space Heating. 1215.1 General. Based on the system design, the heat-distribution units shall be selected in accordance with the manufacturer’s specifications.

1215.2 Installation. Heat-distribution units shall be

installed in accordance with the manufacturer’s installation

instructions and this code.

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HYDRONICS

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1215.3 Balancing. System loops shall be installed so that the design flow rates are achieved within the system. 1215.4 Heat Transfer Fluid. The ignitable flash point of heat transfer fluid in a hydronic piping system shall be a minimum of 50°F (28°C) above the maximum system operating temperature. The heat transfer fluid shall be compatible with the makeup fluid supplied to the system.

1216.0 Steam Systems.

1216.1 Steam Traps. For other than one-pipe steam systems, each heat-distribution unit shall be supplied with a steam trap that is listed for the application.

1216.2 Sloping for Two-Pipe System. Two-pipe steam system piping and heat-distribution units shall be sloped down at not less than [ 1] / 8 inch per foot (10.4 mm/m) in the direction of the steam flow.
CMC § 1210.3 Medium relevance — show source text
1210.3 Hangers and Supports. Pipe and tubing shall be supported in accordance with Section 313.0. Equipment that is part of the piping system shall be provided with additional support in accordance with this code and manufacturer’s installation instructions. Radiant systems utilizing heat emission or transfer plates shall have a gap of at least ¼ inch (6.4 mm) between adjacent plates. 1210.4 Oxygen Diffusion Corrosion. PEX and PE-RT tubing in closed hydronic systems shall contain an oxygen barrier. 1210.4.1 Vented Closed-Loop Systems. All components installed in a vented closed-loop system shall be constructed of non-ferrous or other corrosion resistant

materials.

1210.4.2 Non-Oxygen Barrier Closed-Loop Sys- tems. All components installed in a non-oxygen barrier system shall be constructed of non-ferrous or other corrosion resistant materials.

1211.0 Joints and Connections.

1211.1 General. Joints and connections shall be of an approved type. Joints shall be gas and watertight and designed for the pressure of the hydronic system. Changes in direction shall be made by the use of fittings or with pipe bends. Joints between pipe and fittings shall be installed in accordance with the manufacturer’s installation instructions. Joints used underground shall be of an approved type for buried applications in accordance with Section 1221.2.3.

1211.2 Pipe Bends. Pipe bends shall be formed in accordance with Section 1211.2.1 for PEX or Section 1211.2.2 for

PE.

1211.2.1 Crosslinked Polyethylene (PEX) Tubing. Crosslinked polyethylene (PEX) tubing bends shall have a bend radius of not less than eight times the outside diameter of the tubing or shall be in accordance with the manufacturer’s installation instructions.

1211.2.2 Polyethylene (PE) Plastic Pipe/Tubing. Polyethylene pipe and tubing bends shall have a bend radius in accordance with Table 1211.2.2. When a fitting or flange connection is present in the pipe bend, the minimum bend radius shall be one hundred times the pipe outside diameter (OD) for a distance of five times the pipe diameter on either side of the fitting location.

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1208.2 Mounting. The circulator or pump shall be installed in such a way that strain from the piping is not transferred to the circulator or pump housing. The circulator or pump shall be permitted to be directly connected to the piping, provided the piping is supported on each side of the circulator or pump. Where the installation of a circulator or pump will cause strain on the piping, the circulator or pump shall be installed on a mounting bracket or base plate or securely fastened to or supported by the structure with approved fastening devices. Where means for controlling vibration of a circulator or pump is required, an approved means for support and restraint shall be provided. 1208.3 Sizing. The selection and sizing of a circulator or pump shall be based on all of the following: (1) Loop or system head pressure, feet of head (m) (2) Capacity, gallons per minute (L/s) (3) Maximum and minimum temperature, °F (°C) (4) Maximum working pressure, pounds per square inch (kPa) (5) Fluid type

1209.0 Expansion Tanks. **1209.1 General.

CMC § 93.3 Medium relevance — show source text

A-93.3

Publication Date: 10/20/2021 Effective Date: 01/01/2022 Rev. 9c

Purpose and Scope

This gas design standard (GDS) provides specifications and design information for selecting and installing polyethylene (PE) and steel excess flow valves (EFVs).

1 General Information

1.1. EFVs are manufactured in accordance with American Society for Testing and Materials (ASTM International) F2138, “Standard Specification for Excess Flow Valves for Natural Gas Service,” and ASTM F1802, “Standard Test Method for Performance Testing of Excess Flow Valves.”

1.2. Only personnel qualified as described in GDS D-34, “Qualifications for Joining Polyethylene Pipe,” may install a plastic EFV.

1.3. Only personnel qualified as described in applicable welding procedures may install a steel EFV.

1.4. See Appendix C for an EFV installation and replacement matrix.

1.5. Exceptions to the guidelines listed in this GDS may be granted by Standards Engineering.

2 Applications for EFVs

2.1. Table 1 describes when EFVs must be installed on new, replaced, repaired, altered, and transferred service lines, except as noted in Step 2.2.

A. In certain scenarios an EFV is required only when there is a new complete service line or new stub service. This does not include repairs, alterations, replacements, or stub completions. It is recommended to install an EFV on existing or replaced services or stub completions, where practical (e.g., installing an EFV would not require upsizing the existing service).

Table 1. Required EFV Scenarios

Service Type	Total Connected Load in Standard Cubic Feet per Hour (scfh)	Col3
Service Type	0–1400	1401–5000
Single or branched service to single-family residence(s)1	EFV required	EFV required
Single or branched service to multifamily building(s)1	EFV required	EFV required for new service line2
Branched service to single-family residence and multifamily building1	EFV required	EFV required for new service line2
Single service to single commercial meter	EFV required	EFV required for new service line2
Any other service line (single or branched)	EFV required for new service line2	EFV required for new service line2

Step 6.2, “Branched Service Lines” describes appropriate EFV locations on branches.
Step 2.1.A provides an explanation on what is a new service line.

Printed copies of this document might be out of date. The Technical Information Library (TIL) has the current version.

PG&E Internal Information “PG&E” refers to Pacific Gas and Electric Company, a subsidiary of PG&E Corporation.

Page 1 of 19

Excess Flow Valves A-93.3

Publication Date: 10/20/2021 Effective Date: 01/01/2022 Rev. 9c

2.2. An EFV is not required in the following situations:

Frequently asked questions

Why does the code require the tank to be “closed-type”?

A closed-type tank holds the system fluid and a sealed air cushion (or diaphragm) so expansion raises system pressure rather than overflowing; § 1209.1 requires closed-type tanks for closed hydronic systems to control pressure caused by thermal expansion .

Can I isolate the expansion tank with a shutoff valve for servicing?

You may have a shutoff device, but the code requires it remain open during operation; handles must be locked open or removed to prevent accidental isolation (see § 1209.2) .

What if the system design pressure is over 30 psi?

If the system operates at more than 30 psi, the expansion tank must comply with ASME BPVC Section VIII.1 (see § 1209.3) .

How do I find the exact minimum tank capacity required by code?

The CMC requires sizing per § 1004.4 (Chapter 10), which contains the official tables and equations for the minimum capacity of closed‑type tanks; consult those tables or the manufacturer’s sizing charts and the code for the final selection (see § 1209.4 and § 1004.4) .

What support design is required for the tank?

Supports must be capable of carrying twice the weight of the tank filled with water without putting strain on connecting piping (see § 1209.2) .

Are there special chill or freeze requirements?

Hot-water-heating systems that incorporate hot water tanks or fluid relief columns must be installed to prevent freezing under normal operating conditions (see § 1209.2) .

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