CPC · California Plumbing Code
What are the rules for TPR and vacuum relief devices?
TPR (temperature/pressure) and vacuum relief devices must be installed exactly per their listings and manufacturer instructions; you cannot put a shutoff between the valve and the heater; the relief valve’s discharge capacity must be at least the water heater’s input rating; non‑gas storage heaters additionally require an over‑temperature safety device and a combination T&P valve (CPC **§ 504.6** and **§ 505.2**).
Last reviewed: July 6, 2026
What the code requires — 2-4 sentences
The California Plumbing Code requires that temperature, pressure, and vacuum relief devices (and combinations) be installed per their listings and the manufacturer’s instructions — and that no shutoff valve be placed between the relief device and the water heater. The device’s discharge capacity (hourly Btu or rated steam relief capacity) must be not less than the input rating of the water heater, and discharge piping must be installed in accordance with the code. These core requirements are in § 504.6 and the related safety requirement for non‑gas storage heaters is in § 505.2.
The single most important rule: install TPR/vacuum relief devices exactly as listed and as the manufacturer requires; do not put a shutoff between the valve and the heater, and ensure the device can relieve at least the heater’s input rating. § 504.6.
Requirements in detail
Who needs what
- Temperature, pressure, and vacuum relief devices or acceptable combinations are required on water‑heating equipment; they must be installed per their listing and manufacturer instructions. § 504.6.
- For storage‑type water heaters and hot‑water boilers not fired by gas (for example, electric or oil), the code requires an over‑temperature safety device complying with nationally recognized standards and a combination temperature and pressure‑relief valve. § 505.2.
Installation controls and prohibitions
- No shutoff valve is allowed between the relief valve and the water heater, and no shutoff or isolating device is allowed on the discharge piping between the valve and the atmosphere. § 504.6.
- Relief devices must be installed in accordance with their listings and the manufacturer’s installation instructions. § 504.6.
Sizing and capacity
- The device’s hourly Btu (kW•h) discharge capacity or rated steam relief capacity must be not less than the input rating of the water heater — i.e., select a relief device whose relief capacity ≥ heater input. § 504.6.
Discharge piping
- Discharge piping for TPR/pressure devices must be installed per the discharge piping rules in the CPC (see discharge piping requirements). § 504.6 (refers discharge piping to Section 608.5).
- Section 608.5 contains the specific discharge piping requirements (full‑size to valve outlet, gravity discharge, air gap, terminal height, no traps, no threaded terminal, visible termination, etc.). § 608.5.
Table — decision‑relevant dimensions/values
| Decision factor | Requirement (plain English) | Code Reference |
|---|---|---|
| Device type required | Temperature, pressure, and/or vacuum relief device or combination installed per listing/manufacturer | § 504.6 |
| Prohibition on isolating valves | No shutoff valve between the relief valve and the water heater; no valve on discharge to atmosphere | § 504.6 |
| Minimum relief capacity | Device BTU/hr (or rated steam relief) ≥ water heater input rating | § 504.6 |
| Discharge piping | Discharge piping must meet discharge rules (full size, gravity air gap, 6"–2' terminal height, no traps, visible) | § 504.6 (discharge piping per § 608.5) |
| Non‑gas storage heaters | Must have over‑temperature safety device (to national standard) AND combination T&P relief valve | § 505.2 |
| Vacuum relief for elevated tanks | Install vacuum relief valve on storage tank or indirect heater located above fixture outlets (ANSI Z21.22/CSA 4.4) | § 608.7 (see related) |
Exceptions & special cases
- The CPC text for § 504.6 requires installation per listings and manufacturer instructions and does not provide alternate sizing rules — if a manufacturer’s listing or instructions specify particular sizing or installation methods, follow those as allowed by § 504.6.
- § 505.2 specifically targets storage‑type heaters and boilers deriving heat from fuels other than gas — these require the additional over‑temperature safety device and a combination T&P valve; the requirement is distinct from gas‑fired appliances. § 505.2.
- For vacuum relief specifics (when tank is located above fixtures), the CPC points to a standard (ANSI Z21.22/CSA 4.4) and includes the vacuum relief requirement in § 608.7; follow that standard where applicable. § 608.7.
If a specific technical detail you need (for example, how to compute required valve discharge area for a steam condition, or how to size multiple parallel relief devices) is not explicit in § 504.6 or § 505.2, the CPC either refers to the device listing/manufacturer or to other sections/standards. The code text retrieved here does not expand those computations in § 504.6 or § 505.2 beyond the capacity ≥ input rating requirement.
Common mistakes
- Installing a shutoff valve or isolation device between the relief device and the heater (violates § 504.6).
- Selecting a relief device with rated capacity less than the heater’s input rating (code requires device capacity ≥ input rating). § 504.6.
- Improper discharge piping: undersized outlet, trapped or frozen run, threaded terminal, or discharge not visible — discharge piping must follow the rules in § 608.5.
- For non‑gas storage heaters, omitting the required over‑temperature safety device or failing to install a combination T&P valve as required by § 505.2.
Worked example — concrete scenario
Scenario: You are installing a storage electric water heater with an input rating of 40,000 Btu/hr.
Step 1 — device selection: The T/P relief device chosen must have an hourly Btu (or rated steam) discharge capacity ≥ 40,000 Btu/hr. The code language in § 504.6 requires the device capacity not be less than the heater input rating.
Step 2 — installation location and valves: Do not install any shutoff valve between the relief valve and the water heater. § 504.6 prohibits a shutoff between the relief and the heater.
Step 3 — discharge piping: Install discharge piping per § 608.5: use pipe at least the size of the valve outlet, discharge by gravity through an air gap to the drain or outdoors, terminal not more than 2 ft and not less than 6 in above the ground (pointing down), no traps, terminal not threaded, and termination readily visible. (See § 608.5 for full list.)
Step 4 — documentation and listing: Install the relief device per its listing and the manufacturer’s instructions (mounting, orientation, piping). § 504.6 requires compliance with listings/manufacturer instructions.
If the heater were a non‑gas storage heater (e.g., oil‑fired), you would also provide the additional over‑temperature safety device and a combination temperature and pressure‑relief valve per § 505.2.
Related provisions
- § 504.6 — Temperature, Pressure, and Vacuum Relief Devices (core requirement).
- § 505.2 — Safety devices required for storage‑type water heaters and boilers not fired by gas (over‑temperature device + combination T&P).
- § 608.5 — Relief valve discharge piping requirements (size, air gap, terminal height, visibility, no traps).
- § 608.7 — Vacuum relief valves where storage tank/indirect heater is located above fixture outlets (standard ANSI Z21.22/CSA 4.4).
- § 504.4, § 504.5 — Related pressure‑ and temperature‑limiting device requirements referenced elsewhere in the water heater chapter.
Code references
Grounded in the retrieved California Plumbing Code — click a citation to read the verbatim passage:
CPC § 3.785 High relevance — show source text
For SI units: 1 gallon = 3.785 L
Notes: 1 The first-hour rating is found on the “Energy Guide” label. 2 Solar water heaters shall be sized to meet the appropriate first-hour rating as shown in the table.
2025 CALIFORNIA PLUMBING CODE 83
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WATER HEATERS
Exception: Where acceptable to the Authority Having Jurisdiction, gasketing of non-combustible or limitedcombustible material shall be permitted to be applied to the frame, provided closing and latching of the door are not inhibited.
504.2 Vent. Water heaters of other than the direct-vent type shall be located as close as practical to the chimney or gas vent. 504.3 Clearance. The clearance requirements for water heaters shall comply with Section 504.3.1 or Section 504.3.2.
504.3.1 Listed Water Heaters. The clearances shall not be such as to interfere with combustion air, draft hood clearance and relief, and accessibility for servicing. Listed water heaters shall be installed in accordance with their listings and the manufacturer’s installation instructions. 504.3.2 Unlisted Water Heaters. Except as otherwise permitted in this code, unlisted water heaters shall be approved by the Authority Having Jurisdiction prior to being installed. Clearance for unlisted water heaters shall be not less than 12 inches (305 mm) on all sides. Combustible floors under unlisted water heaters shall be protected in an approved manner. {NFPA 54-2018:10.27.2.2} 504.4 Pressure-Limiting Devices. A water heater installation shall be provided with overpressure protection using an approved, listed device installed in accordance with the terms of its listing and the manufacturer’s installation instructions. Pressure relief devices shall have a pressure setting greater than the water service pressure and not exceed 150 psi (1034 kPa) as required in Section 608.4. 504.5 Temperature Limiting Devices. A water heater installation or a hot water storage vessel installation shall be provided with overtemperature protection by means of an approved, listed device installed in accordance with the terms of its listing and the manufacturer’s installation instructions. {NFPA 54:10.26.5} 504.6 Temperature, Pressure, and Vacuum Relief Devices. Temperature, pressure, and vacuum relief devices or combinations thereof, and automatic gas shutoff devices shall be installed in accordance with the terms of their listings and the manufacturer’s installation instructions. A shutoff valve shall not be placed between the relief valve and the water heater or on discharge pipes between such valves and the atmosphere. The hourly British thermal units (Btu) (kW•h) discharge capacity or the rated steam relief capacity of the device shall be not less than the input rating of the water heater. {NFPA 54:10.26.6} Discharge piping shall be installed in accordance with Section 608.5.
504.7 Lead Content. Water heaters shall comply with the lead content requirements of Section 604.2.
CPC § 224.0 High relevance — show source text
Source . . . . . . . . . . . . . . . . . . . . .224.0, 1314.6, 1314.7,
1323.14.2, 1324.5.4.2
Temperature relief . . . . . . . . . . . . . .504.5, 504.6, 505.2
584 2025 CALIFORNIA PLUMBING CODE
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INDEX
Thermostatic . . . . . . . . . . . . . . . . . . . . . . .222.0, 408.4
Vacuum interface . . . . . . . . . . . . . . . . . . . . . . .C 501.2.4
Vacuum relief . . . . . . . . . . . .224.0, 504.6, 607.5, 608.7,
1505.11, 1506.10.3, 1602.9
Zone . . . . . . . . . . . . . . . . . . . . . . . . . . . . .224.0, 1314.4
VENT, PLUMBING . . . . . . . . . . . . . . . . . . . . . . . .Chapter 9
Below trap weir . . . . . . . . . . . . . . . . . . . . .905.5, 1002.4
Branch, definition . . . . . . . . . . . . . . . . . . . . . . . . .204.0
Buildings over 10 stories . . . . . . . . . . . . . . . . . . . .907.1 Changes in direction of . . . . . . . . . . . . . . . . . . . . .903.3
Chemical . . . . . . . . . . . . . . . . . . . . . .811.2, 811.5, 811.6
Combination waste and
vent system design . . . . . . . . . . . . . . . . .205.0, 910.0,
Appendix B
Connections . . . . . . . . . . . . .310.2, 805.0, Table 810.1,
905.1, 905.2, 908.1.2,
908.2.1, 911.2, 1503.2.2
Continuous, definition . . . . . . . . . . . . . . . . . . . . . .205.0
Definition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .224.0
Distance of trap from . . . . . . . . . . .1002.2, Table 1002.2
Double fitting for . . . . . . . . . . . . . . . . . . . . .704.2, 905.6
Engineered . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .912.0
Expansion joints . . . . . . . . . . .705.9.2, 1101.5, 1213.2.2
CPC § 54-2018 High relevance — show source text
Clearance for unlisted water heaters shall be not less than 12 inches (305 mm) on all sides. Combustible floors under unlisted water heaters shall be protected in an approved manner. {NFPA 54-2018:10.27.2.2} 504.4 Pressure-Limiting Devices. A water heater installation shall be provided with overpressure protection using an approved, listed device installed in accordance with the terms of its listing and the manufacturer’s installation instructions. Pressure relief devices shall have a pressure setting greater than the water service pressure and not exceed 150 psi (1034 kPa) as required in Section 608.4. 504.5 Temperature Limiting Devices. A water heater installation or a hot water storage vessel installation shall be provided with overtemperature protection by means of an approved, listed device installed in accordance with the terms of its listing and the manufacturer’s installation instructions. {NFPA 54:10.26.5} 504.6 Temperature, Pressure, and Vacuum Relief Devices. Temperature, pressure, and vacuum relief devices or combinations thereof, and automatic gas shutoff devices shall be installed in accordance with the terms of their listings and the manufacturer’s installation instructions. A shutoff valve shall not be placed between the relief valve and the water heater or on discharge pipes between such valves and the atmosphere. The hourly British thermal units (Btu) (kW•h) discharge capacity or the rated steam relief capacity of the device shall be not less than the input rating of the water heater. {NFPA 54:10.26.6} Discharge piping shall be installed in accordance with Section 608.5.
504.7 Lead Content. Water heaters shall comply with the lead content requirements of Section 604.2.
505.0 Oil-Burning and Other Water Heaters. 505.1 Water Heaters. Water heaters deriving heat from fuels or types of energy other than gas shall comply with the standards referenced in Table 501.1(1), Section 505.3, or Section 505.4. Vents or chimneys for such appliances shall be of approved types. An adequate supply of air for combustion and for adequate ventilation of heater rooms or compartments shall be provided. Each such appliance shall be installed in a
location approved by the Authority Having Jurisdiction and local and state fire-prevention agencies. 505.2 Safety Devices. Storage-type water heaters and hot water boilers deriving heat from fuels or types of energy other than gas, shall be provided with, in addition to the primary temperature controls, an over-temperature safety protection device that complies with and is installed in accordance with nationally recognized applicable standards for such devices and a combination temperature and pressure-relief valve.
505.3 Oil-Fired Water Heaters. Oil-fired water heaters
shall be installed in accordance with NFPA 31.
505.4 Indirect-Fired Water Heaters. Indirect-fired water heaters shall be in accordance with the applicable sections of the ASME Boiler and Pressure Vessel Code or shall comply with one of the other applicable standards shown in Table 501.1(1). Each water heater shall bear a label in accordance with ASME requirements, or an approved testing agency, certifying and attesting that such an appliance has been tested, inspected and meets the requirements of the applicable standards or code. 505.4.1 Single-Wall Heat Exchanger. An indirectfired water heater that incorporates a single-wall heat exchanger shall be in accordance with the following requirements:
CPC § 1112.14 High relevance — show source text
Where:
C = Rated discharge capacity expressed as mass flow of air, pounds per minute.
d = Smallest of the internal diameter of the inlet pipe, retaining flanges, fusible plug, and rupture member , inches.
For rupture members:
[Equation 1112.14(3)]
P1 = (rated pressure in psig x 1.1) + 14.7 psia
For fusible plugs:
P1 = Absolute saturation pressure corresponding to the stamped temperature melting point of the fusible plug or the critical pressure of the refrigerant used, whichever is smaller, pound-force per square inch atmosphere, psia. [ASHRAE 15:9.7.7]
For SI units:1 pound per minute = 0.00756 kg/s
1113.0 Overpressure Protection.
1113.1 General. Pressure vessels shall be provided with overpressure protection in accordance with ASME BPVC Section VIII.1. Pressure vessels containing liquid refrigerant that are capable of being isolated by stop valves from other parts of a refrigerating system shall be provided with overpressure protection. Pressure relief devices or fusible plugs shall be sized in accordance with Section 1113.5. [ASHRAE 15:9.7.1, 9.7.2]
»
Unless the maximum allowable back pressure ( P0 ) is specified by the relief valve manufacturer, the following maximum allowable back pressure values shall be used for P0, where P is the set pressure and Pa is atmospheric pressure at the nominal elevation of the installation (see Table 1112.12.4):
(1) For conventional relief valves: 15 percent of set
pressure:
P0 = (0.15• P )+ Pa [Equation 1112.12.4(2)] (2) For balanced relief valves: 25 percent of set pres sure:
P0 = (0.25• P )+ Pa [Equation 1112.12.4(3)]
(3) For rupture disks alone, fusible plugs, or pilot-operated relief devices: 50 percent of set pressure:
P0 = (0.50• P )+ Pa [Equation 1112.12.4(4)]
For fusible plugs, P shall be the saturated absolute pressure for the stamped temperature melting point of the fusible plug or the critical pressure of the refrigerant used, whichever is smaller. [ASHRAE 15:9.7.9.3.1, 9.7.9.3.2]
TABLE 1112.12.4
ATMOSPHERIC PRESSURE AT NOMINAL INSTALLATION ELEVATION ( Pa )
[ASHRAE 15: TABLE 9-2]
CPC § 1319.0 High relevance — show source text
(4) Vacuum receiver.
(5) Piping between the vacuum pump(s), discharge(s), receiver(s), and vacuum source shutoff valve in accordance with Section 1319.0, except brass, galvanized, or black steel pipe, which is permitted to be used as recommended by the manufacturer.
(6) Except as defined in Section 1312.2(1) through Section 1312.2(5), materials and devices used between the medical vacuum exhaust and the medical vacuum source that are permitted to be of any design or construction appropriate for the service as determined by the manufacturer.
(7) Vacuum filtration per Section 1312.4. [NFPA 99:5.1.3.7.1.1]
1312.3 Vacuum Receivers. Receivers for vacuum shall meet the following requirements:
(1) They shall be made of materials deemed suitable by the manufacturer.
(2) They shall comply with Section VIII.1, “Unfired Pressure Vessels,” of the ASME Boiler and Pressure Vessel Code.
(3) They shall be capable of withstanding a gauge pressure of 60 psi (414 kPa) and 30 inch (762 mm) gauge HgV.
(4) They shall be equipped with a manual drain.
(5) They shall be of a capacity based on the technology of the pumps. [NFPA 99:5.1.3.7.3]
1312.4 Vacuum Filtration. Central supply systems for vacuum other than liquid ring pumps shall be provided with inlet filtration with the following characteristics:
(1) Filtration shall be at least duplex to allow one filter to be exchanged without impairing the vacuum system.
(2) Filtration shall be located on the patient side of the vacuum producer.
(3) Filters shall be efficient to 0.3 µ and 99.97 percent HEPA or better, per DOE-STD-3020.
(4) Filtration shall be sized for 100 percent of the peak calculated demand while one filter or filter bundle is iso lated.
(5) It shall be permitted to group multiple filters into bundles to achieve the required capacities.
(6) The system shall be provided with isolation valves on the source side of each filter or filter bundle and isolation valves on the patient side of each filter or filter bundle, permitting the filters to be isolated without shutting off flow to the central supply system.
(7) A means shall be available to allow the user to observe any accumulations of liquids.
2025 CALIFORNIA PLUMBING CODE 281
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HEALTH CARE FACILITIES AND MEDICAL GAS AND MEDICAL VACUUM SYSTEMS
(8) A vacuum relief petcock shall be provided to allow vacuum to be relieved in the filter canister during filter replacement.
(9) Filter elements and canisters shall be permitted to be constructed of materials as deemed suitable by the manufacturer.
(10)In normal operation, one filter or filter bundle shall be isolated from the system to be available for service should a blockage in the operating filter occur or rotation of the filters be desired after filter element exchange.
[NFPA 99:5.1.3.7.4] 1312.5 Piping Arrangement and Redundancies. Piping arrangement shall be as follows:
(1) Piping shall be arranged to allow service and a continuous supply of medical-surgical vacuum in the event of a single fault failure.
CPC § 603.2 Medium relevance — show source text
Table 603.2, 603.3.2,
603.3.5, 603.3.6, 603.4.4,
603.5.1, 603.5.5, 603.5.6,
603.5.7, 603.5.9, 603.5.13,
603.5.15, 603.5.16, 1303.5,
C 501.3, E 505.4, E 506.1
VACUUM DRAINAGE SYSTEMS . . . . . . . . . . . . . . .C 501.0
VACUUM RELIEF VALVES . . . . . . . . . . . . . . . . .224.0, 504.6,
608.7, 1602.9
VACUUM SYSTEM –
LEVEL 1, DEFINITION . . . . . . . . . . . . . . . . . . . . . . .224.0
VALIDITY OF CODE . . . . . . . . . . . . . . . . . . . . . . . . . . .101.5
VALVES
Access door signs . . . . . . . . . . . . . . . . . . . . . .1505.8.2
Backwater . . . . . . . . . . . . . . . . . . . .204.0, 710.1, 710.3,
710.6, 1006.1, 1503.2.3,
1503.9.1, 1503.9.7,
1603.9, K 105.4
Balancing, definition . . . . . . . . . . . . . . . . . . . . . . .224.0
Ball . . . . . . . . . . . . . . . . . . . . . . . . .606.1, 606.4, 710.4,
710.6
Bathtub filler . . . . . . . . . . . . . . . . . . . . . . . . . . . . .409.5
Check . . . . . . . . . . . . . . . . . . . .603.5.10, 608.3, 710.4,
710.12.1, 710.13.2,
1004.2, 1208.11.1,
1309.11, 1311.5,
1313.5, F 701.3
Combination stop-and-waste . . . . . . . . . . . . . .603.5.17 Combination temperature
and pressure-relief . . . . . . . . . . . . . . . . .505.2, 608.3
Combination thermostatic/
pressure balancing . . . . . . . . . . . . . . . . .205.0, 408.4
Control . . . . . . . . . . . . . . . . . . . . . .408.10, 601.2, 606.5,
606.6, 1303.1, 1306.2,
C 501.3
Diaphragm-type . . . . . . . . . . . . . . . . . . .507.22, 1208.11
CPC § 3.785 Medium relevance — show source text
SYSTEM VOLUME2
(gallons)TANK CAPACITY
DIAPHRAGM TYPE
(gallons)TANK CAPACITY NON-
DIAPHRAGM TYPE
(gallons)
1009 15
20017 30
30025 45
40033 60
50042 75
100083 150
2000165 300 For SI units: 1 gallon = 3.785 L
Notes: 1 Based on an average operating water temperature of 195°F (91°C), a fill pressure of 12 psig (83 kPa), and an operating pressure of not more than 30 psig (207 kPa). 2 Includes volume of water in boiler, radiation, and piping, not including expansion tank.
1005.0 Safety or Relief Valve Discharge.
1005.1 General. Pressurized vessels or boilers shall be provided with overpressure protection by means of a listed pressure relief valve installed in accordance with the manufacturer’s
installation instructions.
1005.2 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 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 (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) Discharge to a termination point that is readily visible.
1005.3 Splash Shield. Where the operating temperature exceeds 212°F (100°C), the discharge pipe shall be installed with a splash shield or centrifugal separator.
1005.4 Hazardous Discharge. Where the discharge from safety valves is capable of being hazardous, discharge of steam inside the boiler room, such discharge shall be discharged to the outside of the boiler room. Discharges from relief valves on industrial boilers shall be discharged to an approved location.
1005.5 Vacuum Relief Valve. Hot-water heating systems that are subjected to a vacuum while in operation or during shutdown shall be protected with a vacuum relief valve that complies with ANSI Z21.22/CSA 4.4. Where the piping configuration, equipment location, and valve outlets are located below the boiler elevation, the system shall be equipped with a vacuum relief valve at the highest point.
1006.0 Shutoff Valves.
CPC § 304.8 Medium relevance — show source text
For SI units: 1 foot = 304.8 mm, 1 pound-force per square inch = 6.8947 kPa
1112.12.5 Simultaneous Operation. When outlets of two or more relief devices or fusible plugs, which are
TABLE 1112.12.4
ATMOSPHERIC PRESSURE AT NOMINAL INSTALLATION ELEVATION ( Pa )
[ASHRAE 15: TABLE 9-2]
For SI units: 1 foot = 304.8 mm, 1 pound-force per square inch = 6.8947 kPa
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REFRIGERATION
1113.2 Type of Protection. Pressure vessels with an internal gross volume of 3 cubic feet (0.1 m [3] ) or less shall use one or more pressure relief devices or a fusible plug. Pressure vessels of more than 3 cubic feet (0.1 m [3] ) but less than 10 cubic feet (0.28 m [3] ) internal gross volume shall use one or more pressure relief devices. Fusible plugs shall not be used.
[ASHRAE 15:9.7.2.1, 9.7.2.2]
1113.3 Discharging into Lowside of System. For pressure-relief valves discharging into the lowside of the system, a single relief valve (not rupture member) of the required relieving capacity shall not be used on vessels of 10 cubic feet (0.28 m [3] ) or more internal gross volume except under the conditions permitted in Section 1112.11.3. [ASHRAE 15:9.7.3]
1113.4 Parallel Pressure-Relief Devices. Two or more
pressure-relief devices in parallel to obtain the required capacity shall be considered as one pressure-relief device. The discharge capacity shall be the sum of the capacities required for each pressure vessel being protected.
1113.5 Discharge Capacity. The minimum required discharge capacity of the pressure-relief device or fusible plug for a pressure vessel shall be determined in accordance with ASHRAE 15.
1113.6 Three-Way Valve. Pressure vessels of 10 cubic feet (0.28 m [3] ) or more internal gross volume shall use one or more rupture member(s) or dual pressure-relief valves where discharging to the atmosphere. Dual pressure-relief valves shall be installed with a three-way valve to allow testing or repair. Where dual relief valves are used, the valve shall comply with Section 1113.5.
Exception: A single relief valve shall be permitted on pressure vessels of 10 cubic feet (0.28 m [3] ) or more internal gross volume where in accordance with the following conditions:
(1) The relief valves are located on the lowside of the sys tem.
(2) The vessel is provided with shutoff valves designed to allow pumpdown of the refrigerant charge of the pressure vessel.
(3) Other pressure vessels in the system are separately protected in accordance with Section 1113.1. [ASHRAE 15:9.7.2.3]
1114.0 Special Discharge Requirements.
CPC § 1005.3 Medium relevance — show source text
(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 (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) Discharge to a termination point that is readily visible.
1005.3 Splash Shield. Where the operating temperature exceeds 212°F (100°C), the discharge pipe shall be installed with a splash shield or centrifugal separator.
1005.4 Hazardous Discharge. Where the discharge from safety valves is capable of being hazardous, discharge of steam inside the boiler room, such discharge shall be discharged to the outside of the boiler room. Discharges from relief valves on industrial boilers shall be discharged to an approved location.
1005.5 Vacuum Relief Valve. Hot-water heating systems that are subjected to a vacuum while in operation or during shutdown shall be protected with a vacuum relief valve that complies with ANSI Z21.22/CSA 4.4. Where the piping configuration, equipment location, and valve outlets are located below the boiler elevation, the system shall be equipped with a vacuum relief valve at the highest point.
1006.0 Shutoff Valves.
1006.1 General. An approved manual shutoff valve shall be installed upstream of all control devices on the main burner of a gas-fired boiler. The takeoff point for the gas supply to the pilot shall be upstream of the gas shutoff valve of the main burner and shall be valved separately. A union or other approved means of disconnect shall be provided immediately downstream of these shutoff valves.
1007.0 Gas-Pressure Regulators.
1007.1 General. An approved gas-pressure regulator shall be installed on gas-fired boilers where the gas supply pressure is exceeding that at which the main burner is designed to operate. A separate approved gas-pressure regulator shall be installed to regulate the gas pressure to the pilot or pilots.
2025 CALIFORNIA MECHANICAL CODE 219
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BOILERS AND PRESSURE VESSELS
1008.0 Low-Water Cutoff.
1008.1 General. Hot water boilers and steam boilers shall be installed with a low-water cutoff. A coil-type boiler or a water-tube boiler that requires forced circulation to prevent overheating of the coils or tubes shall be installed with a flowsensing device in the outlet piping in lieu of the low-water cutoff. The low-water cutoff or the flow sensing device shall be installed so as to prevent damage to the boiler and to permit testing of the fuel-supply cutoff without draining the heating system. The low-water cutoff shall shut off the energy source at a water level setpoint that is in accordance with the boiler manufacturer’s instructions.
1009.0 Combustion Regulators – Safety Valves.
1009.1 General. The following requirements shall be retroactive:
CPC § 607.2 Medium relevance — show source text
607.2 Private Well Water Tanks . . . . . . .154
607.3 Potable Water Tanks . . . . . . . . . .154
607.4 Venting . . . . . . . . . . . . . . . . . . . . .154
607.5 Overflow . . . . . . . . . . . . . . . . . . . .154
607.6 Valves . . . . . . . . . . . . . . . . . . . . . .154
608.0 Water Pressure, Pressure Regulators, Pressure Relief Valves, and Vacuum Relief
Valves . . . . . . . . . . . . . . . . . . . . . .154
608.1 Inadequate Water Pressure . . . . .154
608.2 Excessive Water Pressure . . . . . .154
608.3 Expansion Tanks, and Combination Temperature and Pressure-Relief Valves . . . . .154
608.4 Pressure Relief Valves . . . . . . . . .154
608.5 Discharge Piping . . . . . . . . . . . . .154
608.6 Water-Heating Devices . . . . . . . . .155
608.7 Vacuum Relief Valves . . . . . . . . .155
609.0 Installation, Testing, Unions, and Location . . . . . . . . . . . . . . . . .155
609.1 Installation . . . . . . . . . . . . . . . . . .155
609.2 Trenches . . . . . . . . . . . . . . . . . . . .155
609.3 Under Concrete Slab . . . . . . . . . .155
609.4 Testing . . . . . . . . . . . . . . . . . . . . .155
609.5 Unions . . . . . . . . . . . . . . . . . . . . .155
609.6 Location . . . . . . . . . . . . . . . . . . . .155
609.7 Abutting Lot . . . . . . . . . . . . . . . . .155
609.8 Pumps . . . . . . . . . . . . . . . . . . . . .155
609.9 Low-Pressure Cutoff Required on Booster Pumps for Water Distribution Systems . . . . . . . . . . .156
2025 CALIFORNIA PLUMBING CODE xxxiii
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TABLE OF CONTENTS
609.10 Disinfection of Potable Water System . . . . . . . . . . . . . . . . . . . . .156
609.11 Water Hammer . . . . . . . . . . . . . . .156
609.12 Pipe Insulation . . . . . . . . . . . . . . .156
610.0 Size of Potable Water Piping . . . .156
610.1 Size . . . . . . . . . . . . . . . . . . . . . . . .156
610.2 Pressure Loss . . . . . . . . . . . . . . . .156
610.3 Quantity of Water . . . . . . . . . . . . .157
CPC § 505.0 Medium relevance — show source text
Oil-burning and other . . . . . . . . . . . . . . . . . . . . . .505.0 Permits required . . . . . . . . . . . . . . . . . . . . . . . . . .502.0
Pressure-relief valves . . . . . . . . . . .504.4, 504.6, 505.2,
608.2 – 608.5
Protection . . . . . . . . . . . . . . . . . . .504.3 – 504.6, 505.2,
507.2, 507.8, 507.10,
507.14.1, 507.24
Relief valve discharge . . . . . . . . . . . . . . . . . . . . . .608.5 Seismic provisions . . . . . . . . . . . . . . . . . . . . . . . . .507.2 Temperature and pressure-relief valves . . . . . . . . . . . . . . .504.6, 505.2 Temperature-limiting devices . . . . . . . . . . . . . . . . .504.5
Vents . . . . . . . . . . . . . . . . . . . . . . . . . . . . .509.0, 510.0
Water heating system requirements . . . . . . . . . . . .501.2 WATER SOFTENERS . . . . . . . . . . . . . . . . 611.4, Table 611.4
WATER STATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . .225.0
WATER TESTS
Building sewers . . . . . . . . . . . . . . . . . . . . . . . . . . .723.0 Drainage and vent systems . . . . . . . . . . . . .105.3, 712.2 Storm drainage . . . . . . . . . . . . . . . . . .1107.2.1, 1107.2.3 Water supply systems . . . . . . . .105.2.1.1, 105.3, 609.4
WATERPROOFING
AND WATERTIGHT
Building sewer . . . . . . . . . . . . . . . . . . . . . . . . . . . .723.1
Cleanouts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .707.3
Connections . . . . . . . . . . . . . . . . . . . . . . . . . . . . .105.3
Drain pans . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .507.5
Fixtures . . . . . . . . . . . . . . . . .402.2, 408.6, 408.8, 418.2
CPC § 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.
Frequently asked questions
When the code says “installed in accordance with the terms of their listings and the manufacturer’s installation instructions,” can I deviate if the local AHJ approves?
No. The CPC requires installation per the device listing and manufacturer instructions; deviations are only permitted if the Authority Having Jurisdiction (AHJ) explicitly approves an alternative. See § 504.6.
Can I put a ball valve on the TPR discharge pipe for testing or service?
No — § 504.6 expressly prohibits a shutoff valve between the relief valve and the water heater and on discharge piping to the atmosphere. Do not install isolation valves on that discharge.
How do I verify the relief device capacity is adequate?
Select a device whose hourly Btu (or rated steam relief) capacity is not less than the water heater’s input rating; this is the requirement in § 504.6. Manufacturer literature and listings normally state the device relieving capacity.
Does § 505.2 apply to gas‑fired storage heaters?
No. § 505.2 applies to storage‑type water heaters and hot‑water boilers deriving heat from fuels or energy types other than gas; it requires an over‑temperature safety device and a combination T&P valve for those appliances.
Where does the discharge pipe have to terminate?
Discharge piping must follow the discharge requirements referenced by the water‑heater sections — discharge independently by gravity through an air gap into the drainage system or outside, terminal between 6 in and 2 ft above grade, pointing down, visible, not trapped, and not threaded. See § 608.5.
More in California Plumbing Code
- Administration
- Definitions
- General Regulations
- Plumbing Fixtures and Fixture Fittings
- Water Heaters
- Water Supply and Distribution
- Sanitary Drainage (Drain, Waste, and Vent)
- Indirect Wastes
- Vents
- Traps and Interceptors
- Storm Drainage
- Fuel Gas Piping
- Health Care Facilities — Medical Gas and Medical Vacuum Systems
- Alternate Water Sources and Nonpotable Rainwater Catchment Systems
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