CMC · California Mechanical Code
Where must hydronic pressure-relief valves discharge?
If you have a closed hydronic heating system, its relief valve must vent full‑size and unobstructed by gravity through an air gap to a visible outside or drain location, with the pipe pointing down and the outlet between 6 inches and 2 feet above grade; the discharge pipe must not be trapped, threaded, isolated by valves, or directed into a water‑heater pan (see **§ 1206.1** and **§ 1206.2**) .
Last reviewed: July 6, 2026
What the code requires — 2-4 sentences
Closed hydronic systems must be protected by at least one pressure relief valve and that valve must be installed so the heat source cannot be isolated from a relief device (§ 1206.1) . The valve’s discharge piping must be full-size (not smaller than the valve outlet), have no shutoffs or obstructions, discharge by gravity through an air gap to drainage or outside, terminate pointing down and between 6 inches and 2 feet above grade, and be readily visible; additional material, freezing, and threading limits also apply (§ 1206.2) .
The most important rule: the relief must discharge full size, unobstructed, independently by gravity through an air gap to a visible point outside or to the drainage system, with the outlet pointing down and 6 in — 2 ft above the ground (§ 1206.2) .
Requirements in detail
General requirement (where a valve is required)
- Each closed hydronic system must have at least one pressure relief valve and each closed section that contains a heat source must have a relief valve located so the heat source cannot be isolated from the relief device (§ 1206.1) .
- Valves must be installed per their listing and manufacturer instructions (§ 1206.1) .
Discharge piping — mandatory features (from § 1206.2)
- No valves, obstructions, or means of isolation may be placed in the discharge piping.
- Size: discharge piping must be not less than the size of the valve outlet and must discharge full size to the flood level of the receiving area and pointing down.
- Materials must be rated for at least the operating temperature of the system or comply with ASME A112.4.1.
- The discharge must be independent, by gravity, through an air gap into a drainage system or outside the building.
- The outlet of the discharge pipe must terminate no less than 6 inches (152 mm) and no more than 2 feet (610 mm) above the ground, and must point downward.
- Discharge must not cause personal injury or structural damage.
- No portion of the discharge pipe may be trapped or subject to freezing.
- The terminal end of the pipe shall not be threaded.
- Discharge into a water heater pan is prohibited.
- The discharge termination point must be readily visible.
Decision-relevant dimensions and values (quick reference table)
| Issue / value | Required value or condition | Code Reference |
|---|---|---|
| Minimum discharge pipe size | Not smaller than valve outlet (full size) | § 1206.2(1) |
| Vertical termination above grade | ≥ 6 in (152 mm) and ≤ 2 ft (610 mm) | § 1206.2(3) |
| Direction of outlet | Pointing downwards | § 1206.2(1) and (3) |
| Isolation devices in discharge | Prohibited (no valves/obstructions) | § 1206.2 intro |
| Terminal end threading | Not permitted | § 1206.2(6) |
| Freeze exposure | No part trapped or subject to freezing | § 1206.2(5) |
| Discharge to water heater pan | Prohibited | § 1206.2(7) |
| Visibility | Termination point must be readily visible | § 1206.2(8) |
| Material temperature rating | Rated ≥ operating temperature or comply with ASME A112.4.1 | § 1206.2(2) |
Exceptions & special cases
- Section 1206.2 itself does not list exceptions for hydronic relief discharge — the requirements above are mandatory for hydronic systems under Chapter 12 (§ 1206.2) .
- Where discharge could be hazardous (steam, very hot discharge, or industrial boilers), Chapter 10 contains additional rules (for example, splash shields where operating temperature exceeds 212°F) — see § 1005.3 for splash-shield guidance and other boiler/pressure-vessel discharge rules (§ 1005.3) . Use those provisions when the hydronic equipment is also a boiler or pressure vessel falling under Chapter 10.
Common mistakes
- Installing a shutoff or isolation valve between the relief valve and its discharge (prohibited) — violates the “no valves or obstructions” rule (§ 1206.2) .
- Reducing the discharge pipe size downstream of the valve (must remain full size) (§ 1206.2(1)) .
- Threading the terminal end of the discharge pipe (terminal end shall not be threaded) (§ 1206.2(6)) .
- Routing the discharge to a pan or location that is not permitted (e.g., into a water heater pan) (§ 1206.2(7)) .
- Locating the terminal so it can freeze or becomes trapped (no trapped sections or freezing exposure) (§ 1206.2(5)) .
- Concealing or otherwise making the terminal not readily visible (termination must be readily visible) (§ 1206.2(8)) .
Worked example — concrete scenario
Scenario: A residential closed hydronic heating loop has a listed pressure‑relief valve with a 3/4‑inch outlet attached to the boiler. How must the discharge be installed?
- Pipe size: use discharge piping with inside diameter not less than 3/4 in (match the valve outlet) so it discharges full size to the flood level of the receiving area (§ 1206.2(1)) .
- Routing: run the discharge independently (no shutoffs or traps) and slope/route by gravity to an exterior termination or a floor drain via an air gap as required (§ 1206.2(3)) .
- Termination: terminate the pipe pointing down with the end between 6 in (152 mm) and 24 in (610 mm) above ground or measurable floor level, and leave the end unthreaded so nothing can be attached (§ 1206.2(3) and (6)) .
- Materials: choose piping material rated for the system temperature (for example, if the hydronic water temperature is ~180°F, use a material rated ≥ 180°F or approved per ASME A112.4.1) (§ 1206.2(2)) .
- Visibility & protection: place the terminal where it is readily visible, not subject to freezing, and where flow will not spray onto people or damage structure (§ 1206.2(4), (5), (8)) .
Related provisions (see these CMC sections)
- § 1206.1 — General requirement for pressure and safety devices in hydronics (each closed hydronic system requires at least one relief valve) .
- § 1206.2 — Discharge piping requirements for hydronic relief devices (main controlling text cited throughout) .
- § 1005.2 — General discharge piping rules for pressure/temperature relief valves on boilers and pressure vessels (similar sizing and blockage prohibition) — useful when the hydronic equipment also falls under Chapter 10 .
- § 1005.3 — Splash shield requirement where operating temperature exceeds 212°F (applies to very hot discharges) .
- See the code index under “Pressure-Relief Valve — Discharge” for cross‑references (index entries point to § 1005.2, § 1112.10, § 1112.11, § 1206.2) .
Code references
Grounded in the retrieved California Mechanical Code — click a citation to read the verbatim passage:
CMC § 501.8 High relevance — show source text
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APPENDIX F
allow the fire department’s mobile air unit to connect and augment the system with a constant source of breathing air. Each fire department connection panel shall contain not less than two inlet air connections.
F 501.8 Pressure-Relief Valve. Pressure-relief valves shall be installed downstream of the pressure regulator inlet. The relief valve shall meet the requirements of CGA S-1.3 and shall not be field adjustable. The relief valve shall have a setto-open pressure not exceeding 1.1 times the design pressure of the system. Pressure-relief valve discharge shall terminate so that the exhaust air stream cannot impinge upon personnel in the area. Valves, plugs, or caps shall not be installed in the discharge of a pressure-relief valve. Where discharge piping is used, the end shall not be threaded.
F 501.9 Security. The fire department connection panel enclosure shall be locked by an approved means.
F 601.0 Interior Cylinder Fill Panels. F 601.1 Cabinet Requirements. Each cylinder fill panel shall be installed in a metal cabinet constructed of not less than 18-gauge carbon steel or equivalent. The depth of the cabinet shall not create an exit obstruction where installed in building stairwells. Except for the shutoff valve, pressure gauges, fill hoses and ancillary components; no system components shall be visible and shall be contained behind a not less than an 18-gauge interior panel. F 601.2 Clearance and Access. The panel shall be located not less than 36 inches (914 mm) but not more than 60 inches (1524 mm) above the finished floor or a stairway landing. Clear, unobstructed access shall be provided to each panel.
F 601.3 Door. The door shall be arranged such that where the door is open, it does not reduce the required exit width or create an obstruction in the path of egress. F 601.4 Cabinet Marking. The front of each cylinder fill panel shall be marked, “FIREFIGHTER AIR SYSTEM.” The lettering shall be in a color that contrasts with the cabinet front and in letters that are not less than 2 inches (51 mm) high with a [3] ⁄ 8 of an inch (9.5 mm) brush stroke. F 601.5 Cabinet Components. The cabinet shall be of a size to allow for the installation of the components in Section F 601.5.1.
F 601.5.1 Cylinder Fill Panel. The cylinder fill panel shall contain the gauges, isolation valves, pressure-relief valves, pressure-regulating valves, check valves, tubing, fittings, supports, connectors, hoses, adapters, and other components to refill SCBA cylinders. F 601.6 Cylinder Filling Hose. The design of the cabinet shall provide a means for storing the hose to prevent kinking. Where the hose is coiled, the brackets shall be installed so that the hose bend radius is maintained at 4 inches (102 mm) or greater. Fill hose connectors for connection to SCBA cylinders shall comply with the requirements of CGA V-1, number 346 or 347. No other SCBA cylinder fill connections shall be permitted. F 601.7 Security. Each panel cover shall be maintained and locked by an approved means.
CMC § 3.785 High relevance — show source text
INSTALLED EQUIVALENT
DIRECT RADIATION2
(square feet)TANK CAPACITY
(gallons)
Up to 35018
Up to 45021
Up to 65024
Up to 90030
Up to 110035
Up to 140040
Up to 16002 to 30
Up to 18002 to 30
Up to 20002 to 35
Up to 24002 to 40 For SI units: 1 gallon = 3.785 L, 1 square foot = 0.0929 m [2]
Notes: 1 Based on a two-pipe system with an average operating water temperature of 170°F (77°C), using cast-iron column radiation with a heat emission rate of 150 British thermal units per square foot hour [Btu/(ft [2] - h)] (473 W/m [2] ) equivalent direct radiation. 2 For systems that exceed 2400 square feet (222.9 m 2 ) of installed equivalent direct water radiation, the required capacity of the cushion tank shall be increased on the basis of 1 gallon (4 L) tank capacity per 33 square feet (3.1 m [2] ) of additional equivalent direct radiation.
TABLE 1004.4(2) EXPANSION TANK CAPACITIES FOR FORCED HOT WATER SYSTEMS [1]
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.
CMC § 8.2 High relevance — show source text
Exception: Outdoor systems containing Group A1 refrigerant shall be permitted to discharge at any elevation where the point of discharge is located in an access-controlled area accessible to authorized personnel only.
(2) The point of vent discharge shall be located not less than 20 feet (6096 mm) from windows, building ventilation openings, pedestrian walkways, or building exits.
(3) For heavier-than-air refrigerants, the point of vent discharge shall be located not less than 20 feet (6096 mm) horizontally from below-grade walkways, entrances, pits, or ramps where a release of the entire system charge into such a space would yield a concentration of refrigerant in excess of the RCL. The direct discharge of a relief vent into enclosed outdoor spaces, such as a courtyard with walls on all sides, shall not be permitted where a release of the entire system charge into such a space would yield a concentration of refrigerant in excess of the RCL. The volume for the refrigerant concentration calculation shall be determined using the gross area of the space and a height of 8.2 feet (2499 mm), regardless of the actual height of the enclosed space.
(4) The termination point of a vent discharge line shall be made in a manner that prevents discharged refrigerant from spraying directly onto personnel that are capable of being in the vicinity.
(5) The termination point of vent discharge lines shall be made in a manner that prevents foreign material or debris from entering the discharge piping.
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(6) Relief vent lines that terminate vertically upward and are subject to moisture entry shall be provided with a drip pocket having a length of not less than 24 inches (610 mm) and having the size of the vent discharge pipe. The drip pocket shall be installed to extend below the first change in vent pipe direction and shall be fitted with a valve or drain plug to permit removal of accumulated moisture. [ASHRAE 15:9.7.8.2]
1112.11.3 Internal Relief. Pressure-relief valves
designed to discharge from a higher-pressure vessel into a lower pressure vessel internal to the system shall comply with the following:
(1) The pressure-relief valve that protects the higherpressure vessel shall be selected to deliver capacity in accordance with Section 1113.5 without exceed ing the maximum allowable working pressure of the higher-pressure vessel accounting for the change in mass flow capacity due to the elevated backpressure.
(2) The capacity of the pressure-relief valve protecting the part of the system receiving a discharge from a pressure-relief valve protecting a higher-pressure vessel shall be not less than the sum of the capacity required in Section 1113.5 plus the mass flow capacity of the pressure-relief valve discharging into that part of the system.
(3) The design pressure of the body of the relief valve used on the higher-pressure vessel shall be rated for operation at the design pressure of the higher-pressure vessel in both pressure-containing areas of the valve. [ASHRAE 15:9.7.8.3]
1112.11.4 Discharge Location, Special Require- ments. Additional requirements for pressure relief device discharge location and allowances shall apply for specific refrigerants in accordance with Section 1112.11.4.1. [ASHRAE 15:9.7.8.4]
CMC § 302.5 High relevance — show source text
water service outlet. Where a hose bibb or outlet is installed on the supply outlet riser in addition to the service connector, a listed backflow preventer shall be installed on each additional outlet.
E 302.5 Pressure-Relief Valve. Where it is required to install a backflow preventer at the manufactured home lot service outlet, a listed pressure-relief valve shall be installed in the water service line on the discharge side of the backflow preventer. Pressure-relief valves shall be set to release at a pressure at a maximum of 150 psi (1034 kPa). Pressurerelief valves shall discharge toward the ground. Backflow preventers and pressure-relief valves shall be not less than 12 inches (305 mm) above the ground.
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APPENDIX E
E 302.6 Mechanical Protection. Park water service out lets, backflow preventers, and pressure-relief valves shall be protected from damage by vehicles or other causes. Such protection shall be permitted to consist of posts, fencing, or other permanent barriers.
E 302.7 Water-Conditioning Equipment. A permit shall be obtained from the Authority Having Jurisdiction before installing water-conditioning equipment on a manufactured home lot. Approval of the park operator is required on applications for a permit to install such equipment. Where the water-conditioning equipment is of the regenerating type, and the park drainage system discharges into a public sewer, approval of the sanitary district or agency having jurisdiction over the public sewer is required.
E 302.7.1 Approval. Regenerating water-conditioning equipment shall be listed and labeled by an approved listing agency.
E 302.7.2 Installation. Regenerating units shall discharge the effluent of regeneration into a trap not less than 1 [1] ⁄ 2 inches (40 mm) in diameter connected to the manufactured home park drainage system. An approved air gap shall be installed on the discharge line a minimum of 12 inches (305 mm) above the ground.
E 302.8 Testing. Installations shall be tested and inspected in accordance with Chapter 3 of this code.
E 401.0 Fuel Supply.
E 401.1 Fuel Gas Piping Systems. All fuel gas piping systems serving manufactured homes, accessory buildings, or structures and communities shall be designed and constructed in accordance with any applicable provisions of NFPA 54 and NFPA 58. NFPA 31 shall apply to oil fuel-burning systems and shall conform to the criteria of the Authority Having Jurisdiction. [NFPA 501A:4.1.1.1 – 4.1.1.2]
E 401.2 Gas Supply Connections. Gas supply connections at sites, where provided from an underground gas supply piping system, shall be located and arranged to permit attachment to a manufactured home occupying the site.
For the installation of liquefied petroleum gas (LP-Gas) storage systems, the provisions of NFPA 58 shall be followed. [NFPA 501A:4.1.2.1 – 4.1.2.2]
E 401.3 Location of Gas Supply Connection. The gas supply to the manufactured home shall be located within 4 feet (1219 mm) of the manufactured home stand.
CMC § 1112.11.3 High relevance — show source text
1112.11.3 Internal Relief. Pressure-relief valves
designed to discharge from a higher-pressure vessel into a lower pressure vessel internal to the system shall comply with the following:
(1) The pressure-relief valve that protects the higherpressure vessel shall be selected to deliver capacity in accordance with Section 1113.5 without exceed ing the maximum allowable working pressure of the higher-pressure vessel accounting for the change in mass flow capacity due to the elevated backpressure.
(2) The capacity of the pressure-relief valve protecting the part of the system receiving a discharge from a pressure-relief valve protecting a higher-pressure vessel shall be not less than the sum of the capacity required in Section 1113.5 plus the mass flow capacity of the pressure-relief valve discharging into that part of the system.
(3) The design pressure of the body of the relief valve used on the higher-pressure vessel shall be rated for operation at the design pressure of the higher-pressure vessel in both pressure-containing areas of the valve. [ASHRAE 15:9.7.8.3]
1112.11.4 Discharge Location, Special Require- ments. Additional requirements for pressure relief device discharge location and allowances shall apply for specific refrigerants in accordance with Section 1112.11.4.1. [ASHRAE 15:9.7.8.4]
1112.11.4.1 Water (R-718). Where water is the only refrigerant, discharge to a floor drain shall be permitted where all of the following conditions are
met:
(1) The pressure-relief device set pressure shall not exceed 15 psig (103 kPag).
(2) The floor drain shall be sized to handle the flow rate from a single broken tube in any refrigerantcontaining heat exchanger.
(3) Either of the following:
(a) The Authority Having Jurisdiction finds it acceptable that the working fluid, corrosion inhibitor, and other additives used in this type of refrigeration system are permitted to infrequently be discharged to the sewer system, or
(b) A catch tank sized to handle the expected discharge shall be installed and equipped
For SI units: 1 foot = 304.8 mm, 1 pound-force per square inch =
6.8947 kPa, 1 pound per minute = 0.00756 kg/s
with a normally closed drain valve and an overflow line to drain. [ASHRAE 15:9.7.8.4.1]
1112.12 Discharge Piping. The piping used for pressure-relief device discharge shall be in accordance with Section 1112.12.1 through Section 1112.12.5. [ASHRAE 15:9.7.9]
1112.12.1 Piping Connection. Piping connected to the discharge side of a fusible plug or rupture member shall have provisions to prevent plugging of the pipe upon operation of a fusible plug or rupture member.
[ASHRAE 15:9.7.9.1]
1112.12.2 Pipe Size. The size of the discharge pipe from the pressure-relief device or fusible plug shall be not less than the outlet size of the pressure-relief device or fusible plug. [ASHRAE 15:9.7.9.2]
CMC § 1307.3 High relevance — show source text
ways.
(3) Medical device applications directly related to respiration.
(4) Power for medical devices used directly on patients.
(5) Calibration of medical devices intended for Section 1307.3(1) through Section 1307.3(4).
(6) Simulation centers for the education, training, and assessment of health care professionals. [NFPA 99:5.1.3.5.2]
1307.4 Materials. Materials used in central supply systems shall meet the following requirements:
(1) In those portions of systems intended to handle oxygen at gauge pressures greater than 350 pounds-force per square inch (psi) (2413 kPa), interconnecting hose shall contain no polymeric materials.
(2) In those portions of systems intended to handle oxygen or nitrous oxide material, construction shall be compatible with oxygen under the temperatures and pressures to which the components can be exposed in the containment and use of oxygen, nitrous oxide, mixtures of these gases, or mixtures containing more than 23.5 percent oxygen.
(3) If potentially exposed to cryogenic temperatures, materials shall be designed for low temperature service.
(4) If intended for outdoor installation, materials shall be installed per the manufacturer’s requirements. [NFPA 99:5.1.3.5.4]
1308.0 Pressure-Regulating Equipment.
1308.1 Where Required. Pressure-regulating equipment shall be installed in the supply main upstream of the final linepressure valve. Where multiple piping systems for the same gas at different operating pressures are required, separate pressure-regulating equipment, relief valves, and source shutoff valves shall be provided for each pressure.
1308.2 Pressure Relief Valves. All pressure relief valves shall meet the following requirements:
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HEALTH CARE FACILITIES AND MEDICAL GAS AND MEDICAL VACUUM SYSTEMS
(1) They shall be of brass, bronze, or stainless steel construction.
(2) They shall be designed for the specific gas service.
(3) They shall have a relief pressure setting not higher than the maximum allowable working pressure (MAWP) of the component with the lowest working pressure rating in the portion of the system being protected.
(4) They shall be vented to the outside of the building, except that relief valves for compressed air systems having less than 3000 cubic feet (84 950 L) at STP shall be permitted to be diffused locally by means that will not restrict the flow.
(5) They shall have a vent discharge line that is not smaller than the size of the relief valve outlet or ¾ NPS (20 mm), whichever is larger.
(6) Where two or more relief valves discharge into a common vent line, the internal cross-sectional area of the common line shall be not less than the aggregate cross-sectional area of all relief valve vent discharge lines served.
(7) They shall not discharge into locations creating potential hazards.
(8) They shall have the discharge terminal turned down and screened to prevent the entry of rain, snow, or vermin.
(9) They shall be designed in accordance with ASME B31.3.
[NFPA 99:5.1.3.5.6.1]
CMC § 1204.8 High relevance — show source text
1204.8 Identification of Chemical Additives. In systems where chemical additives are used, documentation including the following information shall be readily accessible and maintained onsite:
(1) Concentrations
(2) Maintenance requirements
(3) Maintenance log
(4) Material Safety Data Sheet (SDS)
For SI units: 1000 British thermal units per hour = 0.293 kW
1205.0 Installation, Testing, and Inspection.
1205.1 Operating Instructions. Operating and maintenance information shall be provided to the building owner. 1205.2 Pressure Testing. System piping and components shall be tested with a pressure of not less than one and one-half times the operating pressure but not less than 100 psi (689 kPa). Piping shall be tested with water or air except that plastic pipe
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HYDRONICS
shall not be tested with air. Test pressures shall be held for a period of not less than 30 minutes with no perceptible drop in pressure. These tests shall be made in the presence of the Authority Having Jurisdiction.
Exceptions: (1) For PEX, PP-R, PP-RCT, PEX-AL-PEX, PE-RT, and PEAL-PE piping systems, testing with air shall be permitted where authorized by the manufacturer’s instructions for the PEX, PP-R, PP-RCT, PEX-AL-PEX, PE-RT, and PE-ALPE pipe and fittings products, and air testing is not prohibited by applicable codes, laws, or regulations outside this code.
Note: [HCD 1 & HCD 2] PEX-AL-PEX is not adopted in the California Plumbing Code for use in potable water supply and distribution systems. (2) Copper tubing shall be tested at not less than 80 psi (552 kPa). 1205.3 Flushing. Heating and cooling sources, system piping and tubing shall be flushed after installation with water or a cleaning solution. Cleaning and flushing of the heating and cooling sources shall comply with the manufacturer’s instructions. The cleaning solution shall be compatible with all system components and shall be used in accordance with the manufacturer’s instructions.
1206.0 Pressure and Safety Devices. 1206.1 General. Each closed hydronic system shall be protected against pressures exceeding design limitations with not less than one pressure relief valve. Each closed section of the system containing a heat source shall have a relief valve located so that the heat source is not capable of being isolated from a relief device. Pressure relief valves shall be installed in accordance with their listing and the manufacturer’s installation instructions.
1206.2 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 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.
CMC § 304.8 High 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.
CMC § 1112.12.4 Medium relevance — show source text
1112.12.4 Design Back Pressure. The design back pressure due to flow in the discharge piping at the outlet of pressure relief devices and fusible plugs, discharging to atmosphere, shall be limited by the allowable equivalent length of piping determined in accordance with Equation 1112.12.4(1).
[Equation 1112.12.4(1)]
L= 0.2146 - d [5] ( P [2] 0 P 22 ) d - ln
(P0P2 )f - C [2] r 6 - f
Where:
L = Equivalent length of discharge piping, feet.
Cr = Rated capacity as stamped on the pressure relief device in pounds per minute (lb/min), or in standard cubic feet per minute (SCFM) multiplied by 0.0764, or as calculated in Section 1112.14 for a rupture member or fusible plug, or as adjusted for reduced capacity due to piping in accordance with the manufacturer of the device, or as adjusted for reduced capacity due to piping as estimated by an approved method.
f = Moody friction factor in fully turbulent flow.
d = Inside diameter of pipe or tube, inches.
ln = Natural logarithm.
P2 = Absolute pressure at outlet of discharge piping, psia.
P0 = Allowed back pressure (absolute) at the outlet of pressure relief device, psia.
22 ) d - ln
(L=
0.2146 - d [5] ( P [2] 0 P
( P [2] 0 P 22 ) d - ln
(P0P2 )f - C [2] r 6 - f
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REFRIGERATION
expected to operate simultaneously, connect to a common discharge pipe, the common pipe shall be sized large enough to prevent the back pressure at each pressure-relief device from exceeding the maximum allowable back pressure in accordance with Section 1112.12.4.
[ASHRAE 15:9.7.9.3.3]
1112.13 Rating of Pressure-Relief Device. The rated discharge capacity of a pressure-relief device expressed in pounds of air per minute (kg/s), shall be determined in accordance with ASME BPVC Section VIII.1. Pipe and fittings between the pressure-relief valve and the parts of the system it protects shall have not less than the area of the pressurerelief valve inlet area. [ASHRAE 15:9.7.6]
1112.14 Rating of Rupture Members and Fusible Plugs. The rated discharge capacity of a rupture member or fusible plug discharging to the atmosphere under critical flow conditions, in pounds of air per minute (kg/s), shall be determined in accordance with the following formulas:
C = 0.64 P l d [2] [Equation 1112.14(1)]
CMC § 1205.3 Medium relevance — show source text
Note: [HCD 1 & HCD 2] PEX-AL-PEX is not adopted in the California Plumbing Code for use in potable water supply and distribution systems. (2) Copper tubing shall be tested at not less than 80 psi (552 kPa). 1205.3 Flushing. Heating and cooling sources, system piping and tubing shall be flushed after installation with water or a cleaning solution. Cleaning and flushing of the heating and cooling sources shall comply with the manufacturer’s instructions. The cleaning solution shall be compatible with all system components and shall be used in accordance with the manufacturer’s instructions.
1206.0 Pressure and Safety Devices. 1206.1 General. Each closed hydronic system shall be protected against pressures exceeding design limitations with not less than one pressure relief valve. Each closed section of the system containing a heat source shall have a relief valve located so that the heat source is not capable of being isolated from a relief device. Pressure relief valves shall be installed in accordance with their listing and the manufacturer’s installation instructions.
1206.2 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 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 (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 visible.
1207.0 Heating Appliances and Equipment. 1207.1 General. Heating appliances, equipment, safety and operational controls shall be listed for its intended use in a hydronic heating system and installed in accordance with the manufacturer’s installation instructions.
1207.2 Boilers. Boilers and their control systems shall comply with Section 1002.0. 1207.2.1 Condensing Boilers. A condensing boiler, in which the heat exchanger and venting system are designed to operate with condensing flue gases, shall be permitted to be connected directly to the panel heating system without a protective mixing device. 1207.2.2 Noncondensing Boilers. Where the heat exchanger and venting system are not designed to operate with condensed flue gases, the boiler shall be permitted to connect directly to the panel heating system where protected from flue gas condensation. The operating temperature of the boiler shall be more than the fluid temperature in accordance with the manufacturer’s instructions. The minimum return-water temperature to the heat source shall comply with Section 1201.5.
CMC § 1308.2 Medium relevance — show source text
1308.2 Pressure Relief Valves. All pressure relief valves shall meet the following requirements:
278 2025 CALIFORNIA PLUMBING CODE
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HEALTH CARE FACILITIES AND MEDICAL GAS AND MEDICAL VACUUM SYSTEMS
(1) They shall be of brass, bronze, or stainless steel construction.
(2) They shall be designed for the specific gas service.
(3) They shall have a relief pressure setting not higher than the maximum allowable working pressure (MAWP) of the component with the lowest working pressure rating in the portion of the system being protected.
(4) They shall be vented to the outside of the building, except that relief valves for compressed air systems having less than 3000 cubic feet (84 950 L) at STP shall be permitted to be diffused locally by means that will not restrict the flow.
(5) They shall have a vent discharge line that is not smaller than the size of the relief valve outlet or ¾ NPS (20 mm), whichever is larger.
(6) Where two or more relief valves discharge into a common vent line, the internal cross-sectional area of the common line shall be not less than the aggregate cross-sectional area of all relief valve vent discharge lines served.
(7) They shall not discharge into locations creating potential hazards.
(8) They shall have the discharge terminal turned down and screened to prevent the entry of rain, snow, or vermin.
(9) They shall be designed in accordance with ASME B31.3.
[NFPA 99:5.1.3.5.6.1]
1308.3 Pressure-Relief Valve Requirements. Central supply systems for positive pressure gases shall include one or more relief valves, all meeting the following requirements:
(1) They shall be located between each final line regulator and the source valve.
(2) They shall have a relief setting that is 50 percent above the normal system operating pressure, as indicated in Table 1305.1. [NFPA 99:5.1.3.5.6.4]
1309.0 Oxygen Concentrator Supply Units. 1309.1 Oxygen Requirements. Oxygen concentrator supply units for use with medical gas pipelines shall produce oxygen meeting the requirements of Oxygen 93 USP or Oxygen USP. [NFPA 99:5.1.3.9.1.1] 1309.2 Particulate Size. Output shall have less than or equal to 1.686 x 10 [-6] pounds per cubic yard (1 mg/m [3] ) of permanent particulates sized 1 micron or larger at normal atmospheric pressure. [NFPA 99:5.1.3.9.1.2] 1309.3 Suitability. Materials of construction on the air side of the oxygen concentrator unit shall be suitable for the service as determined by the manufacturer. [NFPA 99:5.1.3.9.1.3] 1309.4 Compatible Materials. Materials of construction on the oxygen side of the oxygen concentrator unit shall comply with Section 1307.4. [NFPA 99:5.1.3.9.1.4] 1309.5 Oxygen Concentrator Components. The components that make up the oxygen concentrator unit shall be as follows:
CMC § 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.
Frequently asked questions
Can I run the relief valve discharge into an underground storm drain?
No. The discharge must terminate by gravity through an air gap into the drainage system or outside the building with the end between 6 in and 2 ft above grade and pointing downward — underground or directly into a sealed drain would not meet the air‑gap/visibility and termination-height requirements (§ 1206.2(3)) .
Is it OK to cap the discharge during maintenance?
No. The code prohibits valves, obstructions, or any means of isolation in the discharge piping; the discharge must remain unobstructed at all times (§ 1206.2 ) .
Can the terminal be threaded so I can attach a flexible hose temporarily?
No. The terminal end shall not be threaded; the code explicitly forbids threaded end connections at the termination point (§ 1206.2(6)) .
What if my system discharges very hot water (over 212°F)?
If operating temperatures exceed 212°F, Chapter 10 addresses additional protection (splash shields or separators) for hot discharge. See § 1005.3 for splash‑shield guidance applicable to very hot discharges from safety devices .
Do these rules apply to every relief valve on a hydronic system?
Yes — each closed hydronic system must be protected and each closed section containing a heat source must have relief protection so the heat source cannot be isolated from the relief device (§ 1206.1) .
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