CMC · California Mechanical Code
Oxygen diffusion corrosion—requirements and mitigation
If your hydronic heating or cooling loop uses PEX or PE‑RT, the CMC requires tubing with an oxygen barrier. If the loop is vented or uses tubing that allows oxygen through, all pumps, valves and fittings in that oxygen‑exposed part of the loop must be non‑ferrous or corrosion‑resistant (see **§ 1210.4**, **§ 1210.4.1**, **§ 1210.4.2**).
Last reviewed: July 6, 2026
What the code requires — 2–4 sentences
The California Mechanical Code requires that PEX and PE‑RT tubing used in closed hydronic systems contain an oxygen barrier — § 1210.4. For systems that are vented closed‑loop systems or that are non‑oxygen barrier closed‑loop systems, the code requires that all components installed in those systems be constructed of non‑ferrous or other corrosion‑resistant materials — § 1210.4.1 and § 1210.4.2. These are the controlling CMC provisions for oxygen diffusion corrosion.
Use tubing with an oxygen barrier for closed hydronic systems, and where oxygen can enter the loop (vented or non‑barrier systems) use non‑ferrous or corrosion‑resistant components. § 1210.4 is the primary rule.
Requirements in detail
Scope and key defined terms (first appearance)
- Closed hydronic system — a looped water/heat‑transfer fluid system circulated by pumps (hydronics context is given in Chapter 12). See the hydronics definitions in the code.
- Oxygen barrier — a tubing construction or layer that prevents or greatly limits the diffusion of oxygen through plastic tubing (required for PEX and PE‑RT in closed hydronic systems). § 1210.4.
- Vented closed‑loop system — a closed loop that includes air/venting such that oxygen can enter the fluid; in these systems all components must be non‑ferrous or corrosion‑resistant. § 1210.4.1.
- Non‑oxygen barrier closed‑loop system — a system (or portion of a system) using piping/tubing that permits oxygen diffusion; in those systems all components must be non‑ferrous or corrosion‑resistant. § 1210.4.2.
Decision table — when to apply which requirement
| Decision dimension | Requirement | When it applies | Code Reference |
|---|---|---|---|
| Tubing material (PEX, PE‑RT) | Must include an oxygen barrier | Any closed hydronic system using PEX or PE‑RT | § 1210.4 |
| System is a vented closed‑loop system | All components must be non‑ferrous or corrosion‑resistant | When the loop is vented (oxygen ingress possible) | § 1210.4.1 |
| System uses non‑oxygen barrier tubing | All components must be non‑ferrous or corrosion‑resistant | When any portion of loop permits oxygen diffusion | § 1210.4.2 |
| Definition / identification | How the code treats “non‑oxygen barrier closed‑loop” | See hydronics definitions to classify systems | § 218.0 (definitions) and hydronics definitions |
Practical interpretation points (from the code text)
- The code text is prescriptive about the need for an oxygen barrier in PEX/PE‑RT tubing in closed hydronic loops (no performance standard or test method is specified in § 1210.4 itself).
- Where oxygen can enter the fluid (either because the loop is deliberately vented or because the tubing permits diffusion), the CMC requires non‑ferrous or corrosion‑resistant materials for all components in that part of the system. That applies to pumps, fittings, valves, heat exchangers, expansion tanks located on the oxygen‑exposed side, etc. § 1210.4.1 and § 1210.4.2.
Exceptions & special cases
- The text of § 1210.4, § 1210.4.1, and § 1210.4.2 does not list additional exceptions, alternate testing methods, or performance thresholds for what constitutes an acceptable oxygen barrier. The CMC statement is brief and mandatory in scope; any project‑specific exceptions would need to be approved by the Authority Having Jurisdiction (as allowed elsewhere in the code).
- The code does not, in § 1210.4, identify which brands or barrier constructions are acceptable, nor does it reference a specific ASTM/ISO test or maximum oxygen transmission rate. If you need an accepted performance standard you must rely on manufacturer listings, referenced standards, or AHJ approval (the CMC text here is silent on that detail).
- The definitions and hydronics chapter help classify whether a system is a non‑oxygen barrier closed‑loop system; use those definitions to determine which subsection applies.
Common mistakes
- Assuming any PEX/PE‑RT is compliant — some PEX/PE‑RT products are manufactured without an integrated oxygen barrier; the code requires an oxygen barrier for PEX/PE‑RT in closed hydronic systems (§ 1210.4). Always confirm product specification sheets.
- Installing ferrous pumps, valves, or fittings in a vented or non‑barrier loop — the code requires non‑ferrous or corrosion‑resistant components in those cases (§ 1210.4.1, § 1210.4.2).
- Confusing “closed” with “non‑oxygen barrier closed‑loop” — a closed loop can still be a non‑oxygen barrier closed‑loop if its piping permits oxygen diffusion; that triggers the non‑ferrous requirement. Check the hydronics definitions.
- Expecting the CMC to specify acceptable oxygen transmission rates or test standards in § 1210.4 — it does not. Do not substitute an assumed numeric threshold unless it’s documented by the product standard or AHJ.
Mitigation (industry practice) — what the code mandates vs what it does not
- What the CMC mandates: use oxygen‑barrier PEX/PE‑RT in closed hydronic systems and use non‑ferrous/corrosion‑resistant components in vented or non‑barrier systems (§ 1210.4, § 1210.4.1, § 1210.4.2).
- What the CMC does NOT specify in § 1210.4: specific oxygen transmission rate limits, acceptable barrier materials or test methods, or other operational mitigation (e.g., deaerators, oxygen scavengers, or glycol concentrations). These mitigation measures are common industry practice but are not prescribed by this section of the CMC. If you plan to rely on those methods, document them and obtain AHJ acceptance where required.
- Common industry mitigation measures (not specified by the cited CMC section) include: installing an inline air separator/deaerator, using closed‑cell expansion tanks or membrane expansion tanks, selecting stainless/bronze/brass components where oxygen exposure is possible, and specifying oxygen‑impermeable multilayer tubing (e.g., PEX‑AL‑PEX or barrier‑laminated PEX) where appropriate. Because these are not stated in § 1210.4, you should verify acceptance with the AHJ or rely on referenced product standards and manufacturer listings. (Code silence on these measures means they are acceptable only insofar as the AHJ and other referenced standards permit them.)
Worked example — concrete scenario
Scenario: A small commercial building hydronic heating loop uses PEX tubing, pumps, and an expansion tank. The installer must determine compliance.
- Is the loop a closed hydronic system using PEX? — Yes. Therefore the tubing must be oxygen‑barrier PEX. Action: specify and install PEX with an integrated oxygen barrier (per § 1210.4).
- Is the system vented (expansion tank open to atmosphere or air vents that allow oxygen ingress)? — If the expansion tank or any connection intentionally vents to atmosphere (a vented closed‑loop system), then all components in that vented loop must be non‑ferrous or corrosion‑resistant. Action: choose stainless, bronze, brass, or other corrosion‑resistant pumps, valves, and fittings (per § 1210.4.1).
- If you cannot provide oxygen‑barrier PEX for some portion of the loop (e.g., retrofit with existing non‑barrier PE piping), classify that part of the system as a non‑oxygen barrier closed‑loop system; you must install non‑ferrous/corrosion‑resistant components for that portion according to § 1210.4.2.
Notes: the CMC text does not tell you which oxygen barrier product is acceptable or give an OTTR (oxygen transmission) limit — that selection must be based on manufacturer data, referenced standards, and AHJ guidance.
Related provisions
- § 1210.1 — Piping, tubing, and fittings for hydronic systems (material lists and referenced standards).
- § 1210.2 — Expansion and contraction (installation considerations for hydronic tubing/pipe).
- § 1210.3 — Hangers and supports (support requirements for piping and tubing).
- § 1211.0 / § 1211.1 — Joints and connections (approved joint types and installation).
- § 218.0 — Definitions (used to classify hydronic system types such as “Non‑Oxygen Barrier Closed‑Loop”).
Code references
Grounded in the retrieved California Mechanical Code — click a citation to read the verbatim passage:
CMC § 1208.0 High relevance — show source text
1208.0 Circulators and Pumps. 1208.1 General. Circulators and pumps shall be selected for their intended use based on the heat transfer fluid, intended operating temperature range and pressure. Circulators and pumps shall be installed to allow for service and maintenance. The manufacturer’s installation instructions shall be followed for correct orientation and installation. Motor operated pumps rated 600V or less shall comply with CSA C22.2 No. 108 or UL 778.
2025 CALIFORNIA MECHANICAL CODE 259
), Copyright © 2025 IAPMO, and may not be used for any other purpose or distributed to any other persons or parties.
HYDRONICS
temperature and pressure of the system and shall be compatible with the type of heat transfer fluid. Pipe fittings and valves shall be approved for the specific installation with the piping, materials to be installed and shall comply with the applicable standards referenced in Table 1210.1. Where required, exterior piping shall be protected against freezing, UV radiation, corrosion and degradation. Embedded pipe or tubing shall comply with Section 1221.2. 1210.2 Expansion and Contraction. Pipe and tubing shall be so installed that it will not be subject to undue strains or stresses, and provisions shall be made for expansion, contraction, and structural settlement. [OSHPD 1, 1R, 2, 4 & 5] Pipe connections less than 2½ inches (64 mm) to heating coils, cool- ing coils, humidifiers, and similar equipment shall have flexible connectors or three (3) 90-degree offsets in close proximity of the connection.
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.
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 § 1308.4.4 Medium relevance — show source text
Fuel gas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1308.4.4, Table 1315.2(19)–Table 1315.2(23),
Table 1315.2(34)–Table 1315.2(36)
Hydronics . . . . . . . . . . . . . . . . . . . 1210.0, Table 1210.1
Joining and connections . . . . . . . . . . . . . . . . . . . . (see Joints
and connections)
POLYETHYLENE-ALUMINUM-POLYETHYLENE
(PE-AL-PE) PIPE OR TUBING
Definition. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 218.0
Ground source loop. . . . . . . Table 1703.2, Table 1703.3
Hydronics . . . . . . . . . . . . . . . . . . . 1210.0, Table 1210.1 Joining and connections. . . . . . . . . . . . . . . . (see Joints and connections)
POLYETHYLENE OF RAISED
TEMPERATURE (PE-RT) PIPE OR TUBING
Definition. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 218.0
Ground source loop . . . . . . . . . . . . . . . . . Table 1703.2,
Table 1703.3
Hydronics . . . . . . . . . . . . . . . . . . . 1210.0, Table 1210.1,
Table 1220.4.2
Joining and connections. . . . . . . . . . . . . . . . (see Joints and connections) Oxygen diffusion . . . . . . . . . . . . . . . . . . . . . . . . . 1210.4 POLYPROPYLENE (PP) PIPE OR TUBING
Definition. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 218.0
Ground source loop . . . . . . . . . . . . . . . . . Table 1703.2,
Table 1703.3
Hydronics . . . . . . . . . . . . . . . . . . . 1210.0, Table 1210.1
Joining and connections. . . . . . . . . . . . . . . . (see Joints
and connections)
POLYVINYL CHLORIDE (PVC) PIPE OR TUBING
Definition. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 218.0
Ground source loop. . . . . . . Table 1703.2, Table 1703.3
Hydronics . . . . . . . . . . . . . . . . . . . 1210.0, Table 1210.1
PORTABLE
CMC § 1703.3 Medium relevance — show source text
Table 1703.3
Hydronics . . . . . . . . . . . . . . . . . . . 1210.0, Table 1210.1,
Table 1220.4.2
Joining and connections. . . . . . . . . . . . . . . . (see Joints and connections) Oxygen diffusion . . . . . . . . . . . . . . . . . . . . . . . . . 1210.4 POLYPROPYLENE (PP) PIPE OR TUBING
Definition. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 218.0
Ground source loop . . . . . . . . . . . . . . . . . Table 1703.2,
Table 1703.3
Hydronics . . . . . . . . . . . . . . . . . . . 1210.0, Table 1210.1
Joining and connections. . . . . . . . . . . . . . . . (see Joints
and connections)
POLYVINYL CHLORIDE (PVC) PIPE OR TUBING
Definition. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 218.0
Ground source loop. . . . . . . Table 1703.2, Table 1703.3
Hydronics . . . . . . . . . . . . . . . . . . . 1210.0, Table 1210.1
PORTABLE
Cooling unit . . . . . . . . . . . . . . . . . . . . . . . . 104.2, 218.0
Evaporative cooler . . . . . . . . . . . . . . . . . . . 104.2, 218.0
Fire extinguishers . . . . . . . . . . . . . . . . . . . 513.2, 513.11
Heating appliance . . . . . . . . . . . . . . . . . . . 104.2, 203.0
Ventilating equipment. . . . . . . . . . . . . . . . . 104.2, 218.0
POSITIVE DISPLACEMENT COMPRESSOR
Refrigeration . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1112.2
POWER BOILER PLANT
Definition. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 218.0
PRESSURE
Design, definition . . . . . . . . . . . . . . . . . . . . . . . . . 218.0
Field test, definition . . . . . . . . . . . . . . . . . . . . . . . . 218.0
Imposing element, definition . . . . . . . . . . . . . . . . . 218.0
Limiting devices. . . . . . . . . . . . . . . . . . . . . 218.0, 904.5,
CMC § 1206.2 Medium 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 § 1210.0 Medium relevance — show source text
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
1211.6 Crossed-Linked Polyethylene (PEX) Pipe . . . . . . . . . . . . . . . . . . 263
1211.7 Cross-Linked Polyethylene/ Aluminum/Cross-Linked
Polyethylene (PEX-AL-PEX) Pipe. . 263
1211.8 Ductile Iron Pipe . . . . . . . . . . . . . . 263
1211.9 Polyethylene (PE) Plastic Pipe/Tubing. . . . . . . . . . . . 263
1211.10 Polyethylene/Aluminum/ Polyethylene (PE-AL-PE) . . . . . . . 264
1211.11 Polyethylene of Raised Temperature (PE-RT). . . . . . . . . . 264
1211.12 Polypropylene (PP) Pipe. . . . . . . . 264
1211.13 Polyvinyl Chloride (PVC) Pipe . . . 264
1211.14 Steel Pipe and Tubing . . . . . . . . . 265
1211.15 Stainless Steel Pipe and Joints. . . 265
1211.16 Joints Between Various Materials. . 265
1212.0 Valves. . . . . . . . . . . . . . . . . . . . . . 265
1212.1 General. . . . . . . . . . . . . . . . . . . . . 265
1212.2 Where Required . . . . . . . . . . . . . . 265
1212.3 Heat Exchanger . . . . . . . . . . . . . . 265
1212.4 Pressure Vessels . . . . . . . . . . . . . 265
1212.5 Pressure Reducing Valves . . . . . . 265
CMC § 1703.2 Medium relevance — show source text
Ground source loop. . . . . . . Table 1703.2, Table 1703.3
Hydronics . . . . . . . . . . . . . . . . . . . 1210.0, Table 1210.1,
Table 1220.4.2
Joining and connections. . . . . . . . . . . . . . . . (see Joints
and connections)
Oxygen diffusion . . . . . . . . . . . . . . . . . . . . . . . . . 1210.4
CROSS-LINKED POLYETHYLENE-ALUMINUM-CROSS-
LINKED POLYETHYLENE (PEX-AL-PEX)
PIPING OR TUBING
Definition. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 218.0
Hydronics . . . . . . . . . . . . . . . . . . . 1210.0, Table 1210.1
Joining and connections. . . . . . . . . . . . . . . . (see Joints
and connections)
– D –
DAMPERS
Automatically
operated . . . . . . . 606.8, 802.14, 802.14.1, E 502.10.2
Backdraft. . . . . . . . . . . . . . . . . . . 504.1.1, 504.4, 1106.6
Balancing. . . . . . . . . . . . . . . . . . . . . . . . . . . . .E 502.3.1
Ceiling radiation . . . . . . . . . . . . . . . . . . . . . 206.0, 606.3
Combination fire and smoke . . . . . . . . . . . 206.0, 606.4
Corridor. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 606.5
Definition. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 206.0
Economizers . . . . . . . . . . . . . . . . . . . . . . . . E 503.5.1.1
Fire . . . . . . . . . . . . . . . . . 206.0, 508.3.5.3, 508.3.5.3.1,
511.4.2, 516.2.6,
606.2, 606.8, 932.1
Fire and smoke, access to . . . . . . . . . . . . . . . . . . 606.8
Freedom from interference . . . . . . . . . . . . . . . . . . 606.9
Heating, ventilation,
and air conditioning . . . . . . . . . . . . . . . . . . . E 502.12
HVAC system tests of . . . . . . . . . . . . . . . . . . . . E 805.0
CMC § 205.0 Medium relevance — show source text
Towers . . . . . . . . . . . . . . . . . . . . . . . Chapter 11 (Part II)
Unit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 205.0, 904.9
COPPER OR COPPER
ALLOY PIPE AND TUBING . . . . . . . . . . . . . . . . . . . 1211.4
CORRUGATED STAINLESS STEEL
TUBING (CSST)
Bonding of . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1311.2
Definition. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 205.0
Support . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1310.3.5
Test pressure. . . . . . . . . . . . . . . . . . . . . . . . . . . . 1313.3
CREMATORIES
Factory built . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 925.3
CROSS-LINKED POLYETHYLENE (PEX)
PIPING OR TUBING
Definition. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 218.0
Ground source loop. . . . . . . Table 1703.2, Table 1703.3
Hydronics . . . . . . . . . . . . . . . . . . . 1210.0, Table 1210.1,
Table 1220.4.2
Joining and connections. . . . . . . . . . . . . . . . (see Joints
and connections)
Oxygen diffusion . . . . . . . . . . . . . . . . . . . . . . . . . 1210.4
CROSS-LINKED POLYETHYLENE-ALUMINUM-CROSS-
LINKED POLYETHYLENE (PEX-AL-PEX)
PIPING OR TUBING
Definition. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 218.0
Hydronics . . . . . . . . . . . . . . . . . . . 1210.0, Table 1210.1
Joining and connections. . . . . . . . . . . . . . . . (see Joints
and connections)
– D –
DAMPERS
Automatically
operated . . . . . . . 606.8, 802.14, 802.14.1, E 502.10.2
Backdraft. . . . . . . . . . . . . . . . . . . 504.1.1, 504.4, 1106.6
CMC § 0.04 Medium relevance — show source text
(8) Listing and approval.
(a) The concentration of oxygen in the undiluted flue products of oil or liquid fuel burners shall in no case be less than 3 percent nor exceed 10 percent and shall be in accordance with performance standards and shall be consistent with the listing and approval of the equipment.
(b) The allowable limit of carbon monoxide shall not exceed 0.04 percent.
(c) The flue gas temperature of an oil appliance, as taken on the appliance side of the draft regulator, shall not exceed applicable performance standards and shall be consistent with the listing and approvals of the equipment.
(9) The oxygen figures shall not apply where there is an approved oxygen trim system on the burner that is designed for that use, including a low oxygen interlock where approved by the Authority Having Jurisdiction.
(10)Supervision shall be as follows:
(a) Supervised startup shall be required to verify the safe operation of an oil or liquid fuel burner and to provide documentation that operation is consistent with this code, listing, and approval. Supervised startup shall be required for liquid fuel burners in Section C 109.1(2) through Section C 109.1(5). Supervised startup requires that the liquid-fuel burner shall be tested in the presence of the mechanical official in a manner set forth by the Authority Having Jurisdiction before the installation is approved. Testing shall include safety and operating controls, input, flue gas analysis, and venting. Flue gas shall be tested at high, medium, and low fires. Provisions shall be made in the system to allow a firing test in warm weather. After completion of the test of newly installed oil or liquid fuel burner equipment, as provided in this section, the installer shall file with the Authority Having Jurisdiction complete records of the test on a form approved by the Authority Having Jurisdiction. The tag stating the date of the test and the name of the tester shall be
attached to the appliance at the main valve.
(b) Oil and liquid fuel burners of 1 000 000 Btu/h (293 kW) input or more require a supervised startup in accordance with Section C 108.1(10)(a).
(c) Installation of oxygen trim systems, modulating dampers, or other draft control or combustion devices require a supervised startup in accordance with Section C 108.1(10)(a).
2025 CALIFORNIA MECHANICAL CODE 399
), Copyright © 2025 IAPMO, and may not be used for any other purpose or distributed to any other persons or parties.
APPENDIX C
(d) Direct-fired heaters shall require a supervised startup in accordance with Section C 108.1(10)(a).
(11)The complete control diagram of the installation and operating instructions shall be supplied and posted by the installer of the appliance.
C 109.0 Special Requirements Based on Btu/h Input.
C 109.1 General.
(1) Zero to 400 000 Btu/h (0 kW to 117 kW) per burner.
(a) One approved manual shutoff valve lever handle.
(b) One approved fuel oil filter, installed on the supply piping.
(c) Approved automatic safety shutoff valve to provide 100 percent shutoff of all oil.
(d) A flame safeguard control capable of providing 100 percent shutoff in the event of flame failure. Flame failure response timing shall not exceed the control manufacturer’s instructions.
CMC § 1309.1 Medium relevance — show source text
(1) The manufacturer of the concentrator unit shall be permitted to use such components and arrangement of such components as needed to produce oxygen complying
with Section 1309.1 in the quantity as required by the facility, except where otherwise specifically defined in this code.
(2) Air receivers and oxygen accumulators, where used, shall comply with Section VIII.1, “Unfired Pressure Vessels,” of the ASME Boiler and Pressure Vessels Code and be provided with overpressure relief valves. [NFPA 99:5.1.3.9.1.5]
1309.6 Supply Air Quality. The supply air to the concentrator(s) shall be of a quality to ensure the oxygen concentrator unit can produce oxygen complying with Section 1309.1 and shall not be subject to normally anticipated contamination (e.g., vehicle or other exhausts, gas leakage, discharge from vents, flooding). [NFPA 99:5.1.3.9.1.6]
1309.7 Electrical Components. The oxygen concentrator supply unit and any associated electrical equipment shall be provided with, at a minimum, the following electrical components:
(1) Either a disconnect switch for each major electrical component or a single disconnect that deactivates all electrical components in the concentrator unit.
(2) Motor starting devices with overload protection for any component with an electrical motor over 2 hp (1.5 kW).
[NFPA 99:5.1.3.9.1.7]
1309.8 Vent Valve. A vent valve shall be provided as follows:
(1) Located on the source side of the concentrator outlet isolation valve to permit the operation of the oxygen concentrator unit for validation, calibration, and testing while the unit is isolated from the pipeline system.
(2) Sized to allow for at least 25 percent of the oxygen concentrator unit flow.
(3) Vented to a location compliant with Section 1309.8.1.
[NFPA 99:5.1.3.9.1.8]
1309.8.1 Venting of Relief Valves. Indoor supply systems shall have all relief valves vented per Section 1308.2(4) through Section 1308.2(9). [NFPA 99:5.1.3.3.3.2]
1309.9 Valved Sample Port. A DN8 (NPS 1/4) valved sample port shall be provided near the oxygen concentration monitor sensor connection for sampling of the gas from the oxygen concentrator unit. [NFPA 99:5.1.3.9.1.9]
1309.10 Suitable Filter. At least one 0.1 micron filter suitable for oxygen service shall be provided at the outlet of the oxygen concentrator supply unit. [NFPA 99:5.1.3.9.1.10]
1309.11 Check Valve. A check valve shall be provided at the outlet of the oxygen concentrator supply unit to prevent backflow into the oxygen concentrator supply unit and to allow service to the unit. [NFPA 99:5.1.3.9.1.11]
1309.12 Outlet Valve. An outlet valve shall be provided to isolate all components of the oxygen concentrator from the pipeline with the following characteristics:
(1) The valve shall have both manual and automatic actuation with visual indication of open or closed.
2025 CALIFORNIA PLUMBING CODE 279
CMC § 2.95 Medium relevance — show source text
00|2.95|2.20|1.45|3.00|2.35|1.25|DR| |Cold-formed steel framing
(minimum penetration of steel
thickness plus 3 threads)|#8 screw into 33 mil steel or
thicker|8|3.00|2.55|1.60|0.60|3.00|1.80|DR|DR| |Cold-formed steel framing
(minimum penetration of steel
thickness plus 3 threads)|#8 screw into 33 mil steel or
thicker|12|3.00|1.80|DR|DR|3.00|0.65|DR|DR| |Cold-formed steel framing
(minimum penetration of steel
thickness plus 3 threads)|#10 screw into 33 mil steel|6|4.00|3.50|2.70|1.95|4.00|2.90|1.70|0.55| |Cold-formed steel framing
(minimum penetration of steel
thickness plus 3 threads)|#10 screw into 33 mil steel|8|4.00|3.10|2.05|1.00|4.00|2.25|0.70|DR| |Cold-formed steel framing
(minimum penetration of steel
thickness plus 3 threads)|#10 screw into 33 mil steel|12|4.00|2.25|0.70|DR|3.70|1.05|DR|DR| |Cold-formed steel framing
(minimum penetration of steel
thickness plus 3 threads)|#10 screw into 43 mil steel or
thicker|6|4.00|4.00|4.00|3.60|4.00|4.00|3.45|2.70| |Cold-formed steel framing
(minimum penetration of steel
thickness plus 3 threads)|#10 screw into 43 mil steel or
thicker|8|4.00|4.00|3.70|3.00|4.00|3.85|2.80|1.80| |Cold-formed steel framing
(minimum penetration of steel
thickness plus 3 threads)|#10 screw into 43 mil steel or
thicker|12|4.00|3.85|2.80|1.80|4.00|3.05|1.50|DR| |For SI: 1 inch = 25.4 mm, 1 pound per square foot (psf) = 0.0479 kPa, 1 pound per square inch = 0.00689 MPa.
DR = design required, o.c. = on center.
a. Cold-formed steel framing shall be minimum 33 ksi steel for 33 mil and 43 mil steel and 50 ksi steel for 54 mil steel or thicker.
b. Screws shall comply with the requirements of AISI S240.
c. Foam sheathing shall have a minimum compressive strength of 15 pounds per square inch in accordance with ASTM C578 or ASTM C1289.|For SI: 1 inch = 25.4 mm, 1 pound per square foot (psf) = 0.0479 kPa, 1 pound per square inch = 0.00689 MPa.
DR = design required, o.c. = on center.
a. Cold-formed steel framing shall be minimum 33 ksi steel for 33 mil and 43 mil steel and 50 ksi steel for 54 mil steel or thicker.
b.CMC § 12-7 Medium relevance — show source text
12-7A-4A.3 Referenced document.
- ASTM E108. Standard Test Methods for Fire Tests of Roof Coverings.
- California Building Code, Chapter 7A.
12-7A-4A.4 Definitions.
- Deck boards. Horizontal members that constitute the exposed surface of the ancillary structure.
- Heat release rate. The net rate of energy release as measured by oxygen depletion calorimetry.
12-7A-4A.5 Test assembly.
- Size. The overall size of the test deck shall be nominally 24 x 24 inches (610 x 610 mm) unless width variation of deck boards requires an increase in overall deck width (i.e., the direction of joists) in order to meet the overall dimensions. The length of individual deck boards shall be 24 inches (610 mm).
- Joists. The deck is supported by two nominal 2 x 6 Douglas-fir joists running perpendicular to the deck boards, and constructed with a 16-inch (406 mm) center-to-center spacing. A comparable species that may be more commonly used for structural framing of decks in a given region can be substituted for Douglas-fir.
- Deck board spacing and fastening. Edge-to-edge spacing and method of attachment shall conform to the manufacturer’s installation recommendations. The front deck board shall be flush with the ends of the joists, and the rear deck board shall overhang the end of the joists by 1 inch (25 mm). 3.1. In the absence of recommended installation guidance, the edge-to-edge spacing shall be [3] / 16 inch (5 mm) with boards mechanically attached to the joists using deck screws. 3.2. If nominal 6-inch-wide (152 mm) deck boards are used, a total of five boards shall be used for each deck. Changing the board width could change the number of deck boards.
12-7A-4A.6 Materials.
- Cross-sectional dimension. All deck board materials are to have cross-sectional dimensions equivalent to use in service.
- Description. The material under test should be described as completely as possible (unit weight, thickness, width and general information regarding composition).
- Condition of test material. Prior to testing, all materials (deck boards and joist material) shall be conditioned to a constant weight or for a minimum of 30 days at 73 ± 4°F (23 ± 2°C) and 50 ± 5 percent relative humidity, whichever occurs first. Constant weight shall be defined as occurring when the change in test material weight is less than or equal to 2 percent in a 24-hour period.
Note: The moisture content of joists shall be between 8- and 10-percent moisture content.
12-7A-4A.7 Under-deck flame test.
12-7A-4A.7.1 Equipment.
- Burner. A 12- x 12-inch (300 x 300 mm) diffusion burner shall be used. Natural gas, methane or propane shall be supplied to the burner through a metered control system. The gas supply to the burner shall produce a net heat output of 80 ± 4 kW throughout the flame exposure. Burner output can be determined from HRR or calculated from the gas flow rate, temperature and pressure.
- Oxygen depletion calorimeter. The equipment shall include a hood, associated ducting and instrumentation to provide HRR data by oxygen depletion calorimetry.
Frequently asked questions
What exactly does “oxygen barrier” mean in the CMC?
The CMC requires that PEX and PE‑RT tubing used in closed hydronic systems contain an oxygen barrier (§ 1210.4), but § 1210.4 does not define a numeric oxygen transmission limit or list accepted test methods — you must rely on product literature, referenced standards, or AHJ acceptance.
If I use glycol, can I skip an oxygen barrier?
The code text in § 1210.4 does not provide an exception for fluid type. The requirement is that PEX and PE‑RT tubing in closed hydronic systems contain an oxygen barrier; if tubing permits oxygen diffusion, then § 1210.4.2 requires non‑ferrous/corrosion‑resistant components. The use of glycol is not addressed in § 1210.4.
Are steel pumps or cast‑iron heat exchangers allowed?
Not in vented or non‑oxygen‑barrier portions of the loop — § 1210.4.1 and § 1210.4.2 require non‑ferrous or other corrosion‑resistant materials where oxygen ingress is possible.
Where do I find the definition of a “non‑oxygen barrier closed‑loop system”?
See the hydronics definitions in the code (definitions chapter referenced by § 218.0 and hydronics definitions) to determine system classification; that classification determines applicability of § 1210.4.2.
The code doesn’t give a test standard — how do inspectors verify compliance?
Inspectors typically verify manufacturer literature or product listings showing an integrated oxygen barrier and approve materials accordingly; because § 1210.4 is silent on test methods, AHJs commonly rely on referenced product standards or manufacturer certification. The code text itself does not specify a test.
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