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Chapter 10 — BOILERS AND PRESSURE VESSELS

1004.3 Closed-Type Systems. Closed-type systems shall

California Mechanical Code (Title 24, Part 4) · 2019 edition · updated 2026-09-10 · California

Italicized text is a California amendment to the model code, as printed in the official publication.

have an airtight tank or other approved air cushion that will

INSTALLED EQUIVALENT
DIRECT RADIATION2
(square feet)		 TANK CAPACITY
(gallons)
Up to 350
 18

Up to 450
 21

Up to 650
 24

Up to 900
 30

Up to 1100
 35

Up to 1400
 40

Up to 1600
 2 to 30

Up to 1800
2 to 30

Up to 2000
2 to 35


Up to 2400

2 to 40

Notes:

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 m2) 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.

202 2019 CALIFORNIA MECHANICAL CODE

BOILERS AND PRESSURE VESSELS

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)
100
 9
 15
200
 17
 30
300
 25
 45
400
 33
 60
500
 42
 75
1000
 83
 150


2000

165		 300

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.

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▸Contents — California Mechanical Code (Title 24, Part 4)
California Mechanical Code (Title 24, Part 4)
  1. Chapter 1 — GENERAL CODE PROVISIONS
  2. Chapter 2 — DEFINITIONS
  3. Chapter 3 — GENERAL REGULATIONS
  4. Chapter 4 — VENTILATION AIR
  5. Chapter 5 — EXHAUST SYSTEMS
  6. Chapter 6 — DUCT SYSTEMS
  7. Chapter 7 — COMBUSTION AIR
  8. Chapter 8 — CHIMNEYS AND VENTS
  9. Chapter 9 — INSTALLATION OF SPECIFIC APPLIANCES
  10. ▸Chapter 10 — BOILERS AND PRESSURE VESSELS
    Overview
    1. 1001.0 General.1001.1 Applicability. The requirements of this …
    2. 1001.2 Boiler Rooms and Enclosures. Boiler rooms and
    3. 1001.3 Air for Combustion and Ventilation. Air for
    4. 1001.4 Drainage. For heating or hot-water-supply boiler
    5. 1001.5 Mounting. Equipment shall be set or mounted on a
    6. 1001.6 Chimneys or Vents. Boilers shall be connected to
    7. 1002.1 General.1002.0 Standards. Pressure vessels shall be con…
    8. 1002.2 Oil-Burning Boilers. Oil-burning boilers shall
    9. 1002.3 Electric Boilers. Electric boilers shall be listed and
    10. 1002.4 Solid-Fuel-Fired Boilers. Solid-fuel-fired boilers
    11. 1002.5 Dual Purpose Water Heater. Water heaters utilized for c…
    12. 1003.1 Safety Requirements.1003.0 Detailed Requirements. The c…
    13. 1003.2 Controls. Required electrical, mechanical, safety,
    14. 1004.4 Minimum Capacity of Closed-Type Tank. The
    15. 1003.3 Gauges. Steam boilers shall be provided with a
    16. 1003.4 Stack Dampers. Stack dampers on boilers fired
    17. 1003.5 Welding. Welding on pressure vessels shall be done
    18. 1004.1 General.1004.0 Expansion Tanks. An expansion tank shall…
    19. 1004.2 Open-Type Expansion Tanks. Open type expansion tanks sh…
    20. 1004.3 Closed-Type Systems. Closed-type systems shall
    21. 1005.2 Discharge Piping. The discharge piping serving a
    22. 1005.5 Vacuum Relief Valve. Hot-water heating systems
    23. 1008.0 Low-Water Cutoff.1008.1 General. Hot water boilers and …
    24. 1005.3 Splash Shield. Where the operating temperature
    25. 1005.4 Hazardous Discharge. Where the discharge from
    26. 1010.1 General. 1010.0 Clearance for Access. Where boilers are…
    27. 1010.2 Power Boilers. Power boilers having a steam-generating …
    28. 1010.3 Steam-Heating Boilers, Hot Water Boilers, andPower Boil…
    29. 1012.1 General.1012.0 Operating Adjustments and Instructions. …
    30. 1013.1 General.1013.0 Inspections and Tests. An installation f…
    31. 1011.1 General. 1011.0 Boilers, Stokers, and Steam Generators.…
    32. 1013.2 Operating Permit. It shall be unlawful to operate a
    33. 1013.3 Maintenance Inspection. The Authority Having
    34. 1013.4 Power and Miniature Boilers. Power boilers and
    35. 1013.6 Automatic Steam-Heating Boilers. Automatic
    36. 1013.7 Unfired Pressure Vessels. Unfired pressure vessels shal…
    37. 1014.1 General. Pressure Vessels. Boilers and pressure vessels…
  11. Chapter 11 — REFRIGERATION
  12. Chapter 12 — HYDRONICS
  13. Chapter 13 — FUEL GAS PIPING
  14. Chapter 14 — PROCESS PIPING
  15. Chapter 15 — SOLAR ENERGY SYSTEMS
  16. Chapter 16 — STATIONARY POWER PLANTS
  17. Chapter 17 — REFERENCED STANDARDS
  18. Appendix A — RESIDENTIAL PLAN EXAMINER REVIEW FORM FOR HVAC SY…
  19. Appendix B — PROCEDURES TO BE FOLLOWED TO PLACE GAS EQUIPMENT …
  20. Appendix C — INSTALLATION AND TESTING OF OIL (LIQUID) FUEL-FIR…
  21. Appendix D — FUEL SUPPLY: MANUFACTURED/MOBILE HOME PARKS AND R…
  22. Appendix E — SUSTAINABLE PRACTICES
  23. Appendix F — SIZING OF VENTING SYSTEMS AND OUTDOOR COMBUSTION …
  24. Appendix G — EXAMPLE CALCULATION OF OUTDOOR AIR RATE

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