Air Supply to Boiler Houses

Incomplete combustion may generate carbon monoxide - CO - in the boiler - re-ignition may cause disastrous effects on both personnel and property

For proper combustion and safety precautions it is necessary to provide the boiler room with appropriate openings for fresh air supply. Temporary air intakes such as windows and doors should be avoided since they may be closed (and often they are when persons in the boiler room are feeling cold) - cutting off the boiler's air supply.

If combustion air supply is limited the fire starts to smoke. Incomplete combustion occur and carbon monoxide is generated. If the fire goes out before the flame detection system acts to close the fuel safety shutoff valve, accumulated fuel may re-ignite when oxygen seeps in through cracks and crevices. A furnace explosion may occur with disastrous effects on personnel and property.

  • adequate air supply is required to minimize the possibility of explosion

Codes addressing the amount of combustion air or size of the opening in the walls for combustion air in the boiler room:

  • ASME CSD-1- Controls and Safety Devices for Automatically Fired Boilers, 1992 with addendum 1a 1993. section CG-260 Combustion Air.
  • ASME Section VI Recommended Rules for the Care and Operations of Heating Boilers.
  • NFPA 54 - National Fuel Gas Code, 1992, section 5.3 Air for Combustion and Ventilation.
  • NFPA 31 - Installation of Oil Burning Equipment, 1992, section 1-5 Air for Combustion and Ventilation.
  • BOCA - National Mechanical Code, 1990, article 10, Combustion Air.
  • SBCCI- Standard Mechanical Code, 1991, section 305 Combustion and Ventilation Air.
  • American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) Handbook - Fundamentals, 1993, Chapter 15, page 15.9 Air For Combustion.

ASME CSD-1- Controls and Safety Devices for Automatically Fired Boilers, 1992 with addendum 1a 1993. section CG-260 Combustion Air

Sections covers the requirements for combustion air intakes.

The American Society of Mechanical Engineers, ASME

ASME Section VI Recommended Rules for the Care and Operations of Heating Boilers

Reference 6.04 states:

The boiler room must have adequate air supply to permit clean, safe combustion and to minimize soot formation. An unobstructed air opening should be provided. It may be sized on the basis of 1-square inch free area per 2000-btu/hr maximum fuel input of combined burners located in the boiler room, or as specified in the National Fire Protection Association standards for oil and gas burner installations for the particular job conditions. The boiler room air supply openings must be kept clear at all times.

From experience the ASME rule of 1-square inch free area per 2000-btu/hr (Unit Converter) maximum fuel input of combined burners located in the boiler room works. I general rounded up to the next common size.

NFPA 54 - National Fuel Gas Code, 1992, section 5.3 Air for Combustion and Ventilation

provides requirements for installation and operation of gas piping, equipment installations and venting. It is the accepted national measure for all fuel gas installations.

National Fire Protection Association, NFPA

Gas fuels:

Minimum No. openings required 2
Outdoor opening (sq. in./Btu h) 1/4000
Vertical ducts (sq. in./Btu h) 1/4000
Horizontal ducts (sq. in./Btu h) 1/2000
Ducts same as opening yes
Minimum duct dimension  (inches) 3
Louver & grill free area opening
Free area allowance, wood* 20-25%
Free area allowance, metal* 60-75%
Damper interlocked yes

* It is assumed that wood louvers and grilles have 20-25% free area. Metal louvers and grilles 60-75% respectively.

NFPA 31 - Installation of Oil Burning Equipment, 1992, section 1-5 Air for Combustion and Ventilation

Covers minimum requirements for safety to life and property from fire in the installation of oil burners and the equipment used in connection with them.

Oil fuels:

Minimum No. openings required 2
Outdoor opening (sq. in./Btu h) 1/4000
Vertical ducts (sq. in./Btu h) 1/4000
Horizontal ducts (sq. in./Btu h) 1/2000
Ducts same as opening yes
Minimum duct dimension (inches) 3
Louver & grill free area opening
Free area allowance, wood* 20-25%
Free area allowance, metal* 60-75%

BOCA - National Mechanical Code, 1990, article 10, Combustion Air

Building Officials and Code Administrators International (BOCA)

All fuels:

Minimum No. openings required 2
Outdoor opening (sq. in./Btu h) 1/4000
Vertical ducts (sq. in./Btu h) 1/4000
Horizontal ducts (sq. in./Btu h) 1/2000
Minimum duct dimension (inches) 3
Free area allowance, wood 25%
Free area allowance, metal 75%
Damper interlocked yes

SBCCI- Standard Mechanical Code, 1991, section 305 Combustion and Ventilation Air.

Southern Building Code Congress International, SBCCI

Gas and Oil fuels:

Minimum No. openings required 2
Outdoor opening  (sq. in./Btu h) 1/4000
Vertical ducts (sq. in./Btu h) 1/4000
Horizontal ducts (sq. in./Btu h) 1/2000
Ducts same as opening yes
Minimum duct dimension (inches) 3

Solid fuels:

Minimum No. openings required 2
Outdoor opening  (sq. in./Btu h) 2/1000
Minimum duct dimension  (inches) 3
Louver & grill free area opening

American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) Handbook - Fundamentals, 1993, Chapter 15, page 15.9 Air For Combustion

ASHRAE

Related Topics

  • Combustion - Boiler house topics - fuels like oil, gas, coal, wood - chimneys, safety valves, tanks - combustion efficiency

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