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Mobile home furnace (C) Daniel FriedmanCombustion Air Requirements for Power Burners

Combustion Air Guidelines

Combustion air defects & hazards for power burners:

This article series explains how to recognize and fix combustion air defects on heating appliances such as boilers, furnaces, and water heaters.

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Our photo at page top shows an oil fired furnace installed in a closet with an airtight door; there was no outside combustion air supply. The heating system could not work properly nor safely in this home.

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Combustion Air Requirements Specifications for Power Burners

For combustion air requirements for power burner fired heating appliances we excerpt research by Utiskul (2012) cited in theReferences or Citations for this article.

Utiskul, writing for the NFPA discusses the National Fuel Gas Code - NFPA 54 cited by U.S. heating appliance manufacturers for combustion air standards, and in Canada, the Canadian Natural gas and propane installation code CSA B149.1-10 (which gives different criteria).

Excerpting notes on combustion air for power burners the author notes:

NFPA 54 requires the largest outdoor openings for combustion air in comparison to the other referenced guidelines. The opening free area required by NFPA 54 ranges from 0.33 to 1 square inch per kBtu/hr input rating, depending on the number of the openings and how they communicate with the outdoors.

The other guidelines require combustion air openings with free area ranging from 0.08 to 0.14 square inches per kBtu/hr, which is consistent with providing an additional approximately 30% air supply to the combustion process. CSA B149.1-10 contains a separate provision for appliances equipped with power burners to supply combustion air with outdoor openings sized to 0.03 square inches per kBtu/hr of the total burner input rating.

Power burner boilers have the highest range of energy input ratings (60,000 to 83,600,000 Btu/hr) in comparison to that of water heaters (60,000 to 40,300,000 Btu/hr) and furnaces (30,000 to 9,800,000 Btu/hr).

A majority of the manufacturers (60%) included in this study reference NFPA 54 for combustion air requirements (0.33 to 1 square inches per kBtu/hr input) for their power burner appliances with energy inputs ranging from 30 to 92,000 kBtu/hr.

Of the 25 manufacturers, eight recommend that combustion air be provided by openings sized to 0.03 to 0.75 square inches per kBtu/hr of the total appliance input rating from 150 to 83,600 kBtu/hr.

The opening size in accordance January 30, 2012 QMS QA ID No. 1103894.000 B0F0 0112 YU01 50 with these eight manufacturers is approximately 25% to 97% smaller than that of the NFPA 54 requirements. The remaining manufacturers recommend combustion air requirements based on a specified volumetric flow rate from 0.24 to 0.47 cfm per kBtu/hr of appliance input rating. 

Based on the review of available literature data, a review of the manufacturer’s requirements for combustion air, the investigation of the combustion air required for power burners, and the theoretical analysis of air flows through openings, sizing criteria for combustion air openings for power burner appliances are theorized as follows:

A minimum opening area of 0.2 square inches per kBtu/hr input rating for power burner appliances equipped with a draft control device; and

A minimum opening area of 0.1 square inches per kBtu/hr input rating for power burner appliances that require no dilution of flue gases.

Based on the theoretical analysis provided in this study, these theorized combustion air requirements should provide an adequate amount of combustion air for proper appliance operation and will optimize overall building efficiency by reducing unnecessary area in openings. I

t is strongly recommended the theorized sizing criteria be validated through fullscale field experiments, which will provide a basis for new code development. - Utiskul (2012)

Combusion Air for Power Burners, Research & Standards


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Citations & References

In addition to any citations in the article above, a full list is available on request.

  • 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.
  • BOCA - National Mechanical Code, 1990, article 10, Combustion Air.
  • NFPA 31 - Installation of Oil Burning Equipment, 1992, section 1-5 Air for Combustion and Ventilation.
  • NFPA 54/ ANSI Z223.1, National Fuel Gas Code, for gas-fired boilers [PDF] (2024) (First Public Review Draft), American Gas Association - Excerpt:

    NOTE: This preprint of the 2024 National Fuel Gas Code is provided for the convenience of the reviewer. NFPA’s Terra online draft is the official source for information. Please visit www.nfpa.org/54 for official drafts and reports.

    NFPA 54, ANSI Z223.1 provides minimum safety requirements for the design and installation of fuel gas piping systems in homes and other buildings. -(ocal copy saved as 2024-NFGC-First-Revision-Draft.pdf)
  • NFPA 85: Boiler and Combustion Systems Hazards Code: NFPA 85 contributes to operating safety and prevents explosions and implosions in boilers with greater than 12.5 MMBTUH, pulverized fuel systems, and heat recovery steam generators.
  • NFPA 87: Recommended Practice for Fluid Heaters, This recommended practice provides safety guidance for fluid heaters and related equipment to minimize fire and explosion hazards that can endanger the fluid heater, the building, or personnel
  • SBCCI- Standard Mechanical Code, 1991, section 305 Combustion and Ventilation Air.
  • Axtman, William H., "Combustion Air Requirements: The Forgotten Element in Boiler Rooms", Grayh Gull Associates, retired executive director of the American Boiler Manufacturers Association, National Board Technical Series, Winter 1995 National Board Bulletin. Retrieved 26 January 2015, original source: http://www.nationalboard.org/index.aspx?pageID=164&ID=191
  • Nussbaumer, Thomas. "Combustion and co-combustion of biomass: fundamentals, technologies, and primary measures for emission reduction." Energy & fuels 17, no. 6 (2003): 1510-1521.
  • Utiskul, Yunyong P., Wu, Neil P., Biteau, Hubert, "Combstion Air Requirements for Power Burner Appliances, Final Report", The Fire Protection Research Foundation, The Fire Protection Research Foundation
    One Batterymarch Park Quincy, MA, USA 02169-7471 Email: foundation@nfpa.org http://www.nfpa.org/foundation, retrieved 25 Jan 2015, original source: http://www.nfpa.org/~/media/files/research/research%20foundation/rfcombustionairrequirements.ashx,

    Executive Summary:

    Gas-fired appliances require combustion air to properly function. Adequate air is necessary for supporting combustion of the appliance burner, dilution of flue gas, and proper ventilation of the space where the appliance is installed.

    Current standards and model codes outline requirements and methods to supply the combustion air. O

    ne method is to provide outdoor combustion air through openings or air ducts communicating with the outdoors through natural ventilation. Most standards require the outdoor opening(s) be prescriptively sized based on the total energy input rating of the appliance.

    However, in the United States, the current standards contain no separate provisions to address the opening size supplying the combustion air for commercial/industrial sized appliances, which typically have a high energy input rating of greater than 300 kBtu/hr and are equipped with a power burner unit.

    As a result, the opening(s) can be excessively sized when determined based on the current standards. This research project establishes minimum outdoor combustion air requirements specific to gasfired appliances utilizing power burners with input ratings no greater than 12.5 MBtu/hr.

    A review of the available literature, engineering guidelines, and current standards and model codes related to combustion air requirements was performed. This report provides an understanding of the technical basis for the existing provisions for combustion air and their applicability to power burner appliances.

    This report also identifies the range of energy input ratings for gasfired appliances equipped with power burners, and compares the combustion air requirements specified by a range of appliance manufacturers.

    A theoretical model for air flow through openings was developed and the modeling results, together with the data gathered through the literature review, were used to provide a baseline to establish the theorized combustion airrequirements suitable for power burner appliances.
  • In addition to citations & references found in this article, see the research citations given at the end of the related articles found at our suggested

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