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

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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. These articles answer most questions about central hot water heating system troubleshooting, inspection, diagnosis, and repairs. 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 the REFERENCES for this article. Utiskul, writing for the NFPA discusses NFPA 54 cited by U.S. heating appliance manufacturers for combustion air standards, and in Canada, 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. It 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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Continue reading at COMBUSTION AIR INLET AUTOMATIC LOUVERS or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.

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Or see COMBUSTION AIR for TIGHT BUILDINGS

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