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• Provide two permanent openings to allow
circulation of combustion air.
• Make each opening 199 square inches if they
provide indoor air, and 100 square inches for
outdoor air.
• If the unit is installed in a mechanical closet,
provide a 24" (600mm) clearance in front of
the unit to the door.
• If combustion air will be provided through a
duct, size the duct to provide 60 cubic feet of
fresh air per minute.
Supply combustion air to the units as per the National Fuel Gas Code, ANSI Z223.1-
latest edition and in Canada, in accordance with the Natural Gas and Propane Installation
Code CSA B149.1-latest edition.
Combustion Air
Openings supplying indoor air
20" (500mm)
20" (500mm)
10" (150mm)
10" (150mm)
