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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
and in Canada, in accordance with CSA-B149.1.
Combustion Air
Openings supplying indoor air
10" (250mm)
20" (500mm)
10" (250mm)
20" (500mm)
Provide adequate combustion air so as to not create negative pressure within the building.
