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• Provide two permanent openings to allow cir-
culation of combustion air.
• Make each opening 180 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" 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 NSCNGPIC.
Combustion Air
Openings supplying indoor air
20"
9"
20"
9"
