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INSTALLATION
2.15.1 Combustion air from outside the building
Air supplied from outside the building must be provided through two
permanent openings. For each unit these two openings must have a
free area of not less than one square inch for each 4000 BTUs input of
the equipment or 750 square inches of free area. The free area must
take into account restrictions such as louvers and bird screens.
2.15.2 Combustion air from inside the building
When combustion air is provided from within the building, it must
be supplied through two permanent openings in an interior wall.
Each opening must have a free area of not less than one square inch
per 1000 BTUH of total input or 3000 square inches of free area. The
free area must take into account any restrictions, such as louvers.
2.15.3 Ducted combustion air
For ducted combustion air installations, the air ductwork must then be
attached directly to the air inlet connection on the sheet metal enclosure.
In a ducted combustion air application, the combustion air duct-
ing pressure losses must be taken into account when calculating
the total maximum allowable venting run.
For additional details, see “Appendix N - Exhaust terminals and
Air inlet Clearances”.
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