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Installation instructions
Fuel Gas Code. Consult a HVAC specialist if your air
infiltration rate is questionable.
The space must have two permanent openings, one
commencing within 12 inches of the top and one
commencing within 12 inches of the bottom of the
enclosure. Each opening must have a minimum free
area of one square inch per:
• 1000 Btu/hr if all air is taken from inside the building
• 2000 Btu/hr if all air is taken from the outside by
horizontal ducts
• 4000 Btu/hr if all air is taken from the outside by
direct openings or vertical ducts.
Or the space must be provided with one permanent
opening or duct that is within 12 inches of the ceiling of
the enclosure. This opening must have a minimum free
area of one square inch per:
• 3000 Btu/hr if all air is taken from the outside by a
direct opening or vertical duct.
Louvers, grills and screens have a blocking effect. If the
effective free area is not known, increase the sizes of
your openings by 300% if your louvers are wood and by
35% if your louvers are metal. Refer to the National Fuel
Gas Code for complete information.