Page 11
Equipment In Confined Space
All Air From Outside
OUTLET AIR
INLET AIR
WATER
HEATER
CHIMNEY
OR OIL
VENT
Figure 13
NOTE Each air duct opening shall have a free area of at least one
square inch (6.4 square centimeters) per 2,000 Btu (586 W) per hour
of the total input rating of all equipment in the enclosure. If the equip
ment room is located against an outside wall and the air openings
communicate directly with the outdoors, each opening shall have a
free area of at least one square inch (6.4 square centimeters) per
4,000 Btu (1172 W) per hour of the total input rating of all other equip
ment in the enclosure.
OIL
FURNACE
When ducts are used, they shall be of the same cross−sec-
tional area as the free area of the openings to which they
connect. The minimum dimension of rectangular air ducts
shall be no less than 3" (76 mm). In calculating free area,
the blocking effect of louvers, grilles, or screens must be
considered. If the design and free area of protective cover-
ing is not known for calculating the size opening required, it
may be assumed that wood louvers will have 20 to 25 per-
cent free area and metal louvers and grilles will have 60 to
75 percent free area. Louvers and grilles must be fixed in
the open position or interlocked with the equipment so that
they are opened automatically during equipment operation.
CAUTION
The barometric control shall be in the same atmo-
spheric pressure zone as the combustion air inlet to
the furnace. Deviation from this practice will cause
improper burner operation and may result in a fire
hazard or injury.
