Lennox EL180DFE Installation Instructions Manual page 6

Elite series
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outside the space containing the furnace. This is especially
important when the furnace is mounted on a platform in a
confined space such as a closet or small equipment room.
Even a small leak around the base of the unit at the platform
or at the return air duct connection can cause a potentially
dangerous negative pressure condition. Air for combustion
and ventilation can be brought into the confined space either
from inside the building or from outside.
CHIMNEY
OR GAS
VENT
FURNACE
NOTE - Each opening shall have a free area of at least one square
2
inch (645 mm
) per 1,000 Btu (.29 kW) per hour of the total input rat­
ing of all equipment in the enclosure, but not less than 100 square
2
inches (64516 mm
).
FIGURE 2
Air from Inside
If the confined space that houses the furnace adjoins a
space categorized as unconfined, air can be brought in by
providing two permanent openings between the two
spaces. Each opening must have a minimum free area of 1
2
square inch (645 mm
) per 1,000 Btu (.29 kW) per hour of
EQUIPMENT IN CONFINED
SPACE ALL AIR FROM INSIDE
WATER
HEATER
OPENINGS
(To Adjacent
Room)
total input rating of all gas-fired equipment in the confined
space. Each opening must be at least 100 square inches
2
(64516 mm
). One opening shall be within 12 inches (305
mm) of the top of the enclosure and one opening within 12
inches (305 mm) of the bottom. See figure 2.
Air from Outside
If air from outside is brought in for combustion and ventila­
tion, the confined space must have two permanent open­
ings. One opening shall be within 12 inches (305 mm) of the
top of the enclosure and one opening within 12 inches (305
mm) of the bottom. These openings must communicate di­
rectly or by ducts with the outdoors or spaces (crawl or at­
tic) that freely communicate with the outdoors or indirectly
through vertical ducts. Each opening shall have a minimum
free area of 1 square inch (645 mm
kW) per hour of total input rating of all equipment in the en­
closure. See figures 3 and 4. When communicating with
the outdoors through horizontal ducts, each opening shall
have a minimum free area of 1 square inch (645 mm
2,000 Btu (.56 kW) per total input rating of all equipment in
the enclosure. See figure 5.
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 inches (75 mm). In calculating free
area, the blocking effect of louvers, grilles, or screens must
be considered. If the design and free area of protective cov­
ering 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.
Page 6
2
) per 4,000 Btu (1.17
2
) per

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