Lennox G61MPVT-36B-070 Installation Instructions Manual page 42

Unconfined Space
An unconfined space is an area such as a basement or
large equipment room with a volume greater than 1.42 m
per .29 kW (50 cubic feet per 1,000Btu) per hour of the
combined input rating of all appliances installed in that
space. This space also includes adjacent rooms which are
not separated by a door. Though an area may appear to be
unconfined, it might be necessary to bring in outdoor air for
combustion if the structure does not provide enough air by
infiltration. If the furnace is located in a building of tight
construction with weather stripping and caulking around
the windows and doors, follow the procedures in the air
from outside section.
Confined Space
A confined space is an area with a volume less than 1.42 m
per .29 kW (50 cubic feet per 1,000Btu) per hour of the com−
bined input rating of all appliances installed in that space. This
definition includes furnace closets or small equipment rooms.
When the furnace is installed so that supply ducts carry air
circulated by the furnace to areas outside the space con-
taining the furnace, the return air must be handled by ducts
which are sealed to the furnace casing and which terminate
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 ei-
ther from inside the building or from outside.
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
2
645 mm per .29 kW (1 square inch per 1,000Btu) per hour
of total input rating of all gas−fired equipment in the con-
fined space. Each opening must be at least 64516 mm
(100 square inches). One opening shall be within 305 mm
3
(12 inches) of the top of the enclosure and one opening
within 305 mm (12 inches) of the bottom.
EQUIPMENT IN CONFINED SPACE − ALL AIR FROM INSIDE
ROOF TERMINATED
EXHAUST PIPE
SIDE WALL
TERMINATED EX-
3
HAUST PIPE (ALTER-
NATE LOCATION)
NOTE − Each opening shall have a free area of at least 645mm
.29kW (one square inch per 1,000 Btu) per hour of the total input rat-
ing of all equipment in the enclosure, but not less than 64516mm.
(100 square inches).
Air from Outside
If air from outside is brought in for combustion and ventila-
tion, the confined space shall be provided with two perma-
nent openings. One opening shall be within 305mm (12
inches) of the top of the enclosure and one within 305mm
(12 inches) of the bottom. These openings must commu-
nicate directly or by ducts with the outdoors or spaces
(crawl or attic) that freely communicate with the outdoors
or indirectly through vertical ducts. Each opening shall
have a minimum free area of 645mm
square inch per 4,000 Btu) per hour of total input rating of
all equipment in the enclosure. When communicating with
the outdoors through horizontal ducts, each opening shall
have a minimum free area of 645mm
square inch per 2,000 Btu) per total input rating of all
equipment in the enclosure.
Page 42
OPENINGS
(To Adjacent
Unconfined
Space)
G61MPV
T
FIGURE 35
2
per 1.17kW (1
2
per .59kW (1
2
2
per
2