Lennox International Inc. o23v - Manual (Page 14)

Page 14
complete combustion which can result in sooting. Require-
ments for providing air for combustion and ventilation depend
largely on whether the furnace is installed in an uncon-
fined or confined space.
Unconfined Space
An unconfined space is an area such as a basement or
large equipment room with a volume greater than 50 cu-
bic feet (1.4 cubic meters) per 1,000 Btu (293 W) 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 proce-
dures outlined for using air from the outside for combus-
tion and ventilation.
Confined Space
A confined space is an area with volume less than 50 cu-
bic feet (1.4 cubic meters) per 1,000 Btu (293 W) per
hour of the combined 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 con-
fined 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.
Air from an Adjacent Space
If the confined space housing the furnace adjoins space
categorized as unconfined, air can be brought in by pro-
viding two permanent openings between the two
spaces. Each opening must have a minimum free area
of 1 square inch
(6.4 square centimeters) per 1,000 Btu
(293 W) per hour of the total input rating of all fuel−fired
equipment in the confined space. Each opening must
be at least 100 square inches (614.5 square centime-
ters). One opening shall be within 12" (305 mm) of the
top of the enclosure and one opening within 12" (305
mm) of the bottom (See figure 10).
EQUIPMENT IN CONFINED SPACE
ALL AIR FROM INSIDE
CHIMNEY OR
OIL VENT
WATER
HEATER
OPENINGS
(To Adjacent Room)
FIGURE 10
NOTE−Each opening shall have a free area of at least 1 square inch
(6.4 square centimeters) per 1,000 Btu (293 W) per hour of the total
input rating of all equipment in the enclosure, but not less than 100
square inches
(614.5 square centimeters).
OIL
FURNACE
Air from Outside
If air from outside is brought in for combustion and ven-
tilation, the confined space shall be provided with two
permanent openings. One opening shall be within 12"
(305 mm) of the top of the enclosure and one within 12"
(305 mm) of the bottom. These openings must communicate
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 1 square inch (6.4 square centimeters) per 4,000
Btu (1172 W) per hour of total input rating of all equipment in
the enclosure (See figures 11 and 12). When communicating
with the outdoors through horizontal ducts, each opening
shall have a minimum free area of 1 square inch (6.4
square centimeters) per 2,000 Btu (586 W) per total input
rating of all equipment in the enclosure (See figure 13).
EQUIPMENT IN CONFINED SPACE
ALL AIR FROM OUTSIDE
(Inlet Air from Crawl Space and
Outlet Air to Ventilated Attic)
NOTE−The inlet and outlet air openings shall each 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 equipment in the enclosure.
VENTILATION LOUVERS
(Each end of attic)
OUTLET
AIR WATER
HEATER
INLET
AIR
CHIMNEY
OR OIL
VENT
VENTILATION
LOUVERS
(For unheated
crawl space)
FIGURE 11
OIL
FURNACE