Lennox ML180UHA Installation Instructions Manual page 6

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 305 mm (12 inches) of the
top of the enclosure and one opening within 305 mm (12
inches) 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 indirect­
ly through vertical ducts. Each opening shall have a mini­
mum free area of 645 mm
(4,000 Btu) per hour of total input rating of all equipment in
the enclosure. See figures 2 and 3. When communicating
with the outdoors through horizontal ducts, each opening
shall have a minimum free area of 645 mm
per .56 kW (2,000 Btu) per total input rating of all equipment
CHIMNEY OR
FURNACE
(For unheated crawl space)
NOTE-The inlet and outlet air openings shall each have a free area of at least 645 mm
inch) per 1.17 kW (4,000 Btu) per hour of the total input rating of all equipment in the enclosure.
2
(1 square inch) per 1.17 kW
2
(1 square inch)
GAS VENT
VENTILATION LOUVERS
(Each end of attic)
VENTILATION
LOUVERS
in the enclosure. See figure 4.
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 75 mm (3 inches). 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.
EQUIPMENT IN CONFINED SPACE
ALL AIR FROM OUTSIDE
(Inlet Air from Crawlspace and Outlet Air to Ventilated Attic)
OUTLET
AIR
WATER
HEATER
INLET
AIR
2
(one square
FIGURE 2
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