Page 43
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 75mm (3 inches). In calculating free
area, the blocking effect of louvers, grilles, or screens
must be considered. If the design and free area of protec-
tive covering is not known for calculating the size opening
required, it may be assumed that wood louvers will have
20 to 25 percent 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.
FIGURE 36
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 645mm
2
per 1.17kW (one square inch per 4,000 Btu) per
hour of the total input rating of all equipment in the enclosure.
OUTLET
AIR
INLET
AIR
VENTILATION
LOUVERS
(For unheated
crawl space)
G61MPV
T
ROOF TERMINATED
EXHAUST PIPE
VENTILATION LOUVERS
(Each end of attic)
SIDE WALL
TERMINATED
EXHAUST PIPE
(ALTERNATE
LOCATION)
FIGURE 37
EQUIPMENT IN CONFINED SPACE − ALL AIR FROM OUTSIDE
(All Air Through Ventilated Attic)
OUTLET
AIR
VENTILATION LOUVERS
(Each end of attic)
INLET AIR
(Ends 12" above
bottom)
G61MPVT
ROOF TERMINATED
EXHAUST PIPE
SIDE WALL
TERMINATED
EXHAUST PIPE
(ALTERNATE
LOCATION)
NOTE−The inlet and outlet air openings shall each have a free area
of at least 645mm
2
per 1.17kW (one square inch per 4,000 Btu) per
hour of the total input rating of all equipment in the enclosure.
FIGURE 38
G61MPVT
EQUIPMENT IN CONFINED SPACE −
ALL AIR FROM OUTSIDE
OUTLET AIR
INLET AIR
NOTE−Each air duct opening shall have a free area of at least
645mm
2
per .59kW (one square inch per 2,000 Btu) per hour of the
total input rating of all equipment in the enclosure. If the equipment
room is located against an outside wall and the air openings com-
municate directly with the outdoors, each opening shall have a free
area of at least 645mm
2
per 1.17kW (one square inch per 4,000
Btu) per hour of the total input rating of all other equipment in the
enclosure.
ROOF TERMINATED
EXHAUST PIPE
SIDE WALL
TERMINATED
EXHAUST PIPE
(ALTERNATE
LOCATION)