Carrier 58 Series - Manual (Page 3)

RETURN OR
SUPPLY AIR
VENT TO ROOF
I I
I I I
I
I I
i
T
D_L
12 IN MAX
I
-d
■= I so IN.
~ PER 1000
BTUH*
INTERIOR
HEATED
SPACE
-6IN MIN
(FRONT)
ISO IN
# per 1000
HTBTUH*
*-12 IN MAX
RETURN OR
SUPPLY AIR
J
*MINIMUM OPENING SIZE IS 100 SO IN
MAKEUP AIR
ISO IN
-PER 5000
BTUH FROM
OUTSIDE
(RETURN
AIR ONLY)
Fig. 1 — Upflow or Counterflow, Using Air
from Inside Building
I so IN. PER
2000 BTUH ^
USE ANY OF THE FOLLOWING COMBINATIONS
OF OPENINGS: ABB CSD D&E
*MINIMUM OPENING SIZE IS 100 SO IN
Fig. 2 — Upflow or Counterflow. Using Air
from Outside Building
bottom of the enclosure. These openings shall com­
municate directly, or by ducts, with outdoors.
See Fig. 2.
a. When communicating with the outdoors thru
horizontal ducts, each opening shall have mini­
mum free area of 1 sq in. per 2000 Btuh of total
input rating for all equipment in the enclosure. If
vertical ducts or openings with louvers and
grilles are used, each opening or duct shall have
a minimum free area of 1 sq in. per 4000 Btuh
of the total rated input of all equipment in the
enclosure.
b. When ducts are used, they shall be of the
same cross-sectional area as the free area of
the openings to which they connect. The mini­
mum dimension of rectangular air ducts shall not
be less than 3 inches.
Furnaces in Unconfined Spaces (Basements,
Large Equipment Rooms, etc.)
— If the uncon­
fined space is within a building of unusually tight
construction, air for combustion, ventilation, and
dilution of flue gases shall be obtained from out­
doors or from spaces freely communicating with the
outdoors. A permanent opening, or openings,
having a total free area of not less than 1 sq. in. per
5000 Btuh of total input rating for all equipment
shall be provided. A duct may be used to convey
makeup air from the outdoors and shall be of the
same cross-sectional area as the free area of the
openings to which it connects. The duct may be con­
nected to the eold air return of the heating system
only if it connects directly to outside air. The
minimum dimension of rectangular air ducts shall
be not less than 3 inches.
CAUTION: Return air must not be taken from
the room, unless an equal or greater amount of
air is supplied to the room. All duct connections
to the furnace must be airtight to avoid causing I
a “negative” pressure condition within the room.
Louvers and Grilles — In calculating the free area,
consideration shall be given to the blocking effect of
louvers, grilles, or screens protecting openings.
Screens used must not be smaller than I / 4-in. mesh.
If the free area thru a design of louver or grille is
known, it should be used in calculating the size
opening required to provide the free area specified.
If the design and free area is not known, assume 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 that provide
combustion and dilution air must be constructed so
they cannot be closed.