Air Ducts; General Requirements - Bryant 393AAV Installation, Start-Up, And Operating Instructions Manual

SUPPLY
AIR
INTERIOR
HEATED
SPACE
RETURN AIR
* Minimum opening size is 100 sq in. with
minimum dimensions of 3 in.
†
Minimum of 3 in. when type-B1 vent is used.
Fig. 3—Confined Space: Air for Combustion and Ventilation
from an Unconfined Indoor Space
b. If building is constructed unusually tight, a permanent
opening directly communicating with the outdoors shall
be provided. See item 2 below.
c. If furnace is installed on a raised platform to provide a
return-air plenum, and return air is taken directly from
hallway or space adjacent to furnace, all air for combus-
tion must come from outdoors.
2. Air from outside the structure requires 1 of the following
methods:
a. If combustion air is taken from outdoors through 2
vertical ducts, the openings and ducts MUST have at
least 1 sq in. of free area per 4000 Btuh of total input for
all equipment within the confined space. (See Fig. 4 and
Table 2.)
b. If combustion air is taken from outdoors through 2
horizontal ducts, the openings and ducts MUST have at
least 1 sq in. of free area per 2000 Btuh of total input for
all equipment within the confined space. (See Fig. 4 and
Table 2.)
c. If combustion air is taken from outdoors through a single
opening or duct (horizontal or vertical) commencing
within 12 in. of the top of the confined space, opening
and duct MUST have at least 1 sq in. of free area per
3000 Btuh of the total input for all equipment within the
confined space and not less than the sum of the areas of
VENT THROUGH ROOF
12" MAX
1 SQ IN.
PER 1000
BTUH * IN DOOR
OR WALL
UNCONFINED
SPACE
6" MIN
(FRONT) †
1 SQ IN.
PER 1000
BTUH * IN DOOR
OR WALL
12" MAX
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—5—
DUCTS
TO
OUTDOORS
12" MAX
1 SQ IN.
A
PER 2000
BTUH*
SUPPLY
AIR
DUCTS
TO
OUTDOORS
1 SQ IN.
B
PER 2000
BTUH*
12" MAX
RETURN AIR
*Minimum dimensions of 3 in.
NOTE: Use any of the following
combinations of openings:
A & B C & D D & E
Fig. 4—Confined Space: Air for Combustion and Ventilation
from Outdoors
all vent connectors in the confined space. (See Fig. 4 and
Table 2.) Equipment clearances to the structure shall be
at least 1 in. from the sides and back and 6 in. from the
front of the appliances.
When ducts are used, they must be of the same cross-sectional area
as the free area of the openings to which they connect. The
minimum dimension of ducts must not be less than 3 in. (See Fig.
4.)

AIR DUCTS

I. GENERAL REQUIREMENTS
The duct system should be designed and sized according to
accepted national standards such as those published by: Air
Conditioning Contractors Association (ACCA), Sheet Metal and
Air Conditioning Contractors National Association (SMACNA) or
American Society of Heating, Refrigerating and Air Conditioning
Engineers (ASHRAE). Or consult factory The Air Systems Design
Guidelines reference tables available from your local distributor.
The duct system should be sized to handle the required system
design airflow CFM at the design external static pressure.
When a furnace is installed so that the supply ducts carry air to
areas outside the space containing the furnace, the return air must
also be handled by a duct(s) sealed to the furnace casing and
terminating outside the space containing the furnace.
Secure ductwork with proper fasteners for type of ductwork used.
Seal supply- and return-duct connections to furnace with code
approved tape or duct sealer.
1 SQ IN.
PER 4000
BTUH*
D 12"
MAX
VENT
THROUGH
F
ROOF
1 SQ IN.
PER
4000
BTUH*
1 SQ IN.
PER
4000
BTUH*
E
G
12"
MAX
C
12" MAX
DUCT
1 SQ IN.
TO
PER 4000
OUTDOORS
BTUH*
F & G
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