Bryant 355AAV Installation Instructions Manual page 19

Table 1 – Minimum Free Area Required for Each Combustion Air Opening or Duct to Outdoors
FURNACE
TWO HORIZONTAL DUCTS
INPUT
(1 SQ. IN./2,000 BTUH) (1,100 SQ. MM/KW)
(BTUH)
Free Area of Opening
and Duct (Sq. In.)
40,000 20
60,000 30
80,000 40
100,000 50
120,000 60
FURNACE WATER HEATER
100,000
+ 40,000
60,000 + 40,000
80,000 + 30,000
Table 2 – Minimum Space Volumes for 100% Combustion, Ventilation and Dilution Air from Outdoors
OTHER THAN FAN---ASSISTED TOTAL
(1,000'S BTUH GAS INPUT RATE)
ACH
30
0.60
1,050
0.50 1,260
0.40 1,575
0.30 2,100
0.20 3,150
0.10 6,300
0.00 NP
b. Combining spaces on same floor level. Each opening
shall have free area of at least 1 in.
2
mm /kW) of the total input rating of all gas appliances
in the space, but not less than 100 in.
opening shall commence within 12" (300 mm) of the
ceiling and the second opening shall commence within
12" (300 mm) of the floor. The minimum dimension of
air openings shall be at least 3 in. (80 mm). (See Fig.
20.)
c. Combining space on different floor levels. The volumes
of spaces on different floor levels shall be considered as
communicating spaces if connected by one or more
permanent openings in doors or floors having free area
2
of at least 2 in. /1,000 Btuh (4,400 mm
input rating of all gas appliances.
2. An attic or crawlspace may be considered a space that freely
communicates with the outdoors provided there are
adequate permanent ventilation openings directly to
outdoors having free area of at least 1- -in.
total input rating for all gas appliances in the space.
3. In spaces that use the Indoor Combustion Air Method,
infiltration should be adequate to provide air for
combustion, permanent ventilation and dilution of flue
gases. However, in buildings with unusually tight
construction, additional air MUST be provided using the
methods described in the Outdoor Combustion Air
Method section.
SINGLE DUCT OR OPENING
(1 SQ. IN./3,000 BTUH) (734 SQ. MM/KW)
Round Duct (in. Free Area of Opening
Dia) and Duct (sq In.)
6 13.4
7 20
8 26.7
8 33.4
9 40
EXAMPLES: Determining Free Area
TOTAL INPUT
= (140,000 divided by 4,000)
= (100,000 divided by 3,000)
= (110,000 divided by 2,000)
40 50
Space Volume (ft3)
1,400 1,750
1,680 2,100
2,100 2,625
2,800 3,500
4,200 5,250
8,400 10,500
NP NP
2
/1,000 Btuh (2,000
2 2
(0.06 m ). One
2
/kW) of total
2
/4,000 Btuh of
TWO OPENINGS OR VERTICAL DUCTS
(1 SQ. IN./4,000 BTUH) (550 SQ. MM/KW)
Round Duct (in. Free Area of Opening
Dia)
5
6
6
7
8
= 35.0 Sq. In. for each two Vertical Ducts or Openings
= 33.4 Sq. In. for a Single Duct or Opening
= 55.0 Sq. In. for each of two Horizontal Ducts
FAN---ASSISTED TOTAL
(1000'S BTUH GAS INPUT RATE)
40 60
1,000 1,500
1,200 1,800
1,500 2,250
2,000 3,000
3,000 4,500
6,000 9,000
NP NP
Unusually tight construction is defined as
Construction with:
a. Walls and ceilings exposed to the outdoors have a
continuous, sealed vapor barrier. Openings are gasketed
or sealed and
b. Doors and openable windows are weatherstripped and
c. Other openings are caulked or sealed. These include
joints around window and door frames, between sole
plates and floors, between wall- -ceiling joints, between
wall panels, at penetrations for plumbing, electrical and
gas lines, etc.
NOTE: In determining the free area of an opening, the blocking
effect of the louvers, grilles, and screens must be considered. If the
free area of a louver or grille design is unknown, it may be
assumed that wood louvers have a 20 percent free area, and metal
louvers or grilles have a 60 percent free area. Screens, when used,
must not be smaller than 1/4- -in. (6 mm) mesh. Louvers and grilles
must be constructed so they cannot be closed.
19
Round Duct (In.
and Duct (Sq In.) Dia)
10 4
15 5
20 6
25 6
30 7
80 100 120
2,000 2,500 3,000
2,400 3,000 3,600
3,000 3,750 4,500
4,000 5,000 6,000
6,000 7,500 9,000
12,000 15,000 18,000
NP NP NP