Minimum Free Area Required; Minimum Space Volumes - Bryant 912SC Installation, Start-Up, Operating And Service And Maintenance Instructions

Table 3 – Minimum Free Area Required for Each Combustion Air Opening or Duct to Outdoors
TWO HORIZONTAL DUCTS
(1 SQ. IN./2,000 BTUH)
(1,100 SQ. MM/KW)
FURNACE
INPUT
Free Area of
(BTUH)
Opening and
Duct
Sq. In (Sq. mm)
40,000* 20 (12904)
60,000
30 (19355)
80,000 40 (25807)
100,000 50 (32258)
120,000 60 (38709)
140,000* 70 (45161)
*Not all families have these models.
FURNACE WATER HEATER
100,000 + 30,000
60,000 + 40,000
80,000 + 30,000
Table 4 – Minimum Space Volumes for 100% Combustion, Ventilation and Dilution Air from Outdoors
OTHER THAN FAN-ASSISTED TOTAL
(1,000'S BTUH GAS INPUT RATE)
30
ACH
1,050
0.60
(29.7)
1,260
0.50
(35.6)
1,575
0.40
(44.5)
2,100
0.30
(59.4)
3,150
0.20
(89.1) (118.9)
6,300
0.10
(178.0) (237.8)
0.00 NP
NP = Not Permitted
Round Duct
In. (mm) Dia
Sq. In (Sq. mm)
5 (127)
6 (152)
7 (178)
8 (203)
9 (229)
10 (254)
EXAMPLES: Determining Free Area
TOTAL INPUT
= (130,000 divided by 4,000)
= (100,000 divided by 3,000)
= (110,000 divided by 2,000)
40 50
1,400 1,750 1,400
(39.6) (49.5) (39.6)
1,680 2,100 1,680
(47.5) (59.4) (47.5)
2,100 2,625 2,100
(59.4) (74.3) (59.4)
2,800 3,500 2,800
(79.2) (99.1) (79.2)
4,200 5,250 4,200
(148.6) (118.9)
8,400 10,500 8,400
(297.3) (237.8)
NP NP
SINGLE DUCT OR OPENING
(1 SQ. IN./3,000 BTUH)
(734 SQ. MM/KW)
Free Area of
Round Duct
Opening and
In. (mm) Dia
Duct
14 (8696) 5 (127)
20 (13043) 5 (127)
27 (17391) 6 (152)
34 (21739) 7 (178)
40 (26087) 7 (178)
47 (30435) 8 (203)
= 32.5 Sq. In. for each two Vertical Ducts or Openings
= 33.3 Sq. In. for each Single Duct or Opening
= 55.0 Sq. In. for each two Horizontal Ducts
FAN-ASSISTED TOTAL
(1,000'S BTUH GAS INPUT RATE)
40 60 80
3 3
Space Volume Ft (M )
1,500 2,000
(42.5) (56.6)
1,800 2,400
(51.0) (67.9)
2,250 3,000
(63.7) (84.9)
3,000 4,000
(84.9) (113.2)
4,500 6,000
(127.3) (169.8)
9,000 12,000
(254.6) (339.5)
NP NP NP
11
TWO OPENINGS OR
VERTICAL DUCTS
(1 SQ. IN./4,000 BTUH)
(550 SQ. MM/KW)
Free Area of
Round Duct
Opening and
In. (mm) Dia.
Duct
Sq. In (mm)
10 (6452) 4 (102)
15 (9678) 5 (127)
20 (12904) 5 (127)
25 (16130) 6 (152)
30 (19355) 6 (152)
35 (22581) 7 (178)
100 120 140
2,500 3,000 3,500
(70.8) (84.9) (99.1)
3,000 3,600 4,200
(84.9) (101.9) (118.9)
3,750 4,500 5,250
(106.1) (127.3) (148.6)
5,000 6,000 7,000
(141.5) (169.8) (198.1)
7,500 9,000 10,500
(212.2) (254.6) (297.1)
15,000 18,000 21,000
(424.4) (509.2) (594.1)
NP NP NP