Table
3
-
Minimum
Free
Area
Required
for
Each
Combustion
Air
Opening
or
Duct
to
Outdoors
TWO
HORIZONTAL
DUCTS
SINGLE
DUCT
OR
OPENING
NO
ea
Gore
(1
SQ.
IN./2,000
BTUH)
(1
SQ.
IN./3,000
BTUH)
(1
SQ.
IN./4,000
BTUH)
FURNACE
(1,100
SQ.
MM/KW)
(734
SQ.
MM/KW)
(550
sa
"MM/KW)
INPUT
:
(BTUH)
Free
Area
of
Free
Area
of
Free
Area
of
Opening
and
Round
Duct
Opening
and
Round
Duct
Opening
and
Round
Duct
Duct
In.
(mm)
Dia
Duct
In.
(mm)
Dia
Duct
In.
(mm)
Dia.
Sq.
In
(Sq.
mm)
Sq.
In
(Sq.
mm)
Sq.
In
(mm)
40,000*
20
(12904)
5
(127)
14
(8696)
5
(127)
10
(6452)
4
(102)
60,000
30
(19355)
6
(152)
20
(13043)
5
(127)
15
(9678)
5
(127)
80,000
40
(25807)
7
(178)
27
(17391)
6
(152)
20
(12904)
5
(127)
100,000
50
(82258)
8
(208)
34
(21739)
7
(178)
25
(16130)
6
(152)
120,000
60
(88709)
9
(229)
40
(26087)
7
(178)
30
(19355)
6
(152)
140,000*
70
(45161)
10
(254)
47
(80435)
8
(208)
35
(22581)
7
(178)
*Not
all
families
have
these
models.
EXAMPLES:
Determining
Free
Area
FURNACE
100,000
+
60,000
+
80,000
+
WATER
HEATER
30,000
40,000
30,000
TOTAL
INPUT
(130,000
divided
by
4,000)
=
(100,000
divided
by
3,000)
=
=
(110,000
divided
by
2,000)
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
Table
4
-
Minimum
Space
Volumes
for
100%
Combustion,
Ventilation
and
Dilution
Air
from
Outdoors
OTHER
THAN
FAN-ASSISTED
TOTAL
FAN-ASSISTED
TOTAL
(1,000’S
BTUH
GAS
INPUT
RATE)
(1,000’S
BTUH
GAS
INPUT
RATE)
ACH
30
|
40
|
50 40
|
60
|
80
|
100
|
120
|
140
Space
Volume
Ft?
(M°)
0.60
1,050 1,400
1,750
1,400 1,500
2,000 2,500 3,000 3,500
:
(29.7) (39.6) (49.5) (39.6) (42.5) (66.6) (70.8) (84.9) (99.1)
0.50
1,260 1,680
2,100
1,680
1,800
2,400 3,000 3,600 4,200
:
(35.6) (47.5) (69.4) (47.5) (61.0)
(67.9)
(84.9)
(101.9) (118.9)
0.40
1,575
2,100 2,625 2,100 2,250 3,000 3,750
4,500
5,250
:
(44.5) (69.4) (74.3) (69.4) (63.7) (84.9)
(106.1) (127.3)
(148.6)
0.30
2,100 2,800 3,500 2,800 3,000
4,000 5,000
6,000 7,000
:
(69.4) (79.2) (99.1) (79.2) (84.9)
(113.2) (141.5) (169.8) (198.1)
0.20
3,150
4,200 5,250 4,200 4,500
6,000
7,500
9,000
10,500
:
(89.1)
(118.9) (148.6) (118.9) (127.3) (169.8) (212.2)
(254.6)
(297.1)
0.10
6,300
8,400
10,500
8,400 9,000
12,000 15,000
18,000
21,000
:
(178.0)
(237.8) (297.3) (237.8)
(254.6)
(339.5) (424.4)
(609.2)
(694.1)
0.00
NP NP NP NP NP NP NP NP NP
NP
=
Not
Permitted
11
59SC2A
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