INSTALLATION INSTRUCTIONS
Gas Furnace: N9MSE
440 01 4103 03
11
Specifications subject to change without notice.
Figure 7
Air for Combustion, Ventilation,
and Dilution from Indoors
* Minimum opening size is 100 sq in. (64516 sq. mm) with
minimum dimensions of 3‐in. (76mm)
Minimum of 3‐in. (76mm) when type‐B1 vent is used.
L12F013
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
.
4. 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.
Combination of Indoor and Outdoor Air
1. Indoor openings shall comply with the
Indoor
Combustion Air
Method below and,
2. Outdoor openings shall be located as required in the
Outdoor Combustion Air
Method mentioned previously
and,
3. Outdoor openings shall be sized as follows:
a. Calculate the Ratio of all Indoor Space volume
divided by required volume for
Indoor Combustion
Air
Method.
b. Outdoor opening size reduction
Factor
is one minus
the
Ratio
in a. above.
c. Minimum size of Outdoor openings shall be the size
required in
Outdoor Combustion Air
Method above
multiplied by reduction
Factor
in b. above. The
minimum dimension of air openings shall be not less
than 3-in. (80 mm).
Table 3
Minimum Free Area Required for Each Combustion Air Opening or Duct to Outdoors
FURNACE
INPUT
(BTUH)
TWO HORIZONTAL DUCTS
(1 SQ. IN./2,000 BTUH)
(1,100 SQ. MM/KW)
SINGLE DUCT OR OPENING
(1 SQ. IN./3,000 BTUH)
(734 SQ. MM/KW)
TWO OPENINGS OR
VERTICAL DUCTS
(1 SQ. IN./4,000 BTUH)
(550 SQ. MM/KW)
Free Area of
Opening and Duct
Sq. In (Sq. mm)
Round
Duct
In. (mm)
Dia
Free Area of Open-
ing and Duct
Sq. In (Sq. mm)
Round
Duct
In. (mm)
Dia
Free Area of Open-
ing and Duct
Sq. In (mm)
Round Duct
In. (mm)
Dia.
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 (32258)
8 (203)
34 (21739)
7 (178)
25 (16130)
6 (152)
120,000
60 (38709)
9 (229)
40 (26087)
7 (178)
30 (19355)
6 (152)
140,000
70 (45161)
10 (254)
47 (30435)
8 (203)
35 (22581)
7 (178)
EXAMPLE
:
Determining Free Area
FURNACE
WATER HEATER
TOTAL INPUT
100,000
+
30,000
= (130,000 divided by 4,000)
= 32.5 Sq. In. for each two Vertical Ducts or Openings
60,000
+
40,000
= (100,000 divided by 3,000)
= 33.3 Sq. In. for each Single Duct or Opening
80,000
+
30,000
= (110,000 divided by 2,000)
= 55.0 Sq. In. for each two Horizontal Ducts
