Table of Contents
Advertisement
Table 2 – Minimum Free Area Required for Each Combustion Air opening of Duct to Outdoors
FUR-
TWO HORIZONTAL DUCTS
NACE
(1 SQ. IN./2,000 BTUH) (1,100 SQ. MM/KW)
INPUT
Free Area of Opening
(BTUH)
and Duct (Sq.. In.)
44,000
22
66,000
33
88,000
44
110,000
55
132,000
66
154,000
77
FURNACE
WATER HEATER
110,000
+
30,000
66,000
+
40,000
88,000
+
30,000
Table 3 – Minimum Space Volumes for 100% Combustion, Ventilation, and Dilution from Indoors
OTHER THAN FAN---ASSISTED TOTAL
(1,000s 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
NP = Not Permitted
AIR FOR COMBUSTION AND
VENTILATION
Provisions for adequate combustion, ventilation, and dilution air
must be provided in accordance with:
S
U.S. Installations: Section 9.3 of the NFGC, Air for
Combustion and Ventilation and applicable provisions
of the local building codes.
S
Canadian Installations: Part 8 of the
CAN/CSA- -B149.1- -05, Venting Systems and Air
Supply for Appliances and all authorities having
jurisdiction.
CAUTION
!
FURNACE CORROSION HAZARD
Failure to follow this caution may result in furnace damage.
Air for combustion must not be contaminated by halogen
compounds, which include fluoride, chloride, bromide, and
iodide. These elements can corrode heat exchangers and
shorten furnace life. Air contaminants are found in aerosol
sprays, detergents, bleaches, cleaning solvents, salts, air
fresheners, and other household products.
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
7
8
9
10
10
EXAMPLES: Determining Free Area
TOTAL INPUT
=
(140,000 divided by 4,000)
=
(106,000 divided by 3,000)
=
(118,000 divided by 2,000)
40
50
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
Round Duct (in.
Dia)
14.7
5
22
6
29.3
7
36.7
7
44
8
51.3
9
=
35.0 Sq.. In. for each two Vertical Ducts or Open-
ings
=
35.3 Sq.. In. for a Single Duct or Opening
=
59.0 Sq.. In. for each of two Horizontal Ducts
FAN---ASSISTED TOTAL
(1,000s BTUH GAS INPUT RATE)
44
66
88
Space Volume (ft.3)
1,100
1,650
2,200
1,320
1,980
2,640
1,650
2,475
3,300
2,200
3,300
4,400
3,300
4,950
6,600
6,600
9,900
13,200
NP
NP
NP
!
CARBON MONOXIDE POISONING HAZARD
Failure to follow this warning could result in personal
injury or death.
The operation of exhaust fans, kitchen ventilation fans,
clothes dryers, attic exhaust fans or fireplaces could create a
NEGATIVE PRESSURE CONDITION at the furnace.
Make- -up air MUST be provided for the ventilation devices,
in addition to that required by the furnace. Refer to the
Carbon Monoxide Poisoning Hazard warning in the venting
section of these instructions to determine if an adequate
amount of make- -up air is available.
The requirements for combustion and ventilation air depend upon
whether or not the furnace is located in a space having a volume
of at least 50 cubic feet per 1,000 Btuh input rating for all gas
appliances installed in the space.
S
Spaces having less than 50 cubic feet per 1,000 Btuh
require the OUTDOOR COMBUSTION AIR
METHOD.
8
TWO OPENINGS OR VERTICAL DUCTS
(1 SQ. IN./4,000 BTUH) (550 SQ. MM/KW)
Free Area of Opening
Round Duct (In.
and Duct (Sq. In.)
11
16.5
22
27.5
33
38.5
110
132
2,750
3,300
3,300
3,960
4,125
4,950
5,500
6,600
8,250
9,900
16,500
19,800
NP
NP
WARNING
Dia)
4
5
6
6
7
8
154
3,850
4,620
5,775
7,700
11,550
23,100
NP
Advertisement
Table of Contents
