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Table 1 – 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. (mm)
Round Duct
Dia.
In. (mm)
Free Area of Opening
and Duct
Sq. In (mm)
Round Duct
Dia.
In. (mm)
Free Area of Opening
and Duct
Sq. In (mm)
Round Duct
Dia.
In. (mm)
44,000
22 (14194)
6 (152)
14.7 (9494)
5 (127)
11 (7097)
4 (102)
66,000
33 (21290)
7 (178)
22 (14193)
6 (152)
16.5 (10645)
5 (127)
88,000
44 (28387)
8 (203)
29.3 (18903)
7 (178)
22 (14193)
6 (152)
110,000
55 (35484)
9 (229)
36.7 (23677)
7 (178)
27.5 (17741)
6 (152)
132,000
66 (42581)
10 (254)
44 (28387)
8 (203)
33 (21290)
7 (198)
154,000
77 (49677)
10 (254)
51.3 (33096)
9 (229)
38.5 (24838)
8 (203)
EXAMPLE
:
Determining Free Area
FURNACE
WATER HEATER
TOTAL INPUT
110,000
+
30,000
= (140,000 divided by 4,000)
=
35.0 Sq. In. for each two Vertical Ducts or Openings
66,000
+
40,000
= (106,000 divided by 3,000)
=
35.3 Sq. In. for a Single Duct or Opening
88,000
+
30,000
= (118,000 divided by 2,000)
=
59.0 Sq. In. for each of two Horizontal Ducts
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)
FAN-ASSISTED TOTAL
(1,000’S BTUH GAS INPUT RATE)
ACH
30
40
50
44
66
88
110
132
154
Space Volume Ft
3
(M
3
)
0.60
1,050
(29.7)
1,400
(39.6)
1,750
(49.5)
1,100
(31.1)
1,650
(46.7)
2,200
(62.2)
2,750
(77.8)
3,300
(93.4)
3,850
(109.0)
0.50
1,260
(35.6)
1,680
(47.5)
2,100
(59.4)
1,320
(37.3)
1,980
(56.0)
2,640
(74.7)
3,300
(93.4)
3,960
(112.1)
4,620
(130.8)
0.40
1,575
(44.5)
2,100
(59.4)
2,625
(74.3)
1,650
(46.7)
2,475
(70.0)
3,300
(93.4)
4,125
(116.8)
4,950
(140.1)
5,775
(163.5)
0.30
2,100
(59.4)
2,800
(79.2)
3,500
(99.1)
2,200
(62.2)
3,300
(93.4)
4,400
(124.5)
5,500
(155.7)
6,600
(186.8)
7,700
(218.0)
0.20
3,150
(89.1)
4,200
(118.9)
5,250
(148.6)
3,300
(93.4)
4,950
(140.1)
6,600
(186.8)
8,250
(233.6)
9,900
(280.3)
11,550
(327.0)
0.10
6,300
(178.3)
8,400
(237.8)
10,500
(297.3)
6,600
(186.8)
9,900
(280.3)
13,200
(373.7)
16,500
(467.2)
19,800
(560.6)
23,100
(654.1)
0.00
NP
NP
NP
NP
NP
NP
NP
NP
NP
NON-DIRECT VENT (1-PIPE) APPLICATION
UNIT DAMAGE HAZARD
Failure to follow this caution may result in intermittent
unit operation.
Do not install furnace in a corrosive or contaminated
atmosphere. Make sure all combustion and circulating air
requirements are met.
CAUTION
!
Refer to the AIR FOR COMBUSTION AND VENTILATION
section for details.
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 NFPA 54/ANSI
Z223.1--2006, 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.
FURNACE CORROSION HAZARD
Failure to follow this warning could result in reduced furnace
component life.
Air for combustion must not be contaminated by halogen
compounds, which include fluoride, chloride, bromide, and
iodide. These elements could 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.
!
WARNING
The following types of furnace installations may require
OUTDOOR AIR for combustion due to chemical exposures:
S
Commercial buildings
S
Buildings with indoor pools
S
Laundry rooms
S
Hobby or craft rooms, and
S
Chemical storage areas
If air is exposed to the following substances, it should not be
used for combustion air, and outdoor air may be required
for combustion:
S
Permanent wave solutions
S
Chlorinated waxes and cleaners
58MCB
