Carrier 120/C Series Installation, Start-Up, Operating And Service And Maintenance Instructions page 8

Table 2–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.)
44,000 22
66,000 33
88,000 44
110,000 55
132,000 66
154,000 77
EXAMPLES: Determining Free Area
FURNACE WATER HEATER
110,000 +
66,000 +
88,000 +
Table 3–Minimum Space Volumes for 100% Combustion, Ventilation, and
OTHER THAN FAN-ASSISTED TOTAL
(1,000'S 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
2. Fig. 7 illustrates how to provide TWO OUTDOOR OPEN-
INGS, one inlet and one outlet combustion and ventilation air
opening, to the outdoors.
a. One opening MUST commence within 12" (300 mm) of
the ceiling and the second opening MUST commence
within 12" (300 mm) of the floor.
b. Size openings and ducts per Fig. 7 and Table 2.
c. TWO HORIZONTAL DUCTS require 1 square inch of
free area per 2,000 Btuh (1,100 mm
input for all gas appliances in the space per Fig. 7 and Table
2.
d. TWO OPENINGS OR VERTICAL DUCTS require 1
square inch of free area per 4,000 Btuh (550 mm
combined input of all gas appliances in the space per Fig.
7 and Table 2.
3. ONE OUTDOOR OPENING requires:
a. 1 square inch of free area per 3,000 Btuh (734 mm
for combined input of all gas appliances in the space per
Table 2 and
b. Not less than the sum of the areas of all vent connectors in
the space.
The opening shall commence within 12" (300 mm) of the ceiling.
Appliances in the space shall have clearances of at least 1" (25
mm) from the sides and back and 6" (150 mm) from the front. The
(1 SQ. IN./3,000 BTUH) (734 SQ. MM/KW)
Round Duct
(in. Dia)
6
7
8
9
10
10
TOTAL INPUT
30,000 = (140,000 divided by 4,000)
40,000 = (106,000 divided by 3,000)
30,000 = (118,000 divided by 2,000)
Dilution from Indoors
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
2
/kW) of combined
2
SINGLE DUCT OR OPENING
Free Area of
Round Duct
Opening and Duct
(in. Dia)
(sq In.)
14.7
22
29.3
36.7
44
51.3
=
=
=
(1,000'S BTUH GAS INPUT RATE)
44 66
3
Space Volume (ft )
1,100 1,650
1,320 1,980
1,650 2,475
2,200 3,300
3,300 4,950
6,600 9,900
NP NP
opening shall directly communicate with the outdoors or shall
communicate through a vertical or horizontal duct to the outdoors
or spaces (crawl or attic) that freely communicate with the
outdoors.
Indoor Combustion Air© NFPA & AGA
Standard and Known-Air-Infiltration Rate Methods
Indoor air is permitted for combustion, ventilation, and dilution,
if the Standard or Known-Air-Infiltration Method is used.
CARBON MONOXIDE POISONING HAZARD
Failure to follow this warning could result
/kW) for in death and/or personal injury.
Many homes require air to be supplied from outdoors for
furnace combustion, ventilation, and dilution of flue gases.
The furnace combustion air supply must be provided in
accordance with this instruction manual.
2
/kW)
The Standard Method:
1. The space has no less volume than 50 cubic feet per 1,000
Btuh of the maximum input ratings for all gas appliances
installed in the space and
2. The air infiltration rate is not known to be less than 0.40 air
changes per hour (ACH).
8
TWO OPENINGS OR VERTICAL DUCTS
(1 SQ. IN./4,000 BTUH) (550 SQ. MM/KW)
Free Area of
Opening and Duct
(Sq In.)
5 11
6 16.5
7 22
7 27.5
8 33
9 38.5
35.0 Sq. In. for each two Vertical Ducts or Openings
35.3 Sq. In. for a Single Duct or Opening
59.0 Sq. In. for each of two Horizontal Ducts
FAN-ASSISTED TOTAL
88 110
2,200 2,750
2,640 3,300
3,300 4,125
4,400 5,500
6,600 8,250
13,200 16,500
NP NP
Round Duct
(In. Dia)
4
5
6
6
7
8
132 154
3,300 3,850
3,960 4,620
4,950 5,775
6,600 7,700
9,900 11,550
19,800 23,100
NP NP