19
Table 1 – Minimum Free Area R equired 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
D u c t ---
Sq. In (Sq. mm)
Round Duct
In. (mm) Dia
Free Area of
Opening and
D u c t ---
Sq. In (Sq. mm)
Round Duct ---
In. (mm) Dia
Free Area of
Opening and
D u c t ---
Sq. In (mm)
Round Duct ---
In. (mm) Dia
40,000 20 (12903) 6 (152) 13.4 (8645) 5 (127) 10 (6451) 4 (102)
60,000 30 (19354) 7 (178) 20 (12903) 6 (152) 15 (9677) 5 (127)
80,000 40 (25806) 8 (203) 26.7 (17225) 6 (152) 20 (12903) 6 (152)
100,000 50 (32258) 8 (203) 33.4 (21548) 7 (178) 25 (16129) 6 (152)
120,000 60 (38709) 9 (229) 40 (25806) 8 (203) 30 (19354) 7 (178)
EXAMPLES: Determining Free Area
FURNACE WATER HEATER TOTAL INPUT
100,000 + 40,000 = (140,000 divided by 4,000) = 35.0 Sq. In. for each two Vertical Ducts or Openings
60,000 + 40,000 = (100,000 divided by 3,000) = 33.4 Sq. In. for a Single Duct or Opening
80,000 + 30,000 = (110,000 divided by 2,000) = 55.0 Sq. In. for each of two Horizontal Ducts
Table 2 – Minimum Space Vo lumes for 100% Combustion, Ventil atio n 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
SpaceVolumeFt
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
b. Not less than the sum of the areas of all vent
connectors in the space.
The opening shall commence within 12 in. (305 mm)
of the ceiling. Appliances in the space shall have
clearances of at least 1 in. (25 mm) from the sides and
back and 6 in. (153 mm) from the front. The 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 AirE NFPA & AGA
Standard and Known-Air-Infiltration Rate Methods
Indoor combustion air is permitted for combustion, ventilation,
and dilution, if the Standard or Known-Air-Infiltration Rate
Method is used.
CARBON MONOXIDE POISONING HAZARD
Failure to follow this warning could result 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.
!
WARNING
The Standard Method:
1. The space has no less volume than 50
3
ft. (1.4
3
M) (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).
The Known Air Infiltration Rate Method shall be used, if the
infiltration rate is known to be:
1. Less than 0.40 ACH and
2. Equal to or greater than 0.10 ACH
Infiltration rates greater than 0.60 ACH shall not be used. The
minimum required volume of the space varies with the number of
ACH and shall be determined per Table 2 or Equations 1 and 2.
Determine the minimum required volume for each appliance in
the space and add the volumes together to get the total minimum
required volume for the space.
Table 2 -- Minimum Space Volumes were determined by using the
following equations from the National Fuel Gas Code ANSI
Z223.1--2009/NFPA 54--2009,9.3.2.2:
353BAV
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