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820SB/821SB: Installation, Start–Up, Operating and Service and Maintenance Instructions
WARNING
!
CARBON MONOXIDE POISONING HAZARD
Failure to follow this warning could result in personal injury or death.
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.
Table 2 – Minimum Free Area Required for Each Combustion Air opening of Duct to Outdoors
TWO HORIZONTAL DUCTS
FURNACE
(1 SQ. IN./2,000 BTUH) (1,100 SQ. MM/KW)
INPUT
Free Area of
(BTUH)
Opening and Duct
Sq. In. (Sq. mm)
44,000
22 (14194)
66,000
33 (21290)
88,000
44 (28387)
110,000
55 (35484)
132,000
66 (42580)
154,000
77 (49677)
NOTE: Not all models have these sizes.
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
(1,000'S BTUH GAS INPUT RATE)
30
ACH
0.60
1,050 (29.7)
0.50
1,260 (35.6)
0.40
1,575 (44.5)
0.30
2,100 (59.4)
0.20
3,150 (89.1)
0.10
6,300 (178.3)
0.00
NP
NP = Not Permitted
NOTE: Not all models have these sizes.
The Standard Method
Use the Standard Method if:
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).
Use the Known Air Infiltration Rate Method 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 3
or Equations 1 and 2. Determine the minimum
Manufacturer reserves the right to change, at any time, specifications and designs without notice and without obligations.
(1 SQ. IN./3,000 BTUH) (734 SQ. MM/KW)
Round Duct Dia.
Opening and Duct
In. (mm)
Sq. In. (Sq. mm)
6 (152)
7 (178)
8 (203)
9 (229)
10 (254)
10 (254)
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 (39.6)
1,750 (49.5)
1,680 (47.5)
2,100 (59.4)
2,100 (59.4)
2,625 (74.3)
2,800 (79.2)
3,500 (99.1)
4,200 (118.9)
5,250 (148.6)
8,400 (237.8)
10,500 (297.3)
6,600 (186.8)
NP
NP
SINGLE DUCT OR OPENING
Free Area of
Round Duct Dia.
In. (mm)
14.7 (9484)
5 (127)
22 (14193)
6 (152)
29.3 (18903)
7 (178)
36.7 (23677)
7 (178)
44 (28387)
8 (203)
51.3 (33096)
9 (229)
=
=
=
FAN-ASSISTED TOTAL
(1,000'S BTUH GAS INPUT RATE)
44
66
3
3
Space Volume Ft
(M
)
1,100 (31.1)
1,650 (46.7)
2,200 (62.2)
1,320 (37.3)
1,980 (56.0)
2,640 (74.7)
1,650 (46.7)
2,475 (70.0)
3,300 (93.4)
2,200 (62.2)
3,300 (93.4)
4,400 (124.5)
3,300 (93.4)
4,950 (140.1)
6,600 (186.8)
9,900 (280.3)
13,200 (373.7)
NP
NP
required volume for each appliance in the space and add the volumes
together to get the total minimum required volume for the space.
Table 3
- Minimum Space Volumes were determined by using the
following equations from the National Fuel Gas Code ANSI
Z223.1/NFPA 54, 9.3.2.2:
1. For other than fan-assisted appliances, such as a draft
hood-equipped water heater:
2. For fan-assisted appliances such as this furnace:
8
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)
11 (7096)
16.5 (10645)
22 (14193)
27.5 (17742)
33 (21290)
38.5 (24839)
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
88
110
132
2,750 (77.8)
3,300 (93.4)
3,300 (93.4)
3,960 (112.1)
4,125 (116.8)
4,950 (140.1)
5,500 (155.7)
6,600 (186.8)
8,250 (233.6)
9,900 (280.3)
16,500 (467.2)
19,800 (560.6)
NP
NP
NP
Round Duct Dia.
In. (mm)
4 (102)
5 (127)
6 (152)
6 (152)
7 (178)
8 (203)
154
3,850 (109.0)
4,620 (130.8)
5,775 (163.5)
7,700 (218.0)
11,550 (327.0)
23,100 (654.1)
NP
A04002
A04003
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