Goodman GMN SERIES Installation & Operating Instructions Manual page 9

1.) The passageways that supply combustion/ventilation air must not be obstructed to prevent flow of air to the mechanical
room. Extra care is to be used to prevent blockage of the ducts due to insulation, as may occur in an attic.
2.) As outlined in the Figures 1, 2, and 3 the size of the combustion and ventilation air ducts depend upon where the source
of the air is located. It is important to note that all sizes are to be regarded as "free area" and any obstruction such as an
inlet or outlet grille must be made up for in the size of the openings. No screen may be used at the outlet or inlet of these
ducts which are smaller than 1/4" mesh. Any grille used must be non-moveable fixed grilles. The user should be informed
not to block or in any manner restrict these openings.
Figure 1. Shows air taken from the living area must be from two (2) permanent openings with each opening having a minimum
of 1 square inch per 1000 BTUH/ of total gas burning equipment. With a minimum of 100 square inches, one opening must
be located within 12 inches from the top of the enclosure, and the other opening is to be located within 12 inches of the bottom
of the enclosure.
Note: The openings must not originate in a bedroom, bathroom or any room which may be commonly closed.
Figure 2. Shows the combustion/ventilation air supplied to the mechanical room from the outside via horizontal ducts are
to be a minimum of 1 square inch per 2000 BTUH of total gas burning equipment.
Figure 3. Demonstrates combustion/ventilation air origination from a ventilated attic or crawl space. This type of installation
requires a minimum of 1 square inch per 4000 BTUH of total gas burning equipment contained in the enclosure. For
acceptable intake and exhaust duct location please refer to Figure 3.
3.) The combustion and ventilation air openings must be of equal size and sized appropriately.
Use the table below as a guide:
TOTAL
APPLIANCE INPUT
60,000
80,000
100,000
120,000
The preceding table shows the combustion/ventilation air openings based upon the furnace only. If additional gas fired
equipment is installed in the mechanical room use the following work sheet to determine the combustion/ventilation air duct
size requirements:
Total Appliance Input (Furnace + all other gas fired equipment) =
BTUH per square inch requirement - 1000, 2000 or 4000 (see figures 1 through 3) =
Rectangular duct size = Total Appliance Input / BTUH per square inch requirement =
4.) When the installation is in an unconfined space in buildings of conventional frame, brick, or stone construction, normal
infiltration found in these types of construction should be adequate to provide the necessary air for combustion and ventilation.
If the unconfined space is within a building of unusually tight construction, provisions for combustion and outlet air must be
provided as shown in Figure 3.
5.) No dimension of a rectangular duct used to carry combustion or ventilation air shall be less than 3".
6.) Do not locate the combustion air source in an area which may contain corrosive chemicals such as a chlorine, sulphur,
fluorine, laundry cleaners or other damaging chemicals.
7.) If unit is installed near an exhaust fan, sufficient combustion and ventilation must be provided to prevent the exhaust fan
from creating a negative pressure in the room.
8.) Combustion Air must not be obtained from a bedroom or bathroom.
CONSULT LOCAL CODES FOR SPECIAL OR ADDITIONAL REQUIREMENTS.
1000 BTUH / SQ. INCH
RD. PIPE RECT. DUCT
11" DIA. 100 SQ. IN.
11" DIA. 100 SQ. IN.
11" DIA. 100 SQ. IN.
13" DIA. 120 SQ. IN.
2000 BTUH / SQ. INCH
RD. PIPE RECT. DUCT
7" DIA. 30 SQ. IN.
8" DIA. 40 SQ. IN.
8" DIA. 50 SQ. IN.
9" DIA. 60 SQ. IN.
9
4000 BTUH / SQ. INCH
RD. PIPE RECT.DUCT
5" DIA. 15 SQ. IN.
5" DIA. 20 SQ. IN.
6" DIA. 25 SQ. IN.
7" DIA. 30 SQ. IN.