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When ducts are used, they must be of the same cross-sectional area
as the free area of the openings to which they connect. The
minimum dimension of ducts must not be less than 3 in. (See Fig.
4.)
AIR DUCTS
Step 1—General Requirements
The duct system should be designed and sized according to
accepted national standards such as those published by: Air
Conditioning Contractors Association (ACCA), Sheet Metal and
Air Conditioning Contractors National Association (SMACNA) or
American Society of Heating, Refrigerating and Air Conditioning
Engineers (ASHRAE). Or consult factory The Air Systems Design
Guidelines reference tables available from your local distributor.
The duct system should be sized to handle the required system
design airflow CFM at the design external static pressure.
When a furnace is installed so that the supply ducts carry air to
areas outside the space containing the furnace, the return air must
also be handled by a duct(s) sealed to the furnace casing and
terminating outside the space containing the furnace.
Secure ductwork with proper fasteners for type of ductwork used.
Seal supply- and return-duct connections to furnace with code
approved tape or duct sealer.
Flexible connections should be used between ductwork and
furnace to prevent transmission of vibration. Ductwork passing
through unconditioned space should be insulated to enhance
system performance. When air conditioning is used, a vapor
barrier is recommended.
Maintain a 1-in. clearance from combustible materials to supply air
ductwork for a distance of 36 in. horizontally from the furnace. See
NFPA 90B or local code for further requirements.
Step 2—Ductwork Acoustical Treatment
Metal duct systems that do not have a 90 degree elbow and 10 ft
of main duct to the first branch take-off may require internal
acoustical lining. As an alternative, fibrous ductwork may be used
if constructed and installed in accordance with the latest edition of
SMACNA construction standard on fibrous glass ducts. Both
acoustical lining and fibrous ductwork shall comply with NFPA
90B as tested by UL Standard 181 for Class 1 Rigid air ducts.
Step 3—Supply Air Connections
Connect supply-air duct to 3/4-in. flange on furnace supply-air
outlet. The supply-air duct attachment must ONLY be connected
to furnace supply-/outlet-air duct flanges or air conditioning coil
casing (when used). DO NOT cut main furnace casing to attach
supply side air duct, humidifier, or other accessories. All accesso-
ries MUST be connected external to furnace main casing.
Step 4—Return Air Connections
Never connect return-air ducts to the back of the furnace. A
failure to follow this warning can cause a fire, personal injury,
or death.
The return-air duct must be connected to bottom , sides (left or
right), or a combination of bottom and side(s) of main furnace
casing as shown in Fig. 1. Bypass humidifier may be attached into
unused side return air portion of the furnace casing. DO NOT
connect any portion of return-air duct to back of furnace casing.
Step 5—Filter Arrangement
The factory-supplied filter(s) is shipped in the blower compart-
ment. Determine location for the filter and relocate filter retaining
wire if necessary. See Fig. 5 for side return application and Fig. 6
for bottom return application. See Table 3 to determine correct
filter size for desired filter location. Table 3 indicates filter size,
location, and quantity shipped with the furnace.
For bottom air-return applications, filter may need to be cut to fit
some furnace casing widths. A bottom closure panel is factory
installed in the bottom of the furnace. When bottom return inlet is
desired, remove and discard the bottom closure panel. Two sets of
hardware are needed for furnaces in 24-1/2-in. wide casings using
2 filters for bottom return. All hardware is provided for filter
installation.
NOTE:
Furnaces with a 17-1/2-in. wide casing require an addi-
tional procedure when locating the filter for bottom return-air
application. Field fabricate a sheet metal filler strip 1 X 3 X 24-1/2
in. and install it along side of the filter as shown in Fig. 6. Drive
2 screws through the casing side and into the filler strip to secure
Table 2—Minimum Free Area Of Combustion Air Opening*
58WAV
FURNACE
INPUT
(BTUH)
AIR FROM INDOOR
UNCONFINED SPACE
OUTDOOR AIR THROUGH
VERTICAL DUCTS
OUTDOOR AIR THROUGH
HORIZONTAL DUCTS
OUTDOOR AIR THROUGH
SINGLE DUCT
Free Area
of Opening
(Sq In.)
Free Area of
Opening and Duct
(Sq In.)
Round
Pipe
(In. Dia)
Free Area of
Opening and Duct
(Sq In.)
Round
Pipe
(In. Dia)
Free Area of
Opening and Duct
(Sq In.)
Round
Pipe
(In. Dia)
44,000
100
11.0
4
22.0
6
14.67
5
66,000
100
16.5
5
33.0
7
22.00
6
88,000
100
22.0
6
44.0
8
29.33
7
110,000
110
27.5
6
55.0
9
36.67
7
132,000
132
33.0
7
66.0
10
44.00
8
154,000
154
38.5
8
77.0
10
51.33
9
* Free area shall be equal to or greater than the sum of the areas of all vent connectors in the confined space. Opening area must be increased if other gas appliances
in the space require combustion air.
Fig. 5—Side Filter Arrangement
(Control Removed for Clarity)
A93045
FILTER
RETAINER
WASHABLE
FILTER
6
Summary of Contents for WEATHERMAKER 8000 58WAV
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