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NOMINAL IRON PIPE SIZE (IN.)
1/2
3/4
1
1 1/4
1 1/2
*Capacity of pipe in cu. ft. of gas per hr. for gas pressure of 0.5 psig or less. Pressure drop of 0.5-in. wg (based on a 0.60 specific gravity gas). Refer to Table C-4, National
Fire Protection Association NFPA 54
†This length includes an ordinary number of fittings.
7. After completing unit conversion, perform all safety checks
and power up unit.
NOTE: The design and installation of the duct system must be in
accordance with the standards of the NFPA for installation of
nonresidence-type air conditioning and ventilating systems, NFPA
90A or residence-type, NFPA 90B; and/or local codes and
residence-type, NFPA 90B; and/or local codes and ordinances.
ADHERE TO THE FOLLOWING CRITERIA WHEN SELECT-
ING, SIZING, AND INSTALLING THE DUCT SYSTEM:
1. Units are shipped for side shot installation.
2. Select and size ductwork, supply-air registers, and return-air
grilles according to American Society of Heating, Refrigera-
tion and Air Conditioning Engineers (ASHRAE) recommen-
dations.
3. Use flexible transition between rigid ductwork and unit to
prevent transmission of vibration. The transition may be
screwed or bolted to duct flanges. Use suitable gaskets to
ensure weather tight and airtight seal.
4. All units must have field-supplied filters or accessory filter
rack installed in the return-air side of the unit. Recommended
sizes for filters are shown in Tables 2 and 3.
5. Size all ductwork for maximum required airflow (either
heating or cooling) for unit being installed. Avoid abrupt duct
size increases or decreases or performance may be affected.
6. Adequately insulate and weatherproof all ductwork located
outdoors. Insulate ducts passing through unconditioned space,
and use vapor barrier in accordance with latest issue of Sheet
Metal and Air Conditioning Contractors National Association
(SMACNA) and Air Conditioning Contractors of America
(ACCA) minimum installation standards for heating and air
conditioning systems. Secure all ducts to building structure.
7. Flash, weatherproof, and vibration-isolate all openings in
building structure in accordance with local codes and good
building practices.
Table 4—Maximum Gas Flow Capacity*
INTERNAL DIAMETER (IN.)
10
.622
175
.824
360
1.049
680
1.380
1400
1.610
2100
LENGTH OF PIPE, FT†
20
30
40
50
60
120
97
82
73
66
250
200
170
151
138
465
375
320
285
260
950
770
600
580
530
1460
1180
990
900
810
SUPPLY
DUCT
OPENING
Fig. 13—Supply and Return Duct Opening
VERTICAL DUCT COVERS
Fig. 14—Vertical Duct Cover Removed
10
70
80
90
100
125
150
61
57
53
50
44
40
125
118
110
103
93
84
240
220
205
195
175
160
490
460
430
400
360
325
750
690
650
620
550
500
RETURN
DUCT
OPENING
175
200
—
—
77
72
145
135
300
280
460
430
C99089
C99012
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