Carrier 59TN6A Installation, Start-Up, Operating And Service And Maintenance Instructions page 49

NOTE: Maximum Equivalent Vent Length (MEVL) includes standard and concentric vent termination and does NOT include elbows.
Use Table 14 - Deductions from Maximum Equivalent Vent Length to determine allowable vent length for each application.
Altitude
FT (M) 5
Unit Size
40,000
50,000
4501 to 5000
(1370 to 80,000
1524) 100,000
120,000
40,000
50,000
5001 to 8000 80,000
(1524 to 100,000
1829)
120,000
40,000
50,000
8001 to 7000 80,000
(1829 to 100,000
2134)
120,000
40,000
50,000
7001 to 8000 80,000
(2134 to 100,000
2438)
120,000
40,000
50,000
8001 to 9000 80,000
(2438 to 100,000
2743)
120,000
40,000
9001 to 50,000
10,000 80,000
(2743 to 100,000
3048) 120,000
Table 15 - Maximum Equivalent Vent Length - Ft. (M)
4501 to 10,000 Ft. (1371 to 3048 M) Altitude
DIRECT VENT (2-PIPE) AND SINGLE-PIPE
Vent Pipe Diameter (in.) 1
1-1/2 2 2-1/2 3
NOTES:
1. Use only the vent pipe sizes shown for each furnace. It is NOT necessary to choose the smallest diameter pipe possible for venting.
2. NA - Not allowed. Pressure switch will not close, or flame disturbance may result.
3. Total equivalent vent lengths under 10' for 40,000 BTUH furnaces from 0 to 2000 ft. (0 to 610 M) above sea level require use of an outlet choke plate.
Failure to use an outlet choke when required may result in flame disturbance or flame sense lockout.
4. Not all furnace families include 140,000 BTUH input models.
5. Vent sizing for Canadian installations over 4500 It (1370 M) above sea level are subject to acceptance by local authorities having jurisdiction.
6. Size both the combustion air and vent pipe independently, then use the larger size for both pipes.
7. Assume the two 45 ° elbows equal one 90 ° elbow. Wide radius elbows are desirable and may be required in some cases.
8. Elbow and pipe sections within the furnace casing and at the vent termination should not be included in vent length or elbow count.
9. The minimum pipe length is 5 ft. (1.5 M) linear feet (meters) for all applications.
10. Use 3-in. (76 mm) diameter vent termination kit for installations requiring 4-in. (102 mm) diameter pipe.
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