Bosch HMV9302 Installation Instructions - Page 9

STEP 2: PREPARE THE VENTING SYSYTEM STANDARD FITTINGS NOTE: If the existing duct is round, you must use a rectangular-to-round adapter, with a rectangular 3" extension duct installed between the damper assembly and the adapter to prevent the exhaust damper's sticking. DUCT LENGTH The total length of the duct system, including straight duct, elbows, transitions, wall or roof caps must not exceed the equivalent of 140 feet. For best performance, do not use more than three 90 degree elbows. Below are the standard fittings and their equivalent length in feet. 1 2 3 3 1/4"x10" to 6"=5ft. 4 5 3 1/4"x10" roof cap=24ft. 6 3 1/4"x10" 90˚ elbow=25ft. 7 90o elbow =10ft. 3 1/4"x10" wall cap =40ft. 45o elbow =5ft. Figure 9 3 1/4"x10" flat elbow =10ft. To calculate the equivalent length of each ductpiece used, see the examples below. For 3 1/4"x10" SYSTEMS Examples 3 1/4"x10" 6ft. wall cap 90o elbow 2ft. For 6" ROUND SYSTEMS 90o elbows 6ft. wall cap transition 2ft. 1-3 1/4" x 10" 90o elbow 1-Wall Cap 8 feet straight duct TOTAL LENGTH = 25 ft. = 40 ft. = 8 ft. = 73 ft. 9 1-transition 2-90o elbows 1-Wall Cap 8 feet straight TOTAL LENGTH = 5 ft. = 20 ft. = 40 ft. = 8 ft. = 73 ft.