[. . . ] Microwave Hood Combination PRODUCT MODEL NUMBERS GH6208XR GH7208XR Electrical: A 120-volt, 60 Hz, AC-only, 15 or 20 amp fused electrical supply located in the upper cabinet as close as possible to the microwave oven hood. [. . . ] The total length of the vent system including straight vent, elbow, transitions, wall or roof caps must not exceed the equivalent of 140 feet of 3-1/4" x 10" rectangular or 6" diameter round vent. To calculate the length of system you need, add the equivalent feet for each vent piece used in the system. 3-1/4" x 10" vent system 3-1/4" x 10" 90° elbow 6 ft. wall cap Recommended standard fittings 3-1/4" x 10" to 6" = 5 ft. 3-1/4" x 10" roof cap = 24 ft. 3-1/4" x 10" 90° elbow = 25 ft. 90° x 6" elbow = 10 ft. 3-1/4" x 10" wall cap = 40 ft. 45° x 6" elbow = 5 ft. 3-1/4" x 10" 90°flat elbow = 10 ft. For wall or roof venting methods: If the wall exhaust method is chosen, be sure that there is proper clearance within the wall for the damper to open fully. that length of vent and number of elbows should be kept to a minimum to provide efficient performance. using caulking compound to seal exterior wall or roof opening around cap. NOTE: If flexible metal vent must be used, calculate each foot of flexible metal vent as two feet of rigid metal vent. Flexible metal elbows count twice as much as standard elbows. 2 ft. 1 - 3-1/4" x 10" 90° elbow 1 - wall cap 8 feet straight Length of 3-1/4" x 10" system = 25 ft. [. . . ] For complete details, see Installation Instructions packed with product. [. . . ]