GE PNM1871SMSS Installation Instructions - Page 5

Installation Instructions NOTE: If you need to install ducts, note that the total duct length of 31⁄4″ x 10″ rectangular or 6″ diameter round duct should not exceed 140 equivalent feet. Outside ventilation requires a HOOD EXHAUST DUCT. Read the following carefully. NOTE: It is important that venting be installed using the most direct route and with as few elbows as possible. This ensures clear venting of exhaust and helps prevent blockages. Also, make sure dampers swing freely and nothing is blocking the ducts. Exhaust connection: The hood exhaust has been designed to mate with a standard 31⁄4″ x 10″ rectangular duct. If a round duct is required, a rectangular-to-round transition adaptor must be used. Do not use less than a 6″ diameter duct. Maximum duct length: For satisfactory air movement, the total duct length of 31⁄4″ x 10″ rectangular or 6″ diameter round duct should not exceed 140 equivalent feet. Elbows, transitions, wall and roof caps, etc., present additional resistance to airflow and are equivalent to a section of straight duct which is longer than their actual physical size. When calculating the total duct length, add the equivalent lengths of all transitions and adaptors plus the length of all straight duct sections. The chart below shows you how to calculate total equivalent ductwork length using the approximate feet of equivalent length of some typical ducts. DUCT PIECES EQUIVALENT NUMBER EQUIVALENT LENGTH x USED = LENGTH Rectangular-to-Round 5 Ft. x ( ) = Ft. Transition Adaptor* Wall Cap 40 Ft. x ( ) = Ft. 90° Elbow 45° Elbow 90° Elbow 10 Ft. x ( ) = Ft. 5 Ft. x ( ) = Ft. 25 Ft. x ( ) = Ft. 45° Elbow 5 Ft. x ( ) = Ft. Roof Cap 24 Ft. x ( ) = Ft. Straight Duct 6″ Round or 1 Ft. x ( ) = Ft. 31⁄4″ x 10″ Rectangular * IMPORTANT: If a rectangular-to-round transition adaptor is used, the bottom corners of the damper will have to be cut to fit, using the tin snips, in order to allow free movement of the damper. 5 Total Ductwork = Ft. Equivalent lengths of duct pieces are based on actual tests and reflect requirements for good venting performance with any vent hood.