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This does not apply if the 90° elbows are used to increase or redirect a vertical rise. Figure 12 Example: According to the vent graph (Page 15) the maximum horizontal vent length in a system with a 7Z\x’ (2.3 m) rise is 20’ (6 m) and if a 90° elbow is required in the horizontal vent it must be reduced to 17’ (5.2 m). In Figure 15, dimension A plus B must not be greater than 17’ (5.2 m) • The maximum number of 45° elbows permitted per installation is six (6). These elbows can be installed in eit