A duct diffuser is different from a room outlet. A duct diffuser is an expansion of duct size where the duct takes in or discharges air to a large space (usually the atmosphere). A stack discharge diffuser with a 14° included angle that doubles the duct area at the discharge reduces the C from 1.00 to 0.33. The performance of a vertical air inlet with a conical cap (C=1.2) can be improved by installing a 1.0D - 1.25D cone diffuser on the inlet end of the duct (C=0.3). Fan discharge diffusers and other connections are discussed elsewhere in this Section.