What type of exhaust duct should I use for installation?

You should use a 4-inch (10.2 cm) diameter rigid aluminum or rigid galvanized steel duct. If a flexible metal duct must be used, use only the type with a stiff sheet metal wall — never use plastic, thin foil, or non-metal flexible duct as these present a fire hazard. Joints should be secured with duct tape, not screws. (Page A-2)