Abstract: A flue exhaust fan has a configurable upwardly facing outlet for delivery of a mixture of gas and ambient air from the water heater or a furnace into either a vertical flue or a horizontal flue. Because the horizontal flue necessarily includes a 90° transition between the upwardly facing outlet and the horizontal flue, the horizontal flue has a greater flow resistance than the vertical flue. By installing a straight connector with a flow resistance element, the gas flow resistance encountered by the flue exhaust fan is the same for a vertical flue and a horizontal flue therefore requiring a single flue exhaust fan with a flow rating for installation with a horizontal flue or a vertical flue.