Thank you for your question on the model EH6 exterior inlet/outlet hood for our indoor air quality units. This model includes a bird screen but does not include a back draft damper. The Broan model 641 wall cap is for a 6" round duct and would include a built-in backdraft damper and bird screen. This is offered in an aluminum natural finish and is for use with our ventilation fans. If you have further questions, please contact our Technical Support department directly at 800-637-1453.