Anyone have any suggestions or experience with the OAK (outside air kit) for a Mt. Vernon AE insert? Because of the way my fireplace was built, the only option I have is to run the OAK and flue out the top of my masonry flue. The flue is located in the center of the house.I currently have a combination 3 inch flex with 3 inch double wall pipe vent that is 18ft long. I'm thinking that while I am installing the OAK I might as well change out the vent to a 4 inch system. Should I fabricate the chimney top termination for both pipes (suggestions/ideas appreciated) or could you suggest a good (reasonable) place online to get one? Did you use the factory OAK or fabricate your own? Did you use aluminum flex or some other type piping? What size? I also need suggestions on what type (flex or double wall) for the 4 inch and where online would be a good place to purchase the kit? What needs to be done, if anything, with the unsealed uninsulated damper area where the oak and flue will be going thru? Any and all suggestions, photos, diagrams or comments greatly appreciated. Thanks!