I have an Englander PDVC pellet stove that came with my house when I bought it in the spring. Never used it. Currently its vented through the wall and comes straight through the exterior of the house a couple feet. The existing is getting rust but also leaves some soot on the exterior of the house/ What I want to do is go out about the same length but put an elbow to go up at a 90 about 3-4 feet and put some type of cap that will prevent rain from coming through it. I am pretty handy but never really worked with HVAC duct work before. What do I need to do this?