My damper is stuck open and I've got no chimney cap. I'm concerned about rain, birds, critters, snakes, etc...getting in my house through my chimney flue & vents. The flue is 13inchx13inch and the other 2 vents are basically a concrete block on it's side being used to vent a convection oven + built-in grill (does not work; planning to demo) in the kitchen. I'm not finding many with experience on chimneys/fireplaces in this area but one co. I called told me that I could not put a cap on it because the flue and vent openings are flush with the chimney top. Also the chimney top is flat but should be pitched away from openings. I was told that if I want to put a cap, I have to chip away some of the concrete around the flue & vent openings and add enough additional flue/vent to rise above the chimney top to be able to attach a cap...then I need to build up and pitch the chimney top away from the new higher flue/vents. Thanks, your thoughts and opinions are greatly appreciated.