Hi folks, I'm getting ready to install an OAK on my Harman Accentra insert. I don't want to run it up the 25' flue, so I was planning to core a 3" or 4" hole through the back of my fireplace, which has an outside chimney. I have a couple questions I thought the folks who have OAKs installed this way could help with. 1. What size hole to core? I assume a 3.25" hole would be perfect for a 3" pipe, but is a 4" hole with silicone caulking around the pipe OK? 2. What do you use for piping from the frame stub to the outside? Pros and cons of flexible vs. rigid? 3. Is condensation an issue? If so, what can be done to minimize any negative effects? I have a lot of left-over Roxul insulation from the block-off plate install if that can help somehow. 4. Should the pipe be sloped or level? If sloped, up or down going from the stove to outside and the reason for direction of the slope? 5. What do you use for a inlet cover on brick and mortar chimney? I would prefer to avoid buying the $60 Harman part if a galvanized dryer hood with some 1/4 inch screen and the flap removed would suffice. 6. If I should ever want to remove the stove and restore the fireplace functionality, can refractive mortar be used to close the hole? I'm thinking that I could tightly stuff the hole with Roxul leaving 4 inches to fill with mortar on each end. I appreciate your comments and suggestions. Thanks!