Kevin is on the right track here. I've installed 6-700 freestanding wood stoves in the last 12 years, it's my winter job. U.L. listed stoves should have clearances on the back of the stove to combustibles. If you can't make these clearances in a practical manner, wonder board/concrete type of wall board with a 1 inch space between the wall and the board will narrow this down to a few inches. A cheap way is to cut rain gutter nail supports for the spacers. Also while you're back there, many stoves that exit out the back have removeable boots that can be turned upside down to exit straight up Out the wall IS NOT a good idea, draft problems may occur. A minimumn of 12 feet of pipe from top of the stove to the cap is recommended. For every 90 you add, 3 feet of pipe may be needed for a good draft. Here's how I do installations. Spot the stove where you would like, getting your proper clearances. The support box for the class A pipe (the pipe going through the roof) can be installed between the rafter, as close to directly above the stove as possible. 2 2x4s can be positioned to hold the box, nailed between the rafters. Drill 4 holes in the support box, leaving at least 2-3 inches of the support box below the rafters. Mount the box, using a torpedo level to insure it's level, with screws to the 2x4s. We use hex head screws and a cordless drill for this. If the box isn't level, your pipe coming out of the roof won't be level either. Now, using a plumb line, drill a hole through your roof, dead center of the hole through your support box. Take your flashing to the roof, spot the drilled hole in the center of the flashing, scribe the hole from the inside of the flashing, cut a square hole with a skill saw. Pop the cut material, throw it away. Now take a putty knife and a screw driver, try to slide the flashing under the shingles to where half the top of the flashing is covered by the shingles. Use the putty knife or screwdriver to pull any nails or staples so the flashing will slide under the shingles. Now you're ready for the class A pipe. You should have what is called a P connector, it will attach to the class a pipe that goes into your support box, a inch or 2 will stick out of the support box, this is what you attach the single wall pipe to. Your class A pipe should be a minimumn of 2 feet above your roof within a 10 foot radius. In other words, if you had a 10 foot long stick that you held level 2 feet down from the top of your class a pipe, it wouldn't touch any part of your roof. Clear as mud? Most codes call for a minimumn of 2 feet out the roof, also. Attach enough of the class a pipe together to get you out of the roof, drop it through your flashing into your support box. Add more if needed. A storm collar pushed down tight to the flashing, use some high heat silicone to seal. Put your cap on, you're done with the top. Down to the stove. You have 8 inch pipe, you can use an adapter on the stove to downsize to 6 inch, class A and inside pipe, it is cheaper and probably will draft better. If possible, straight up from the stove, 45 elbows at the support box if needed, better clearances and draft. If you have to elbow at the stove top, same thing if you need elbows to attach to the class a. Slip pipes are available, one slips inside the other, telescoping. Measure the distance from the top of the stove to the p connector, this will give you an idea on total length, what size slip to use. Use self tapping stove screws to attach the pipe together. Any questions, give me a pm. Going out through the back wall is usually about 2-3 times more expensive than straight up, more class a pipe, more expensive support box, strapping to keep the pipe away from the wall. Class a pipe has clearances also, 2 inches on most I know of, if you run into a roof truss problem, cut the truss and add a cripple for support. We charge $350 for one of these jobs, takes us 1-2 hours, tops. I would expect total cost of materials, top to bottom, about $500. Kev is right on about pipe fit, it should fit inside as it comes down, prevents creosote drip. Good luck, Dan