pipe questions

so if I have a 4.5 inch thick vented brick back wall how close to it can I put single wall stove pipe? how bout double wall?
can I connect single wall to double wall?
I ask this because I was planning on using all double wall. Then someone told me that I would thusly lose all my heat. So I was thinking about using single wall close to the stove where it is next to the brick wall then finish the flue with double wall up to the chimmney. any thoughts?
How true is it that most of my heat comes from the pipe?
Thanks

not true at all. Well not true at all on a efficient stove. Efficient stoves loose a small percentage of heat up the chimney, therefor its sometimes best to use double wall on the inside to improve draft. Double wall is also easy to clean, you just slip up the telescoping piece and tape your trashbag around it. No dissasembling of stove pipe. If your brick wall is up against a combustable, then its considered a combustable, if you have a 1" air space between the brick and the wall you get a 1/3 reduction per NFPA 211.