i'm trying to hookup an old jotul woodburner in my garage,there is exsisting double wall chimney, or stove pipe hanging down from ceiling. i have single wall to hook into it but ,don't know if there is an adapter needed to go from to the other. also,on the stove where the pipe hooks in,the actual stove coller is 43/4 outside, and 43/8 inside so trying to come out the back with aa 5'' to 6'' elbow leaves a little slop between the collar on the back of the stove and the 5'' end of the 90. any safe suggestions? thank you