Thanks everyone. Boy I thought I'd read everything, but you guys have increased my knowledge 10 fold. I won't say too late, but in order to institute all of your suggestions, I would have to start over, especially on the insulation parts. I don't have any insulation around the J tube, only cob. I insulted the redwood floor with 4 inches of perlite stabilized with cement and the wall with standard foam wall insulation. I guess I figured that if you can sit on the bench, the heat given off can't be great enough to start a fire. Taking the J tube apart and replacing the cob with stabilized perlite won't be hard. Replacing the riser with a stabilized perlite tube I can do also. I couldn't find 10" pipe and 8" was impossible to pack uniformly. I can replace the exposed flue pipe with double walled pipe. I don't want to wrap it in glass wool insulation being too ugly. If going straight up is the answer I'll do it, but it's a hole in the roof I didn't want.