Hello Well I wonder if anyone else has a vent pipe coming out of the roof that is too short? You may and not know it? From http://www.doityourself.com/forum/plumbing-piping/351561-vent-pipe-roof-whats-min-height.html#b "According to my code book from IPC, unless some changes have been made, The lowest acceptable height of a stack in NH is 12". We have snow here so where you live may be different. And must be 2' above and 10' away from any opening window." However I have also seen 6" as a min and recommended height of 18" ! ! ! Well I have the 12" height from the roof here in Salem NH done in 1962. I am sure that is not correct. There is alot of warm air from the shower and other fixtures in the full bath that comes out of the stack and condenses to melt the snow and cause re-freezing and such on the roof. I also believe that this has caused the rubber boot to become so brittle it broke and now there is a Huge space where water can get in! ! ! So we cut the old boot away and put a new boot and used a whole tube of black roof sealant! Using 3" PVC and a clamp, extended the pipe to 25 Inches! Above all codes and more important above all snow! I used some black grill paint to make the copper, PVC, stainless steel clamps and the aluminum boot base all the same color! See pics click to enlarge!