Work at a shop that sells stoves and had to do a reinstall of pellet pipe because the old was leaking. Used all new pipe (Pellet Vent Pro) came off the tail pipe to a clean out up to a 90 and out. Siliconed the tail pipe as well as around the pipe going out but still the pipe is smoking. You can see it and I am at a loss as to why other than the thought of negative pressure in the building and how to test for it.