with a harman stove the inner pipe liner goes inside the tail piece and the outer pipe goes over the tail piece which seals the 1/4 inch gap and seal with the silicone you apply to the tail piece.with a st croix and others the inner pipe goes over the tail piece and leaves the 1/4 inch gap open. in a perfect world where all the joints are perfectly sealed you will not get smoke from this area. but normally this is not the case. i learned this the hard way. i tried to save you the trouble of going through the whole learning curve. seal that gap and smoke will be gone!