Any of them will work but the rectangular or square tubing doesn't flow as well as pipe. The tubing is more turbulent so it'll need to be a little larger than the pit calculator recommends.
Last edited by Big T on February 13th, 2018, 11:11 pm, edited 1 time in total.
I don’t think it would matter on the thin wall vs heavy. The idea of a chimney is not for heat retention but for airflow.
Something to think about is longevity. Crome only looks nice when it it is properly maintained and kept clean. A heavy wall pipe will not ding or dent but, admittedly, is not as pretty as Chrome.
I might be wrong but im sure i read somewhere that chimney wall thickness should be thin, the theory, if i remember correctly was the thinner material heated up quicker, that heat in the chimney then creates the draw through the cook chamber. Maybe this is more effective with reverse flow than standard offsets. I use car/truck exhaust pipe on my smokers, generally around 2mm thick, I make my exhausts removable so if they are damaged or eventually rust out can be easily replaced.