do you mean for the riser tube or the body of the stove?
I know you can get smaller diameter culvert but I think it is galvanized and I know that heating galvanized steel will give off zink gas and that is not good to be breathing.
I would pass on using the culvert for any of the combustion area. The zinc galv coating makes it moisture resistant. It would certainly get hot enough to burn off the zinc - but thats a mess, and the zinc fumes can make you sick. Also the gauge on them is going to be too small to really last. At RMH temps steel oxidizes and flakes away pretty fast
What's brown and sticky? ... a stick. Or a tiny ad.
GAMCOD 2025: 200 square feet; Zero degrees F or colder; calories cheap and easy