Back when I was building my outdoor wood boiler or stove.. I looked at all of the brands out there ( many more now ) I was lucky enough to do business with Wood Dr., Central Boiler, Heat-Mor and others. There was another inWisconsin selling Boiler Plate units stating that they were similar to what ships used to use. From what they told me, It was more ductile than regular carbon steel when used in a pressure situation. I looked around there were so many grades with so many ratings I just said the heck with it and used 7/16" mild steel. I used 7/16 because a friend with a roller had some to get rid of. Many of the stove companies use 1/8" MS or 304 or 409 SS. I'm not sure why you would need SS or Boiler Plate because most stoves are completely surrounded with water and rarely get hot enough to boil the water. That's why yhey last so long and mine has no pressure buildup at all. Use anti corrosion in the water and try to keep the stove as hot as possible to battle creosote. I looked at all above mentioned modles and a few more, Then built my own. Cost about $1400.00 but I have not burned a drop of Propane in 4 years,. You can set it up for pottable hot water too. If you have any other questions I would be glad to help. I learned a lot about the whole system including in floor heat and all that is needed.