Just wanted to share a project I built 6 years ago to heat my kids swimming pool. It's all stainless steel, has been running every summer now since I built it without a issue. It will heat the ~10000 gallon above ground pool from ~60f to 90f in about 3 hours. I had issues with it smoking when I tried to run it natural draft, But since I have added a High temp power vent, its completely smokeless except for a few minutes during startup. Once running for a hour or so, the stack temp is around ~350-400. Cheers!