Thank God for this forum! I was about to build my pit all wrong! I should be getting my plasma cutter within the next two weeks. So I am close to starting my build. I ran through the calculators that I found here and this is what I can up with it. 20" Dia pipe x 36" long = 11304 in^2 Firebox 16"x16"x18" = 4608 in^3 ~ 122% 4" chimney pipe 18.5" long FB to CC opening 4" segment w/ 1" dam RF plate 6" segment = 79.267 in^2 RF plate 18 1/3" w x 31.5 long leaving 4.5" gap at end =82.485 in^2 RF plate 1/4" slope My questions: 1. Is a 1/4" slope good enough for the RF plate to drain? 2. When I cut out my single large door I was planning on leaving 2.5" each side making it a 31" door. Is that good? 3. how big of a dam should I have at the end of the RF plate? Is 2" good? I got most of the stuff I need for the build except the smoke stack. I need go to a scrap yard b/c brand new cost too much.