posted 9 years ago
OK, I suspected that this was a basement build, which are very difficult in most cases to achieve satisfactory performance from an RMH. In any "normal" installation having a good naturally drafting chimney system is an important criterion. Once the chimney problem is addressed, then I'd heed the advise the guys have presented before proceeding with the build.
A few notes, adding to that already mentioned by the guy's posts above.
Since the feed (opening) measures 6 x 7 inches, the burn tunnel should be the same. 6 W x 4.5 H burn tunnel will be susceptible to clogging with ash and coals. Better to have the burn tunnel taller than it is wide if it must be unsymmetrical. Since this is a 6" system (bench ducting size) I'd go 5.5 x 5.5 to 6 x 6 inches throughout the feed and burn tunnel. Doesn't have to be exact, and even 5 x 6 inches (width x height) will work.
When an RMH is working correctly and come up to full operating temperature, any paint left on the outsides / top of the barrel will burn and out-gas toxic fumes. So do clean the barrel of paint, at least the exterior, if that hasn't already been done.
Al is correct about the bench being to long for 6 inch ducting. The size of your layout is more along the lines for an 8" system (8 inch J-tube rocket with 8 inch bench ducting). Otherwise, if you intend on staying with 6" bench ducting, I'd shorten the bench run by removing the two long parallel pipe sections that connect to the 180 hairpin turnaround. HTH.