Sherry N Johnson

I have been researching to build a RMH, 8" version. I'm now seeing the batch box and frankly the higher heat of the batch box at the heat riser barrel kind of scares me. While I really like The idea of the fire bring enclosed behind a sealed door, and the more efficient burn, the temps are crazy. The ceiling would only be above 36 to 40 inches above the barrel top for a RMH and about 23 inches above a bathbox double barrel. I fear the ceiling would dry, become brittle and catch on fire.
I'm in central Indiana where the temps remain in 20° to 30° range from late November to early March with a week or two of temps down to -20°. I live in a walk out basement. Half of my living quarters are below ground. I am completely surrounded by tall timber.
An a-frame house with loft sits above me, (partitioned off and rented out).
The house is pretty much and open floor plan. The portion mainly underground is 616sq ft, the add on is 416 sq ft for a total of 1032 sq ft. The addition has R19 insulation in walls, R30 in the ceiling. It has a new insulated metal roof. Windows are double pane low e, so are the doors. Foundation is a concrete slab.
The walls and ceiling are 3/8 headed panel pine. The roof slope is 2" in 12".
I plan on the exhaust pipe/chimney being 12ft from the a-frame roof which has a slope of 16" in 12". Would 5ft above the roof be sufficient? 2ft to clear roof slope plus 3 ft. It would be impractical to make a chimney that extends 3 feet above the a-frame roof line. (28 feet a-frame roof plus 2 feet for slope of addition plus 3 feet clearance above a-frame ridge would be a 33ft chimney! Quite expensive as well with triple wall stainless pipe being $145 for 3 feet.