A couple of years ago I built a new, larger than it needed to be (2800 sq.ft.) house. I've heated with wood for years and had often looked at the possibility of having a masonry heater built. Now was my opportunity. So, in the new construction I included a masonry heater. The attached image is NOT my heater, but is very similar.
I am very disappointed in its performance. This is no reflection on the mason -- he did a good job and I think the heater is built to all modern standards of mass masonry heaters. However, it takes a huge amount of fire to heat all that mass, and in the process the thing smokes continually (outside), smells of creosote, and is a concern for me developing all that junk in the flue. I actually don't like to burn it.
My heater has an additional door above the main fire box, -- an "oven" with an iron/glass door. Soot accumulates on the door leaving the glass black. It takes about six hours of a large continuous fire to get the oven hot enough to burn off the soot -- for the oven to "go white," and that is with the fire blasting straight through a slot in the floor of the oven from the firebox. It's essentially a RMH without the "rocket" riser tube. This lack of complete combustion seems to be a real problem in my current mass heater. The highest temperature I've ever been able to get on the cleanout doors there at the bottom of the heater is 160F -- a great place for creosote and soot formation.
I was wondering about installing a batch box rocket burner in the existing heater -- essentially just installing the riser tube (with some other minor mods to get the fire properly into the tube). Can it be safely done. I think there is enough room to get it in there. May have to knock out the pizza oven floor to get enough height for the riser tube. There would be at least 36 inches available from the bottom of the existing firebox to the top of the oven. I know it will still take time and fire to heat all the mass, but I'd like to improve the burn characteristics of the heater.
I was thinking about the straight in P-tube design with secondary air.
Before I start ripping anything, I'm also thinking I'm going to try introducing secondary air into the top of the flame path just before it enters the upper oven area. I can easily install that and see how it does.