The more research I do, the more I come to the conclusion that building my own boiler is the only way to go. There's just nothing on the market that makes the best use of existing [strike]technology[/strike] knowledge. (I won't say technology because many design elements that make an ideal furnace are old as the hills.) I can imagine that is why you built your own unit. I want to burn sub bit and have the option for wood too and its totally possible to build a unit that does both and does it efficiently, but there is nothing ready-made. As far as I can tell, the Biasi-Eko Coal/Wood is closest thing out there right now. It is one of the few units, boiler, stove or otherwise that incorporates heated sec. air. Cast Iron (not good for wood, or even coal tars but it prevents clinkering, corrosion and overheating) And best of all, needs no electricity to operate - why cut the umbilical to the oilman only to establish a new one to the electricity man?
But one nagging thing keeps coming back to peeve me, and you hit on the head - firebrick. Modern heaters have been married to iron and steel since the Franklin Stove of 1742. Sure firebrick takes a whole new skillset to build with, but its the only way to efficiently burn anything. Why cut wood or haul coal only to blow half the available heat up the stack because your heater is poorly designed? I know thats the motivation for your project and mine. Your design is excellent and I just thought I'd turn you on to these Kuznetsov boilers/heaters/stoves/etc. I found on Hearth.com. Its very similar to your design, it does the same things only simpler. You can see in the pics the clever internal risers around the firebox to preheat sec. air and the sec. air openings. The Russian dude who came up with these units is hardcore: he considers a tall chimney "forced draft" and fans totally unnecessary. The fire regulates its own air supply using its own heat. The most unique thing about his units is the "dry joint" he leaves along the firebox. He claims it allows cooler gasses not directly associated with combustion to escape and be exhausted to stack, allowing only the hot gases from the fire access to the heat exchanger. At first it seems counter productive but he backs up his theory quite well. The temps in the "bell" must be insane! Its the only design I;ve seen that sets up conditions for a truly efficient burn - heated secondary air, a secondary combustion zone separate from the exchanger permitting a long residence time at high temp all trapped by a refractory dome and no electricity needed. With the right grates you could burn wood, coal or any combination without sacrificing performance. I'm not keen to build my own boiler, but I think in the end this one will keep paying me back. Hope you get some good ideas.http://heatkit.com/html/lopezs.htmhttp://stove.ru/index.php?lng=1&rs=109