OK, I've now read the book and reread it. Instant downloads and PayPal, gotta love it.
A fireplace conversion is not specifically detailed: Ianto and Leslie walk you through a "vanilla" proven-to-work stove design and implementation, all the while discussing all the principles that make or break a particular design. I like this. When you have these concepts downloaded into your head, you start looking at your fireplace, breakfast nook, corners of rooms, etc. and mentally working out the relative benefits and challenges of arranging mass heating for each application.
Some of my initial thoughts follow, but the concepts are still mixing and combining and combusting in there...
-> Possible to do the rocket part all in brick, mortared together but just laying on the flat floor of the fire place so it can just be hauled out and broken up at moveout. Work out how you want to make the ducts happen for a) hot air from the stove/fireplace into your heated furniture and b) cooled air + H2O + CO2 etc. back into the fireplace, reheated for flow up the chimney.
-> Surround the heat riser stack-o-bricks with cob to insulate and form a horseshoe shaped space for the air. Split the horseshoe at the very back to separate the new hot air emerging from the cooled air that gets pushed up the flue / chimney.
-> 2 foot 4 inches sounds like Just Enough vertical space for a heat riser. If you can get it hot enough. At the top you still have to "U-turn" the hottest air, could be a plate shaped to block the top fireplace opening but with a hole for an exit/exhaust flue on one side. You don't get to use the heat at the top like you do with the basic "barrel" model though. Unless you count heating the (house's) chimney, which is a Good Thing to reduce condensation and creosote and consequences of corrosion and crud...
-> Alternatively you could do a heat exchange barrel half-in, half-out of the fireplace. Sideways burn tunnel. You get the hot lid for teapot, radiant heat from the barrel. This also brings the design back toward the model used in the book. Aesthetically this could take you away from or closer to the look you want to have.
On mine (kind of an arc fireplace in a corner), I'm leaning toward all brick rocket in the fireplace, 8" flue system, and the heat storage built in two parts: hearth extension in front of existing hearth, then to the side as a 9 foot bench w/two lengths of duct to round-trip back to the fireplace for exhaust behind the stove-assembly and up the chimney.
Massless heater could have a metal (opened barrel section?) piece across the whole fireplace opening that gets hot and has just the feed tube emerging in front of it...
Good one!
