Hi, i am in the plumbing and heating trade for 30 years master plumber/oil burner/ propane n.g tech. I currently heat my home, 2400 sqft plus full basement in western Maine with a 11000 btu oil boiler and more importantly a old Shenandoah wood furnace. The wood furnace was recovered from a boiler swap out i did 20 years ago, it originaly had a hot water coil inside the fire box but had long since expired. I set this unit up in the center of my basement and it is connected to a 45' tall interior chimney. I have since found an old cast iron water jacket that came from a similar stove and have it installed in the fire box. Along with this is 100' of 1/2" soft copper tubing coiled around inside of the duct plenum directly above the stove but not in the fire box. All of this piping is tied together, routed through the cast iron jacket and tied to my oil boiler. I have all the proper safety equiptment installed, and it is set up to run like this.
I start a fire, a thermal switch located just above the copper coils turns on power to a standard heat system pump when the temp reaches 200 this pump simply circulates water from the wood stove to the boiler, at this point the water in the stove portion is only heated slightly. As the fire heats the water that is now constantly moving, a aqustat senses the temp rise. When the temp reaches 180 the aquastat turns on the pump on my boiler that heats the main floor of the house, as the water cools from circulation the aquastat turns the pump off, and waits for the next rise in temp. This system has worked well for me for years, the only drawback is power failer normaly means no more fire untill the power comes back on. My main problem with this system is now in my older age firewood is getting heavy and i burn about 5 cord of wood.
I am interested in the opinions of those of you who use a rocket mass heater for any purpose, im not really interested in a heated bench since it will be in the basement, i am interested in using water as my thermal mass, but i want to be able to obtain 180 + degrees water. I have thought about simply coiling copper tubing through the cob mass maybe wrapped around the exhaust piping, or imbedding a small tank within the mass. There is also the barrel where a coil could just sit on top or be wrapped around it(i have seen this crudly made) in the end i fear after all the work i may end up right where i am now or slightly worse off, if i cant reach the temps needed.
Here is my question.....if you heat with a rocket mass heater how would you attempt to heat water to these temps if you where not concerned with safety? (sorry but i will take care of the safety aspect)