The use of a RMH for water heating is like if you would put a heater loop on your automobile, so that when you got home from a drive, you could hook the engine block up to your water heater. The Primary function of the engine is to move the car, the heat generated is a 'byproduct' of that use. This analogy is such that the RMH is firstly a radiant heating device, and secondarily a convection heating device. Now, when you put your derriere on that heated bench, you have conduction heating. You need to make a decision whether this unit is Primarily used for heating water....then, you MUST consider the need for limiting the heat density, to less than 212F/boiling point (unless the water in the piping is pressurized...and THAT's another ball of wax completely..). You DO NOT want, under ANY circumstances that the water in the stainless steel water jacket, or, boiler piping EVER exceeds boiling point...as then you have a steam boiler...DON'T go there, that can be very dangerous. There have been a few who made a masonry heater (or RMH in your case..) and after the main firing chamber ran the flue so it was surrounded by sand , and in the sand was embedded a copper water coil. The trick here is to either make sure the flow is such that it does not get above 180F, which calls for temperature differential control/s, by pass valving that electro-mechanically controlled, or some such arrangement. One way to do something of the sort is to have a large (1,000gal+) holding tank, that its purpose is to 'hold' and store the heat during firing. In that tank you have a separate exchanger coil submerged, so that in the shop at large, when a thermostat calls for heat, a simple Grundfos circulator pump moves the water thru the slab piping. In this way you segregate the two loops, the perimeter heating loop, and the loop that transfers the heat from the RMH to the holding tank. Either way, or whatever you do, you WILL need to have a source of 120vac handy, or, a dependable solar cycle unit...as you can find 12vdc controls, and circ pumps for such an application. OH, what size is this building, what is the R factor of the walls, how many windows, etc, etc....WHAT is the heating load and loss factor, or have you not figured that out yet..?? THAT is where you should start first. Any reputable HVAC contractor should be able to do a Heat loss survey for you (I used to...30+ years ago do them by hand..., it is much simpler now with computer programs..), Good luck, Cheers, Mik
PS....heated slab.!.., what is your heating degree days, climatic conditions, and are you planning on perimeter insulation and thermal breaks betwixt the perimeter footer and wall and the actual heated slab..?? THIS is very important, when I did do heat loss surveys, for the average 'town home' on an 'on-grade' slab, the perimeter that is exposed to the outside is considered to make up 10 -15% of the heat loss of the entire structure. I hope you have figured that in, more on that later, look at US Concrete specs for info, easily found on the 'net. later, Mik
