dual-fired RMH

New to RMH but having big plans ..... and questions. Is anyone aware of the existence of a "dual-fired" (for lack of a better term) RMH, i.e. with firing and combustion set up at each end but sharing the tubing inside the cob/mass heat storage/ structure ("bench, bed, etc.) and exhaust? I haven't thought this completely through and have not the technical oversight of such an arrangement, so wondering on consensus in the community???
Thanks.

You can't make two combustion cores share the same mass ducting from opposite ends. They would each have to have their own ducting. If you had a huge heating load that needed two full-size RMHs, setting them up in a counterflow arrangement to keep the overall mass temp uniform is workable.

Building codes forbid two heating appliances from sharing a chimney, and even if you ignored code, it would probably cause some sort of draft issues depending on the exact layout and weather conditions.

Thanks for your reply. I was thinking about the dually to increase length potential without reducing heat effect due to the cooling air in the ducts. But from the diagrams and photos you suggested seems like that may not be necessary.

How large is the space you want to heat, how is it built & insulated, and what is your climate? What configuration are you thinking of for mass, including approximate dimensions?

For ordinary houses in cold climates, one 8" system is usually sufficient. This can support up to 50' of duct in the bench, minus 5' for every 90 degree elbow. If the bench is wide enough, you can double back and have the duct return to near the barrel so the bench is heated uniformly on average. 20' of bench is a pretty long stretch for most house layouts.