My wife and I are currently in the planning phase of building a 40x40 Earth bermed home on our 30 acre homestead in Ohio. We plan on building a rocket mass stove in the center of the main living area. We are interested in incorporating in-floor radiant heating to reach the far corners of the house including the bedrooms. What I would like to do, and planning on doing is installing copper water lines passing through the thermal mass and then into the radiant heating lines.
My questions are, has this been done and how, or is it a terrible idea? Also, any ideas on how to go about this would be appreciated.
If this is the incorrect forum for such a question I apologize. I have been reading these forums for a long time but this is my first post.
Hope Homestead Farms, LLC
Hi Brian, and welcome to permies. Your question is a good one and the answer is mostly "it depends." In general, an RMH warms the immediate surroundings with radiant heat from the barrel or equivalent surface, and warms a certain amount of mass in the form of a cob bench, masonry bell, etc. It's certainly possibly to design a system that will heat water for hydronic underfloor heating, but in order to do this well for a decent sized house you will need to get that water pretty hot. That means less heat to radiate into the room and penetrate the mass.
Basically, if you substitute your underfloor network for the thermal mass component and probably at least part of the radiative component, I think you will have something workable. But I wouldn't expect a "normal" RMH to do all three. The inherent mass and insulation of your building will be a plus. Have you worked out just how much energy it will take to heat the entire dwelling?
In general I think attempting a radiant heat floor using a rocket mass heater is much more trouble than it is worth. As Phil stated, you would need to substitute the radiant heat floor for your mass. One of the key components of the RMH is that it is really meant to heat people and not spaces. I think radiant heat floors are more a method of maintaining a home's temperature than anything else. There is also the complication of needing a pump system to keep the water flowing, not only through your floor, but also to keep your RMH boiler from becoming a bomb.
Good luck and post pictures of your progress when you start. People would love to see them.