An Idea for an outdoor cob fireplace to provide indoor heat

[Lucy Guss]

I've been eyeballing my location for a possible RMH in my house, and I am more and more thinking it isn't that doable space wise. So I've gone back to the drawing board. Here is what I was thinking.

How about a cob oven (with no insulation around it) then building another cob space above it to capture the heat. Then insulate the exterior of the whole thing. Run a pipe into and out of the upper air space of the cob oven, with the pipe going into the house on both ends through a window or whatever else, and forcing air through the pipe via a small fan?

Obviously, this lacks the efficiency of an RMH or rocket stove, but it may allow for a slightly lower temperature and longer trapping of heat than would something like a couple of barrels doing something like that or a standard outdoor forced air furnace.

[matt walker]

Well Lucy, it's an interesting idea for sure. My gut feeling is you would use a whole lot of wood, and when you needed heat the most would be when you really didn't want to go out there and feed it, among other concerns. That said, my neighbor heats his tiny house with a small RMH, and he did install some ducting through the mass which he drives air through with a small computer fan. He feels like it is a great way to move heat from the mass to where he needs it.

I believe I remember that your location is quite the challenge for an rmh installation. Is it possible there is another spot in the house you could build that you haven't thought of?

[Oddmar]

I Don't know if you have somewhere you could install a 'normal' wood fireplace in your house, but i have a RMH design that takes up about the same space.



Exhaust plenum (purple) feeds into a large Concrete "bell" on the right, which has an ash cleanout in the bottom front. Duct feeds under the RMH firebox to the other concrete "bell", which has a short dividing wall in the bottom just a little higher than the output pipe, causing the remaining hot gas to fill the top of the bell before exiting. There is another (probably unnecessary) ash cleanout in the bottom of the second bell. The tee in the output pipe is to help get a draft flowing when lighting the stove.

I'm planning on building one like this in my friend's shop. I'll make the feed chamber front out of thermo-ceramic glass, and build the unit to look like a conventional fireplace.

[Lucy Guss]

My apologies for not responding sooner. I have been meaning to measure the space to respond, but the great Raccoon in the Duckhouse Fiasco of 2013 has kept me hopping on the farm. So for now, I shall estimate.

You are correct in your memory. My house is an old farmhouse on a post-beam foundation and no basement, so an RMH in most of the house is not suitable. There is a laundry room addition that appears to have been at one time a patio or porch that was later enclosed. Whatever it was, it sits on a concrete slab of some sort. This appears to be the only suitable location in the house for anything of significant weight, be it an RMH or a wood burning stove. There is another addition on the other end of the house on an equally inappropriate foundation as the main house, and there is a fireplace there. The fireplace is some sort of 1970s manufactured fireplace, and the surround appears to be a facade and not actual brick. Removing it completely would provide room for a typical wood stove, but there is not sufficient support for anything terribly heavy.

So . . . The laundry room space is on the outer wall. It is about 20" deep and about 5-6' long. There are windows above it starting at about 3' off the floor. The space seems a little small for an RMH -- primarily due to the depth, though perhaps a mini system with a smaller barrel might work. However, directly below those windows is a nice big space and a nice big slab where I could build something outside and run the heat from it through the window(s) in the laundry room. Any thoughts you guys might have would be great.

I have plenty of ability to get firewood, as I have about 20 acres in timber. We lose more trees every year due to weather than I could possibly burn in a year. That said, it's not so wonderful for the environment or my time. I'm also not looking to this as a primary heat source, but as supplemental and backup. I do plan to build two solar space heaters to supplement too.

[matt walker]

Lucy, post and beam with no basement is actually a pretty good candidate for a RMH in my opinion, depending on the height above grade. Can you get under there and use pier blocks to support a section of the floor? My RMH is on a suspended floor which I reinforced in a similar way, and if you keep it fairly modest you can most likely make it work. One thing to keep in mind is that although they look large, they actually create useable space whereas a fireplace or box stove with no mass creates dead space which you cannot use except for drying boots or something. I have been able to reduce the amount of furniture in my living space by half by creating the heated seating.