Vertical Coil Thermal Mass Idea

I would like to build a RMH in my shop but do not have a lot of floor space for the traditional bench of thermal mass. I'm wondering about taking the mass vertical for a smaller footprint. I could put mass around an upright stove pipe, but still seems like the straight shot up would carry away the heat.
So what about using flexible chimney liner to make a coil? The coil could be contained in two stacked drums, maybe with something like dry cement and/or gravel poured in around the coil. Possibly even with solid core of bricks in the center.

Any feedback much appreciated!

I would think that all the drag put on the exhaust gasses by all those turns would stall a system like this. Have you considered a bell? There is no real particular shape they need to be and quite flexible to the place where they are being installed. Here is a great resource to describe them and see if it may work for you:  Bell Theory

Gerry Parent wrote:I would think that all the drag put on the exhaust gasses by all those turns would stall a system like this. Have you considered a bell? There is no real particular shape they need to be and quite flexible to the place where they are being installed. Here is a great resource to describe them and see if it may work for you:  Bell Theory

The more I read, I see there's a minimum temperature that the exhaust gas has to be in order to start the process of rising up the chimney. And even if the drag of the turns didn't stall the process like you mentioned, the cooling effect might.
I had not heard of the bell but am very intrigued with it as a middle ground between RMH and masonry heaters, so thanks! Makes me wonder if I can build a masonry bell around a standard cast iron stove to make it more efficient.

Matt Todd wrote: Makes me wonder if I can build a masonry bell around a standard cast iron stove to make it more efficient.

I would think that a lot of the efficiency is lost up the chimney with such a stove so putting a masonry bell around it would not capture any of this heat but rather just help to store some of the radiant heat instead.

Gerry Parent wrote:

Matt Todd wrote: Makes me wonder if I can build a masonry bell around a standard cast iron stove to make it more efficient.

I would think that a lot of the efficiency is lost up the chimney with such a stove so putting a masonry bell around it would not capture any of this heat but rather just help to store some of the radiant heat instead.

Poorly explained on my part. What I mean is building a bell around a cast iron stove with a stub of stove pipe included inside. So the exhaust would go up, then fall around the sides of the stove before going up and out the final stovepipe exit lower in the bell. I will say, filling up a box with smoke and expecting it to know how to go down, out, and up a hole scares me a bit.

Proper draft is key to the whole operation. For example, a properly functioning rocket mass heater even when there is no fire will often have a natural draft that you can test with a small flame or an incence stick over the feed tube. This test should prove to you that exhaust can travel downwards before exiting again vertically.
The one big difference between a rocket stove being the engine of a rocket mass heater vs a regular wood stove is a much hotter fire and cleaner combustion. There would be a lot of creosote and ash buildup in that bell with the cast iron stove in there which would not be good or safe at all. Kind of like putting a VW beetle engine in a ferrari.
There have been others that have modified a conventional stove to make a batch box heater which I think is about as close as your going to get to implement your idea.
Hope this helps!

Batch Box using fisher stove
Batch Box using Jotul stove