Flexible Ducting for Rocket Mass Heater

Hello!

I'm wondering if it is possible to use flexible pipe to induce additional turbulence to extract more heat from a vertical section of exhaust because I'm having trouble fitting a long run of horizontal pipe in my available space.

I'm currently planning a RMH as a bench/daybed in a 16 ft diameter round room. The total area to be heated is about 800 square feet, with roughly 500 sqft on the main level and an additional 300 sqft in a loft area above the heater. The walls are earthbag, so the building already has a lot of mass that I would like to utilize for the heater.

I'm planning to build an 8 inch J-tube and the distance between where I want the feed tube and where I would like the chimney to exit is about 16 ft (measuring along the curve of the wall). Due to the curvature of the wall, I'm having trouble fitting multiple runs of exhaust ducting in the space I have to build the bench while maintaining accessibility for cleaning.

My idea was to run about 12-15 ft of rigid ducting in the bench and then use flexible ducting with some twists and turns for the vertical component after my pipe leaves the bench and starts heading to the roof to dispate the remaining heat into the wall. I have about 8 ft of wall height before I reach the ceiling and the ducting could be cobbed/plastered right onto the wall.

Would I be able to extract enough heat from the exhaust using this set up? Could I use corrugated flexible pipe to slow the air movement in the vertical section or would it create to much drag in the system? I read that 1 ft of corrugated equals about 10 ft of smooth wall in a horizontal run, but would that calculation be different in a vertical run with more updraft? If corrugated piping is unwise, could I use a "smooth wall" steel flue liner instead? Would zig-zagging rigid pipe up the wall be more effective?

Thanks for any tips or advice, and I am open to other suggestions on using the walls as heat storage.

Hi Cal and welcome to the permies forums!

Round rooms are always more difficult to build using straight exhaust pipes.
The heat extraction area of rmh's is often not built with the thought of inducting extra friction to slow the gasses down but rather to allow the gasses to naturally stratify through the use of bells.
This is often a much more efficient way to capture a lot of the heat before it exits the chimney without sacrificing draft.
Bells are also not restricted to shape and size. If you don't have the floor space, you make them tall. If you have a creative design, they can be made curvy and spread out through several branches.
Lots of possibilites to consider.

wood-heat-storage-flues-vs-bells

Hi Cal;  
Welcome to the wonderful world Rocket science!

Gerry beat me to it.    You would like a bell system much better than a piped mass.
Check them out and I think you will agree!

Thanks for pointing me in the right direction!

After reading up on it a little, a bell design seems like a good fit for my space and a better way to utilize the mass I already have in the building.