Chimney design for greenhouse heater

Hi fellow permies

Am needing a heating system for my greenhouse during the cold months of the winter.

I have access to a load of house bricks for free and i will be building myself a rocket stove.  The idea is for the rocket stove to sit just outside the greenhouse with the exhaust pasing through some brick channels in the floor of the greenhouse (essentially the footpath) and then exiting outside into a chimney.

The rocket stove could also be used as a stove at other times so it would have to have some sort of bypass.  

Just wanted some opinions on the best layout for the brick floor chamber and whether or not this would even work.  Kinda resembles a rocket mass heating bench in my mind.

So do i go for a single chamber, with the chimney at the other end of the greenhouse, or a double chamber so that it returns back to the entrance point, thus giving up more heat out of the exhaust gases, or would this cause  a backdraft because the run is too long. Would i need to seal the bricks on themselves (with clay) to save gassing myself in the greenhouse!?

Or are there other problems with the concept?

Thanks in advance

You would definitely want the entire exhaust run sealed inside the greenhouse, so there's no risk of combustion gasses inside the building. The length of the run is based on the size of the system, meaning the diameter of the combustion path and ducting. Each turn adds resistance and shortens the effective length, but if you use a stratification chamber instead of ducting encased in cob then the rules change some there too.