Anyone have a rocket mass heater in their greenhouse?

Is anyone out there in permie-land have a working rocket mass heater in a greenhouse? I live in Canada, spring time, we can get temperatures down to minus 10 and occasionally colder.. That makes seed starting in the hoop house testy to say the least.
We are wondering about the possibility of a rocket stove with the heat sinq being the soil in the bed instead of the cob mass. The seedling trays would be put on top of the soil, not in the soil.
Also there is the question of the barrel inside or should we build a small addition on the end to house it? The hoop house is 24" long 18 feet wide with double walled production greenhouse plastic.
Thanks
Evonne

Evonne Smulders

I think a few folks have them.

I'm building one into my new greenhouse.

This video shows how how I did the venting under the floor for a thermal mass: vid 1
This one is how I build the heater: vid 2
and this one is how I modified it shortly after! vid 3

-Rob T