Unfortunately, I didnt get my two heating solutions finished before cold set in. With work, family, and short days, Ive not had the time Id hoped to finish things off.
Another concern Ive had is getting things too warm. Since my greenhouse is so tiny, I had visions of scalding water and melted plastic. So I wanted to measure temperatures with the rocket mass heater without it being connected to the greenhouse.
This past week I finally got the rust stripped off and painted the drum and lid (from a second-hand 22.5" Weber grill) with high temperature paint. The high temperature paint is supposed to be able to go to 800 degrees Fahrenheit without out-gassing or burning off.
Ive got a video here showing how I assembled the innards. I want to be able to disassemble the rocket mass heater, so making the components of cob isnt my first choice. If I had a chance to do this over, I would cut two 8 inch holes into the base plate or "lid" of the barrel.
Ive found that its a bit tricky getting these heaters to start. The method that ended up working for me is to start off with crumpled newspaper and a wax & eggcarton fire starter. Then feeding in small diameter sticks with the occasional piece of junk mail works great.
In my initial burn, I found that the top of the barrel (inside the domed lid) got to about 400 degrees Fahrenheit. The sides of the barrel warmed my hands when held about an inch away, and the top of the domed lid provided a similar level of diffuse heat.
If I had a greenhouse that was taller and could make a second version of this, I would consider having the heater inside the greenhouse. My greenhouse is short, however, so the roof plastic would only be a few inches above the domed lid. And this first version has the big rough rectangular hole for the exhaust, so I would be concerned about the exhaust fumes leaking in the enclosed space.
My next step will be constructing a nicer base out of bricks and connecting the exhaust to the duct work and structure inside my greenhouse.
