As with many DIY projects, this project has had its good phases and its troubled phases. One trouble was that the junction between the first barrel and the additional third of a barrel that I put on top of that first barrel let through smoke too easily. I had to do away with that extra height on the first stack using ceramic wool and self tapping metal screws as a lid for the first barrel.
Another issue I found was with the draw. Once the fire got going the draw was okay, but most of the time there was not enough draw and the smoke was getting in the house. So I added an in-line duct fan at the top of the chimney that draws 140 ft.³ per minute through the stove. And then I put that fan on a one-hour timer to coincide with the length of a normal burn. This fan is not meant for regular woodstoves and so has a thermal shut off at 140°F. Nevertheless, my smoke exhaust has always stayed under that number since the fan has never turned itself off due to thermal protection.
I also discovered that I certainly did not have enough air intake for this
rocket stove. It needs quite a bit of oxygen! The hole I cut in the bottom leading to outside air was entirely insufficient for the oxygen needs of the stove. So my very simple but perhaps non-optimal solution was to simply open the front door of the stove and give it inside air in addition to some outside air through the stove floor. Now it runs much better although according to my calculations, for this one hour burn in the stove, it uses about 1600 ft.³ of inside air in the end. Considering that I have 40,000 ft.³ of air in the house total, this 1600 ft.³ can be considered part of the normal air exchanges during the day. It is not what I planned, but maybe I can figure something better out next year. As a side note, I should have scraped or stripped the paint off the first barrel/bell before moving the stove indoors. The first few burns were smelly with burnt paint.
Rocks in the second barrel stack (see pic) helped quite a bit with heat retention, and I put a box fan a few feet away from this stove to carry more heat away through air convection. My worry there was that he was going up the chimney due to the fan too quickly. Temperatures on the first barrel go up to about 600 F during the burn, then come back down. Temperatures on the chimney 10 feet off the floor never seem to exceed 120F.
We now have a system where it seems to work for us. We haven't encountered very cold days yet of course, but these one hour burns of about 8 pounds of dry pine seem to warm up the house fairly well so far. The process is as follows:
- load up the firebox with 8 pounds of dry wood (pine branches, 2x4 cutoffs, etc.)
- open the chimney slide damper and turn on the chimney inline fan on a one hour timer
- put an old iphone to chime in 58 minutes as a reminder to shut things down
- start the fire with a Homeright C900046 fire starter
- leave the door half open for the 58 minute burn
- at the end of the burn, close the chimney slide damper, let the fan turn itself off, shut the stove door
We are very hopeful for a warm winter.