Post by patamos on Oct 4, 2016 8:34:34 GMT -8
I've tried two different chimneys. For the first one I actually hooked it into the system I was hoping to heat. Which is about a 12ft horizontal run of chimney pipe through the middle of two short cinderblock walls. (the plan was eventually to fill that space with some kind of mass, rocks, dirt, maybe even cob when it gets warmer, etc.) At the end there's a tee where I primed the chimney and a 10ft piece of vertical chimney pipe tied into the tee. There was a little steam coming out at the far end, really lazy-looking. I figured it might not be drafting enough, so I redid the chimney with just a short horizontal 8ft piece of pipe coming almost directly out of the core, and then I took some of the chimney pipe and made about a 16ft vertical stack. That definitely drafted better, with little to no visible smoke after a few minutes, but I think that's mostly because there's still a good bit of smoke coming back into the greenhouse.
Vortex:
for a door I'm just using a thin sheet of steel with a flange around the outside so that it fits into the door (it's a baking sheet actually). It's not air tight by any means, but i was under the impression that the core would still run even if it weren't totally sealed. Obviously if i had a good seal, I wouldn't have a problem with smokeback except for when I opened and closed the door since the smoke couldn't come out during normal operation. I didn't want to go through the effort of actually making a door for it until I knew it worked, and from the videos I saw it seemed like success was being had with just a piece of ceramic glass leaning against the door.
Cheez, i think the smokeback is due to a combination of many small contributing factors. When the negative pressure 'pull' of heated gases wanting to rise out of the flue is less than the positive expansion pressures in the burn chamber the negative pressure plane within your greenhouse will cause it to act as the chimney. The manner in which gasses are escaping around the door also effects the turbulence patterns in the fire chamber which may be adding the the reverse flow effect.
Insulating your vertical flue stack will help a lot. Widening any turns in the flue runs… Start up bypass, As Matt suggests, working backwards with these kind of little changes will help find the sweet spot.
