Douglas Alpenstock wrote:Fresnel lenses are fun! And I'm keeping my eyes open for a big one to play with.
They don't offer an energy freebie though. They can concentrate solar energy, but it's exactly the same amount of energy that falls on a simple pane of glass of the same physical dimensions.
That's quite à possibility. What other cause i could see, with such a short chimney. Opening a door, where hot air escapes by the door as well as the chimney. The csa of the door being bigger, it might reverse the draft, with that stubby tube out of the roof.
Glenn Herbert wrote:The OP said on her facebook thread that there is 4' of chimney above the nearly flat roof. It is not tall, but would be adequate in otherwise good conditions.
She also said that the wood (a few sticks) burned fine for ten minutes, then finished burning, went to coals, and started reversing and smoking back.
I think there was insufficient fuel to heat up the system, and when the flames making the draft went away, the heat from the coals took the easy way straight up out of the feed.
Gerry Parent wrote:For a fan forced draft in a pellet stove, 5” would work just fine. For a passive draft RMH, no way. This manifold area needs to be quite large as it is the transition area where the exhaust gasses are switching directions. Too much friction in this area will definitely slow or even stall the stove.
A 10” (or 8” min) diameter pipe outlet reduced down to your 6” would work much better.
Glenn Herbert wrote:You definitely want to be burning as hot as possible, and generally that means fast. A batch box is designed to burn at a steady rate while combusting as completely as possible; Peter van den Berg's tests have generally run for around an hour for a 6" unit.
I don't think I would extend the exhaust duct any farther into the bench cavity. Flow will be sedate enough at that distance from the core that I think you will get good stratification in the bell and maximum heat extraction without more duct.