Gerry Parent wrote:What your describing Nicolas sounds more like a bell or stratification chamber than a piped system for your heat exchanger.
I'm assuming your referring the 30 gallon "bell" is your barrel.
Efficiency can be better in a bell than a piped system as the gasses (hot and cold) don't all flow together but rather have a chance to separate out and release more of the heat before exiting the chimney stack. Bells also don't put any drag on the exhaust so they can maintain better overall draft.
Glenn Herbert wrote:You mention a 4" system. Is this a J-tube or a batch box? J-tubes smaller than 6" tend to be unreliable and hard to use, and one would give a very small amount of heat - not 2/3 of a 6", but probably closer to one third. Batch boxes do scale down, though again the heat output would be less than half of a 6" bb.
Great advice, thanks! I will probably go with something along the lines of a brick box. I have about 4' of this wall built and was at the point of considering ducting, but that's an engineering catastrophe waiting to happen. I will consider draft / combustion air for sure. Probly a few weeks out, but I'll post pics if and when it is successful lol : ) Appreciate all the info on these boards!
Glenn Herbert wrote:A 4" Dragon Heater core should function as well as one that size can, but the heat output will be small enough that I would want to ensure good draft, especially at startup. If the mass gets cold and the outside air is warmer, it might be impossible to start without major smokeback. I would incorporate a bypass that allows a short, direct exhaust path going up, so that the system can be reliably lit. Once going, it may be able to handle some zigzag ducting through a mass. I would definitely go for a hollow brick box rather than a duct running through masonry, though, to reduce drag as much as possible.
A 6" J-tube system is supposed to be good for 35' of horizontal, minus 5' for every 90 degree elbow, so I think a 4" system would be good for no more than 20' of straight run 4" duct, maybe only 15', minus allowances for elbows. In other words, not much length. A bell cavity will have much less danger of friction restricting your draft.
So it takes a day for light to pass through this glass? So this was yesterday's tiny ad?
2021 RMH Jamboree planning thread!https://permies.com/wiki/148835/permaculture-projects/RMH-Jamboree-planning-thread