This conversation makes me wonder -- are their other ways to increase heat transfer without the complexity (and possibility for leaks) entailed with cross-tubes? We know that most of the heat we generate goes up the stack rather than into the water, so anything we can do to grab some of it before it heats up the smokebox would be desirable.
The first thing that comes to mind is quills, like a "porcupine" pot-boiler. These would be similar to cross-tubes in that they would pierce the center flue, so they wouldn't provide any siphoning, but they would not carry water themselves so should be less prone to leaks. I have also seen chat about "turbulators", stainless steel strips twisted into a spiral and shoved into the front end of the flue to slow gas outflow (and presumably increase heat transfer to the flue wall). I think quills, arranged in a spiral or "x" pattern, would probably function on a similar principle, but since they're directly connected to the flue (and extend into the water), one would expect the heat transfer to be much greater. I'm sure there are many other ways to slow flow and add surface to increase heat transfer. For example, "corrugations" inside the flue. Cutting rings of a tube the size smaller than that flue, then soldering them into the flue at intervals, would add somewhat to the surface area as well as producing some turbulence inside the flue. Or twisting copper wire into a spiral and soldering it into the flue. I'm sure their are other ways to accomplish this. As Jim mentioned earlier, there's a point beyond which "slowing flow" becomes "blockage", so some experimentation would probably be in order. Does anyone else have ideas or experiences in this area? -vance- Be careful how you live; it is the only sermon that you preach. William Ellery Channing
