gambler wrote:Damp or wet coal will not flow down a 4" pvc pipe unless it is at an extreme angle..
45 degrees is plenty for aluminum so I'm basing my recommendation on that. However aluminum is more slippery, Terra cotta pipe is probably better than PVC, size of coal is imporatant too. Nut will go down any surface at 45 even if it was sandpaper.
Even the cleanliness makes a difference.
As far as the shut off gate goes you can do that but even a bunch of crumpled up newspapers should work after initial shot of coal is piled against them. Might be an issue getting them in there if bin is full.
syncmaster , what I would do if I was going to build this is not make it final until I had it working. The other thing not mentioned is if this is outside the wet coal will freeze. I'd suggest getting your coal delivered in the spring or early summer and make sure the bin is ventilated so it can dry out. Rice inside a structure will take a while to dry out.