I have now tried burning in a woodburner, after Sandyn's suggestion. I use 12" paper bags and fold the tops. One bag per 20+ mins, from a mixture of saw dust and chippings. I'm very happy with it, especially as the bag seems to contain air access and helps reduce any explosive risk.Depends on the stove . Bigger the better and ideally a pyramid shape to give the heap a large surface area. It burns from the top and needs a top air inlet. A tall narrow cylinder or box would be worst option