ijd,This morning I pulled all the old out, because there were lots of little (hole blocking size) pieces in there. I put the biggest new pieces on the bottom, then the medium sized ones, then I put the old, mostly little ones, on the top. Sure helps keep the holes in the grate free to draw air.Also I noticed that although I always re-use the un-burnt lump, it never really burns as good as it did when it was new, so I try to watch what per cent of each I use.Hope that helps.