Last year I tried using nut in my stone hearth fireplace. I used it as a supplement to the wood coals and it seemed to give some extra heat. Once I had the wood burning good, I would take an ash shovel (the small ones that come in a set with the poker) and put a shovel full in the fire 2 or 3 times a day. It would heat up and glow red and add some heat. It wouldn't burn completely, but when I would start the next fire, I would sort the unburned coal out and start the process over. I'm not sure how efficient it is, but I got some benefit out of it.