we looked into this. you need to keep them dry as poss but not too dry and good air circulation. Cover them in rainy weather to keep the rain off but don't keep them covered if its dry. The idea is that wet wood (green or sappy) doesn't burn well.Neither does wood that has been rained on. If you leave the wood covered and don't let it dry out then it will begin to rot. rotten (punky) wood burns really quickly and catches fire well but has had a lot of the calorific content taken out of it by the rotting action so isn't as good for heat/energy production or decent slow burning