Last winter I cut a lot of downed trees that had been on the ground for a while. Several of them were fairly rotten and soft but I didn't realize how bad they were until I split them. They were frozen when I cut them which made them more solid. I stacked all the punky stuff near our fire circle and had planned to burn it outside. Once I realized how much I had, it seemed like a waste not to use it for heat inside the house. I started burning it a few weeks ago when the temperatures got warmer and am pleasantly surprised with the heat output. The wood is dirty but we will get several weeks or more worth of heat out of it now that we aren't burning 24/7.