The lava rocks self clean by means that they can handle extreme heat, they burn the smoke as it passes through, they do have flyash on the tops of them. But, were the gases pass by they stay clean. Its, quite neat. Locust is the only wood I will burn green. The rocks act as a catch for the creosote, just more place for the tars to stick to, inside the stove. and not the flue. They absorb alot of heat, and can hold it and then release it slowly, my round stove that I took the video of. I have been working with a fire inspector he came over and seen. We filled it up plum full of seasoned black locust, and left the ash door opened the entire burn. The chiminey never got above 500, the skin never got above 700, the lava rock area got up to 1700F. The lava rocks can handle the extreme heat. Backwoods, ifeel your mind is kicking in, I have a provisional patent on the use of lava rocks in a wood burning apparatus, and for incineration purposes. One day my friend, I am more then willing to help with the build of a stove that uses lava rocks. I have videos on youtube, type in lava rocks 44 videos. Good day, its crazy but it works.