Log Boilers or Log Gasification Boilers use logs but, unlike a wood burning stove with a back boiler, the gases released from burning wood are re-burnt in a second chamber allowing efficiency levels of 80 – 90%. Log boilers are very cost effective if you have access to your own fuel but the boilers do need feeding on a daily basis and a lot of wood is required so it’s important to calculate storage space required as the logs must be below 25% moisture content – air dried for two to three years.