The last stumps I burned were oak and about 35" across. I built a fire on top of them then when it got going really good I took a 15' long piipe and attached it to the hose on our Electrolux vacuum cleaner. With the hose in the blower hole and the pipe aimed at the spot on the stump I wanted to burn I kept at it for quite some time. It took about 16 hours to get it all burned up.