I put 20 lbs of lump in and one lit chimney on one side and it warmed up quick. It hovered around 260 for the first hour and then spiked to 318, I shut the damper on the smoke stack. After 10 minutes of a lot of white smoke backing up, the temp crashed to 250 and stayed there for the next six hours. So I had 7 hours of sustained heat. After seven hours I pulled the plug and went to the bed. I can't wait to get some meat on it. And NEVER NEVER buy thermometers from Walmart.