Heater worked great out of the box. Puts out 231 degree heat. After measuring the fuel use with the heater running flat out for 24 hours, the heater put out a little over 17K BTU which is about what the 5K units should put out. If it was a 8K unit, it should have used a lot more fuel for a 27K BTU unit. After talking to a part supplier on another website for these heaters, he verified there are no actual 8K units, just 5K units sold at a much higher price. Bottom line, save your money and order the much cheaper 5K heaters.