My Harman TL300 is now in operation for two weeks. I absolutely love this stove. It is easy to control, simple and clean to operate with it top loading feature, and I am absolutely ecstatic about grilling on it. Everything works the way is suppose to work, with one exception. I do not get 12 hours burn time. I do not have any draft issues. The stove is easily controlled by air controls and there is no problem to maintain temperature. The chimney is 22' straight double walled . The house is 2700 sq feet, open plan. It seems hard wood that I bought as being pretty well seasoned and of good quality. There is no visible smoke when I burn the stove in the after-burn mode. The outside temperatures in the last couple of weeks have ranging from 33 to almost 50, and yet I was not getting more then 8 hours of burn time with the full load. Even with the air control almost all way down. Any suggestions?