I have a C450 insert and my dad has a F500 freestanding. Mine top vents through a 2 story chimney and his vents out the back to a 2 story chimney. He can turn his burn WAY down so he gets a lower heat and longer burn time. My C450 insert never seems to slow down much when I move the damper all the way to the left. I've checked it and the lever and damper are still connected so functioning. The gaskets have been replaced on the double doors. Does anyone have any thoughts on why I can't slow my stove down that much? I have to fill it with logs about every 2 hours because I'm down to coals. If I stuff it at night I can still have some coals in the morning but I thought I'd get a longer burn than the 2 hours on my logs (all 1-2 year old split oak/maple' hardwoods)