Here is what I have found out with the SF1000 so far. Do not load it with a good bed of coals when the stat is calling for heat with the inducer running nonstop. You will get the top of the door glowing like your talking about and burn through your wood in no time. Get the load charred with the door cracked and I watch the flue temps around 500 internal. Shut the blower off and let it heat up the house. Turn the blower back on when the temp Is raised to the stat setting. With ash, elm, and oak it holds a flue temp around 300 after that and the inducer does not come on for a couple hours. I can get 4-5 hours when it's below 10 degrees out and I have gotten 12 hours at 35 degrees out over night. At the suggestion of another member I lowered the circulation fan on temp to 140 and it produces heat a good hour longer now. I have a bunch of larger splits, 8"-10" that fit three across with two layers in the fire box once it's going. I am going to check the flue this weekend, calling for 50+ on Saturday. If I see a large creosote issue I'll let you know. Hope this helps. I'm very satisfied with the furnace even though it has some quirks I don't like.