I had my first clinker experience this morning, and I have a question about it. With the cold weather of the night before last, I once again installed my outdoor air supply duct. In an effort to keep the house as warm as possible, I burned the stove fairly hard that night, with stove temperatures of 450-500° on the magnetic stove thermometer. The next morning, I noticed that the area front and center, close to the glass, had burned out the quickest, and at that point was gray. I shook down the grates, reloaded, and last night removed the air supply duct. When I awakened this morning, I noticed the same area was dead. Probing down into this area, I discovered 10 or 12 pieces of apparently fused ash, quite hard and quite light in weight, about 3-4 inches in their longest dimension. The thin layer of fresh coal I had put on top of this area last night had burned. Using my shovel, I dug down to the grates and removed these pieces of fused ash. Then, I filled the hole with fresh coal.
My question relates to why the clinkers formed. It appears obvious that the area of clinker formation, which was closest to the outdoor air supply, suggests that the outdoor air supply had something to do with the formation of those clinkers. After all, there was very cold air (about 17° that night) rushing in through the coalbed right at that area in the front center. Did it have more to do with the coldness of the air, or, because cold air is more dense, was that area of the fire more hot because of increased combustion from the higher air density?
I suspect it has more to do with a hotter fire in that area rather than a colder one, but I would appreciate any insight people here have on this issue. Some background information is necessary: I am burning nut coal, 60 or 70 pounds per day. Filling and loading about every 12 hours.