I burn Bit coal inside now. It's does not fuse together, that is caused from getting too Hott, the coal burning too hot causes it to fuse and make clinkers. The forced blower prolly contributes to that. Bituminous coal has two stages of burn. The first stage it releases a lot of gas which burns. Lots of secondary air helps burn the gas making it more efficent and less smoke, when the gas burns it is very Hott. When burning bit coal the bigger the better. Just small enuff to get in the door. Big peices release gas slower and help prevent fusing. When u use small coal in a hand feed stove and dump over a hot bed a extreme amount of gas is burning off all at once and gets real real hot and smokes like crazy and wastes a lot of potential heat in the gases going up the chimney. Stage two of bit coal is when it turns to coke. At this stage it burns like Antercite coal. Needs all of the air from underneath and won't smoke and glows red and can produce blue flames. It However doesn't burn as hot in the second stage as it does the first, again another reason for big pieces to slowly release its gas. The yellow intense flame is the gas