Hi, I'm New to this coal burning and have gotten my Harman sf 250 fired up a few times. But I'm losing the fire. even when its been burning for hours, it starts to fade from the corners and works its way in. I've tried adding coal but still lose it. tried giving it more air and still lose it. I really want to make this work this winter, but shoveling out unburnt coal out of the box and starting over again is a time consuming pain. I was wondering if there are some tips u guys might have for me. The chimneys clean, using Kimmels nut coal, and have to give it more airflow than what the manual says. Thanks--Joel
P.S. It burns wood real well!