I am having a problem with excessive coals when burning hickory. I have a Pacific Energy Vista insert that heats my house just fine when burning oak, maple, cherry and ash. I burn cut slab wood, few pieces over 3 inches thick, most 2 or less. The hickory was stacked in my sunny side yard last April and just covered on the top all summer. This has worked very well for the other species for the last 7 years. The hickory seems very dry and does not spit or sizzle when I put it in the stove. There is no soot buildup on the glass and it appears to burn very clean but the coals that remain are twice what I got with the other woods. The Vista is a small stove and I usually burn with the air fully open and maintain a temp on the side-mounted thermometer of 450 to 550. Do I need to do something different with hickory?