Just did a little experiment for shits & giggles with the Jotul downstairs. Used the Jotul because it has glass so I can see what's happening. I do know that whenever I burn the Jotul with pallet wood only, at some point during the warmup period the glass gets completely *black*, or at least 3/4ths pitch black. Eventually as it heats up that all burns off but it happens consistently every time. Lots of smoke outside too. Just lit up the Jotul with 6 woodbrickfuel and 1 short slat of pallet wood on top--the exact same configuration I always use in the Defiant upstairs. The stove glass did darken, but, it did not get pitch black--more of a caramel color with streaks of slightly darker caramel. Consistent flames, and I gotta say, the smoke coming out of the chimney, while it is there, it's fairly low in volume compared to the massive clouds of smoke I used to see billowing over the front lawn when I used pallet wood only. That probably says the most about the difference. I'm guessing the pallet wood, being both light/not very dense and VERY DRY, pyrolizes way too fast to burn alone while the woodbrickfuel is both dense (and probably doesn't burn quite as fast--think hardwood? although the woodbrickfuel came from hardwood sawdust too) and has more moisture than the pallet wood. The mfr. said it's around 6-9% moisture and I guess lumber is lower than that, although I don't have a moisture meter to check. But anyway, that little experiment says a lot. I have run kiln-dried hardwood through the Jotul before but I can't say that experiment is a good comparison because I always used pallet wood to start the fire, then added the kiln-dried on the reload. The glass would go pitch-black during startup and then once a good sized split of kiln-dried was loaded, it'd stay black for a while and then burn off once the outside of the split began to form coals.