My chimney guy, who's very nice but considers himself the fountain of all knowledge, suggested to me that if possible, I remove the bark from all firewood I burn, unless the wood hasn't seen rain/water for many months. He says that bark acts a sponge, and will hold on to recent water, whereas the underlying wood is slower to absorb (and of course slower to dry). He says this moisture will accelerate creosote in the liner, which I think we all agree on, though I've never seen this particular issue addressed here or elsewhere. I do remember reading somewhere though that bark "contributes" to creosote formation, and so should be removed, though I'm not sure if anyone knows that bark burns any dirtier than the underlying wood. So there's two issues: Does bark hold on to recent moisture more than the hard wood, and does it burn dirtier than the wood?