I posted something similar awhile back but it went in the wrong direction. So I've experimented some since with various woods and found what appears to off gas the least so far giving the same air intake is Black Walnut and Mulberry. Ash seems the worse for this then Red Oak. The main difference in the wood structure that I can see is that Ash and Oak are open grain woods and I'm assuming the open grain lets the gasses escape more readily. If I get a puff back it seems it's always with the Ash/Oak not other woods. Stove is a VC Encore soon to be replaced with the new flex burn Intrepid. Just an observation. Feel free to comment or not.