This is my second year with a Wood Gun E-140 gasification boiler from Alternate Heating Systems. Back puffing has been a problem from the start. I installed a 5" round intake pipe for outside air, which greatly reduces the amount of smoke emitted in the basement, but that's only dealing with the symptom. The chimney is a 6" stainless steel liner with about a 50' run in a century old four story Victorian. The Wood Gun is connected to the chimney with the recommended configuration of stainless stovepipe. If I damp the standard wood stovepipe damper down on the fresh air intake side as far as it will go then it rarely back puffs. BUT, when it cycles on it will emit smoke out the 6" stainless flue side stovepipe that connects the ash collecting "cyclone" with the stainless chimney liner located within the brick chimney structure. There is chimney draft, but I have no means of measuring it. It sucks ash up pretty well. I connected a barometric draft control fixture up to the chimney pipe and, surprisingly, there wasn't enough draft to make the flapper move even when set at the lowest setting, even with the counter weight removed altogether. Perhaps it is worth mentioning that the is a creosote buildup in the air intake inlet (about a 5" round steel pipe) and, sometimes at least, the air intake stovepipe is warm within 6 - 8" of the boiler when the outside air temp is below freezing. I have read some other topics, and have gained the impression that I have a chimney draft problem, perhaps a column of cold air back-feeding into the "sealed" gasification unit that overpowers the thrust of the system's downdraft fan (which also acts to "push" air out to the ash collector/flue pipe. In part, my impression is due to the fact that puffing only occurs when the fire has been out for some time or the firebox has a one-half or more load in it. Any thoughts would be appreciated. In answering, it would be helpful if you defined any abbreviations used. I saw a lot of them in some of the other posts and have no clue what they mean. Is there a post that provides common definitions and acronyms? If not, maybe someone knowledgeable could post one. Thanks for any help.