11 months later: In my case the puffing is not about the wood being to dry or two small but rather the rate of combustion. If I load the stove to the absolute top with large wet wood over a real hot layer of wood that is almost turned to pure charcoal and is burning really well and clean, the new load will begin to catch fire and if my air damper is anything but closed it will start to violently back puff. If I close the damper the puffing is just about stopped and all is well. This happens most noticeably on very cold nights. The fuel in the fire chamber just seems to be igniting the gases within the chamber creating small gaseous explosions that leak out around the door seals and out of the intake air tube. So I can run the boiler with the air damper fully closed and there doesn't seem to be any bad effect from doing so. The outside air temperature creates differant draft and fuel burning characteristics that do take time to learn how to adjust the draft to these conditions. If I burn smaller loads on milder days I can run my damper open more than half way, but I almost never run it wide open. I absolutely love the long burn times I get and the best thing I can say is that I am burning far less wood than ever before and I've been heating with wood boilers for more than 40 years and this wood gun is the best I've ever owned. PS. I don't work for or have anything to do with this company. In fact I bought my SS140 from someone who had to move and had bought it from the Alternate people who make it. I've owned more than three other types of wood boilers and there is nothing out there that compares to this unit.

I have owned an E140 stainless woodgun for about 11 years and I do experience these problems also and not only when the combustion chamber is full. I have found that restricting the intake helps as Caleb mentioned. Split wood that is stored in a woodshed for an extended period of time will definitely "back-puff". It usually does not last very long, however if the unit has any (air) leaks at all the smoke will come out of those open joints as the combustion cycles from low to high in a rather dramatic fashion. It really sounds very similar to a steam railroad locomotive albeit not as loud. Since my unit is indoor I have taken several measures to make sure any smoke that is released is recycled to the intake and thereby recombusted. I do not have any experience with the other two items Caleb mentioned but I have a sneaking suspicion that if you plug one of the two holes in your furnace your BTU rating will suffer quite a bit. I really like the idea of the air diffuser but I am not sure how easily it is retrofitted into older units.

I've been using wood fired boilers all of my life and presently own a SS140. The back puffing only happens when I fill the firebox to maximum capacity for an all night burn. My combustion air is supplied through a 6 inch pipe ducted from outside . I realize that the puffing happens when the gases in the fire box attempt to ignite within the fire box due to excess fuel being in the fire chamber. I think that the Wood Gun is the most efficient boiler I have aver owned and the best part about it is it produces no creosote in my three story chimney. Every other wood boiler that is not a gasification type seems to make creosote. The Wood Gun does not, at least for me. My wood for next year has been split to a much larger size and I'm hoping that will help reduce the puffing. I don't understand why plugging one of the heat exchange tubes would prevent the pre-combustion in the firebox but I am going to call for the diffuser set up and try that. It seems logical that it may cause more of the combustion air to be present in a larger area of the firebox and help with the puffing. Of all the people I know with all the different "gasification" boilers that are out there I think I can say without prejudice the Wood Gun is one of the most efficient and most controllable wood boilers ever built. Puffing is a small price to pay for all of the other positive attributes of these units.

Why does it look like there is a reducer on the exhaust flue pipe or is that something else? Is the bottom half double wall or some special type of pipe since it is super shiny then there is that connection between standard pipe that looks like a reducer?

I see that there is a new digital controller on the side of the this unit. Do you still offer the non digital controls version?? I’m planning on buying a E180 in the near future.