I was browsing here and caught a couple threads where people were asking about puffing with various kinds of wood. A little discussion about the cause of this might be helpful so I'll share what I know about it. Puffing.....the woof woof woof woof you hear and the tell tale smoke coming out around the door is caused by an incorrect fuel to air mixture/ratio. If you would take a flue gas sample during the time the puffing is occuring you would find that CO (carbon monoxide) is "off the chart". It will be extremely high while the excess air/O2 levels will be very low. Simply put, this means that you have an oxygen starved situation in your combustion chamber. There is not enough air to properly burn the fuel available. What is actually happening inside the firebox when any wood burner starts to puff is that the fire is partially going out due to lack of oxygen and reigniting when more fresh air comes into the firebox. It's basically a mini explosion every time you get a woof or two out of the unit.Understand that when you get into a puffing situation your efficiency is going to go downhill rapidly. I have seen about every kind and/or type of wood burner puff but good loading practice and consistent wood will do a lot to alleviate the problem. The basic fact of nearly all wood burners.is that once you reach maximum air input you can do nothing other than decrease the fuel load available. Even the Lambda controlled units will puff if there is more fuel than there is air to combust everything. The exception would be a burner that is set up to control primary and secondary air independently of each other and is able to vary those settings in real time throughout the entire burn. (This is what Tom Caldwell has done with his highly modified Garn) So...........what's a guy to do? Since most of us are not able to sit around and monitor the entire burn we have to be careful about loading density along with being judicious with the small stuff and extremely dry stuff we load. If a person has a lot of smallish wood like 2-3" diameter sticks or fine splits, or one is burning scrap dimension lumber such as 2x4 or 4x4 stuff, he is just going to have to load less of that in at one time, and make sure to mix it with some bigger stuff. Puffing can also occur if you have exceptionally dry wood. And by that I mean a moisture content of 15% or less. I have to say that in my travels I have rarely found anyone using wood in that range because it just about takes 3 years worth of seasoning in at least a semi controlled environment. Wood size and type is a far more common cause than being too dry. Be careful about increasing air to eliminate puffing at the start of your burn because unless you are there to dial it back once the peak part of the fire is past, you;ll be running way too much O2 and losing a lot of heat up the stack. It's best just to learn what size and type of wood your burner can handle and try to not go past that point.