Also known as back puffing, backpuffing, woodgas explosion
Symptoms are:
Smoke coming out of your wood stove or insert - often in a single PUFF, but sometimes as a series of puffs (like a train steam engine - puff, puff, puff)
This is caused by the delayed ignition of a buildup of combustible gases inside the stove.
At the time of these flashbacks, there is not enough oxygen in firebox and probably too much fuel....or at least too much in a certain stage of burning (initial stages).
Instead of burning steadily, the gases build up and ignite in a small explosion, forcing smoke out of the stove through every available opening, including the air intakes, seams, pipe joints, window gaskets, etc.
Some hints and tips on causes and solutions of flashback:
Causes:
Generally, shutting the air controls down too far AFTER a new loading, starving the fire of oxygen, AND:
Using very dry wood, like pallets or kiln-dried wood blocks, which burn very rapidly, emitting too much combustible gas too quickly.
Using wood that is split very small, which also burns too rapidly, creating an excess of combustible gas in the firebox.
If the flashbacks occur when you are loading the stove, then you are not properly timing your loads and preparing the stove for loading. See solutions below.
Solutions:
Just knowing about the problem goes a long way toward solving it. Once you put some of the ideas here into daily practice, flashbacks should be rare or non-existent.
Mixing less seasoned or larger pieces with the very dry and small split pieces.
Don't stuff the stove full of wood when you are doing attended burning. Over loading a stove will often make you shut down the air control too low. Too much fuel and not enough air can cause flashbacks. Instead, load firebox 1/2 full and burn stove with plenty of air. Keep a flame on the fire.
Please note the comments below from our Forum member Robbie:
Stove puffing smoke after loading wood and dampering down.
Wet or dry wood, it does not seem to matter.
The reason for this I have learned are the gases coming from the wood as it is burning needs to be burned, if you
Damper and choke your stove, or starve your stove of oxygen, then when it does get enough oxygen, the result will be a mini explosion, a small fireball within your stove is the result.
This fireball or mini explosion results in expansion within the stove, which causes the puff of smoke to exit your stove.usually in the weakest place it can find to release pressure (pipe, stove seams etc.).
Fix: After loading your stove with wood, always let it char or burn wood for at least 15 minutes, maybe even longer, and do not damper your stove all the way closed, this will enable your stove to get enough oxygen to burn a little, this will keep gases from building up. As a general rule, I always make sure I can see a steady small flame somewhere in my stove before I leave it for bed or whatever. If there is a flame, then most likely you will not build up any gases because this flame is burning the gases.
Related Forum Threads:
http://www.hearth.com/econtent/index.php/forums/viewthread/10143/
http://www.hearth.com/econtent/index.php/forums/viewthread/3857/
