What's the best way to burn wood with the LEAST amount of creosote?

[Eric Johnson]

A little glaze in the firebox and on the glass is normal.

It's probably better to let the fresh pieces catch before damping 'er down, but that really depends on the stove and your burning habits. If doing what do doesn't result in creosote, then I see no reason to change.

Finally, secondary burn is when the smoke coming off the burning wood burns off when it's mixed with the right amount of heat and oxygen. If it doesn't burn, it has the potential to make creosote. In my fireplace, it's easy to see: Smoke becomes flame. Obviously, it's much more efficient and less polluting to burn off the smoke before it gets into your chimney. Most modern stoves do a good job of achieving secondary burn either through mixing the right amount of oxygen, or running the smoke through a catalytic combustor. If you have little or no smoke coming out of your chimney when the stove is up and running, you're doing great.

Creosote, IMO, is nothing to get paranoid about, but it's an important thing to understand and watch for. A little creosote is normal and won't hurt anything.

 

[NewtownPA]

A little glaze in the firebox and on the glass is normal.

It's probably better to let the fresh pieces catch before damping 'er down, but that really depends on the stove and your burning habits. If doing what do doesn't result in creosote, then I see no reason to change.

Finally, secondary burn is when the smoke coming off the burning wood burns off when it's mixed with the right amount of heat and oxygen. If it doesn't burn, it has the potential to make creosote. In my fireplace, it's easy to see: Smoke becomes flame. Obviously, it's much more efficient and less polluting to burn off the smoke before it gets into your chimney. Most modern stoves do a good job of achieving secondary burn either through mixing the right amount of oxygen, or running the smoke through a catalytic combustor. If you have little or no smoke coming out of your chimney when the stove is up and running, you're doing great.

Creosote, IMO, is nothing to get paranoid about, but it's an important thing to understand and watch for. A little creosote is normal and won't hurt anything.

Thanks for the explanation. That does make sense.

Here's another question:
Does "secondary burn" only happen when you reduce the air? (ie, if I keep the air intake open and make a really hot fire, is it producing more or less unburnt smoke than if I choke it off a bit and start to see that combustion inside the firebox)?

 

[Eric Johnson]

It's also called "wood gasification."

I don't know that much about stoves, since I heat with a boiler. But as the fireplace example suggests, the more air you mix into any fire, the more completely it will all burn. The challenge in a woodstove is to control the amount of air to increase efficiency. A fireplace may burn clean, but it's done at the expense of efficiency. Most of your heat (and the heat in your room) goes right up the stack.

I'm sure somebody who uses a modern stove can provide a much better explanation.

 

[tradergordo]

Does "secondary burn" only happen when you reduce the air? (ie, if I keep the air intake open and make a really hot fire, is it producing more or less unburnt smoke than if I choke it off a bit and start to see that combustion inside the firebox)?

No, secondary burn does not only happen when you reduce the air. But the "sweet spot" for your primary air setting in order to get the most efficient burn is very much a stove model specific thing. Less primary air could lead to better secondary combustion, or it could lead to a smoldering (less hot) fire and no secondary combustion. One way to tell is to observe the exhaust coming out of your chimney, if you are getting no visible smoke and adaqute heat out of your stove with the primary air all the way down, then its all good.

I would think full open primary air would lead to good secondary combustion on many models of stove, the increased heat of the fire generally makes secondary combustion work better, but like I said, its a balance, limiting the primary air can make the secondary combustion work better too because there is more unburned gas hitting the secondary burn chamber which can lead to more self-sustaining type secondary burn action with maximum heat where it is most important for efficiency (right where secondary combustion takes place).

 

[NewtownPA]

Does "secondary burn" only happen when you reduce the air? (ie, if I keep the air intake open and make a really hot fire, is it producing more or less unburnt smoke than if I choke it off a bit and start to see that combustion inside the firebox)?

No, secondary burn does not only happen when you reduce the air. But the "sweet spot" for your primary air setting in order to get the most efficient burn is very much a stove model specific thing. Less primary air could lead to better secondary combustion, or it could lead to a smoldering (less hot) fire and no secondary combustion. One way to tell is to observe the exhaust coming out of your chimney, if you are getting no visible smoke and adaqute heat out of your stove with the primary air all the way down, then its all good.

Ok.

So if I reduce the primary air to minimum and I get secondary burn, but it only lasts for about 5 minutes (at which point there are no more flames - just dark red coals), does that mean that I have reduced my primary air too much?

How long should a secondary burn last (should I try to make it last as long as possible by periodically "tweaking" the primary air?).

(I hope you don't mind me asking such basic questions. I'm still learning about all this. )

 

[tradergordo]

So if I reduce the primary air to minimum and I get secondary burn, but it only lasts for about 5 minutes (at which point there are no more flames - just dark red coals), does that mean that I have reduced my primary air too much?

With your stove, yes. If you were talking about an everburn or a catalytic model stove, the answer could be no. You've got "burn tubes" in your firebox, this is where secondary combustion takes place, when you load with wood, you should have visible flames pretty much the entire time until it burns down to coals.

How long should a secondary burn last (should I try to make it last as long as possible by periodically "tweaking" the primary air?).

(I hope you don't mind me asking such basic questions. I'm still learning about all this. )

The secondary burn stage could last for a few hours or longer, basically until all of the wood has turned into coals.
From the manual of another burn tube model stove (quadrafire):

BURNING PROCESS
In recent years there has been an increasing concern about
air quality. Much of the blame for poor air quality has been
placed on the burning of wood for home heating. In order
to improve the situation, we at Quadra-Fire have developed
cleaner-burning wood stoves that surpass the requirements
for emissions established by our governing agencies. These
wood stoves, like any other appliances, must be properly
operated in order to insure that they perform the way they
are designed to perform. Improper operation can turn most
any wood stove into a smoldering environmental hazard.

KINDLING or 1st STAGE
It helps to know a little about the actual process of burning in
order to understand what goes on inside a stove. The first
stage of burning is called the kindling stage. In this stage, the
wood is heated to a temperature high enough to evaporate
the moisture which is present in all wood. The wood will
reach the boiling point of water (212°F / 100C) and will not
get any hotter until the water is evaporated. This process
takes heat from the coals and tends to cool the stove.
Fire requires three things to burn: fuel, air and heat. So,
if heat is robbed from the stove during the drying stage,
the new load of wood has reduced the chances for a good
clean burn. For this reason, it is always best to burn dry,
seasoned firewood. When the wood isn’t dry, you must open
the air controls and burn the stove at a high burn setting for
a longer time to start it burning. The heat generated from the
fire should be warming your home and establishing the flue
draft, not evaporating the moisture out of wet, unseasoned
wood, resulting in wasted heat.

2nd STAGE
The next stage of burning, the secondary stage, is the period
when the wood gives off flammable gases which burn above
the fuel with bright flames. During this stage of burning it is
very important that the flames be maintained and not allowed
to go out. This will ensure the cleanest possible fire. If you
are adjusting your stove for a low burn rate, you should
close down the air to the point where you can still maintain
some flame. If the flames tend to go out, the stove is set
too low for your burning conditions. The air control slide in
the center of the stove, beneath the ashcatcher, is the one
used to adjust the stove for burn rates. This is called the
Primary Air Slide Control.

FINAL STAGE
The final stage of burning is the charcoal stage. This occurs
when the flammable gases have been mostly burned and
only charcoal remains. This is a naturally clean portion of
the burn. The coals burn with hot blue flames.
It is very important to reload your stove while enough lively
hot coals remain in order to provide the amount of heat
needed to dry and rekindle the next load of wood. It is best
to open the air controls for a short while before reloading.
This livens up the coalbed. Open door slowly so that ash
or smoke does not exit stove through opening. You should
also break up any large chunks and distribute the coals so
that the new wood is laid on hot coals.

Air quality is important to all of us, and if we choose to use
wood to heat our homes we should do so responsibly. To
do this we need to learn to burn our stoves in the cleanest
way possible. Doing this will allow us to continue using our
wood stoves for many years to come.

 

[NewtownPA]

tradergordo,

Thanks for the really good info. That helps me understand the process.