Talk to me about Smoldering

[Mike592]

I've been burning our new Heritage stove for a few weeks now and feel like I've learned a lot. Now that I have a handle on how temps are affected (I have a stovetop thermometer), I'm starting to watch my chimney pipe for when smoke is visible coming out. I understand that's bad and is sometimes the fault of "smoldering".

I know smoldering can promote creosote. How do people avoid it? It seems inevitable to me. Specifically:

1) What do you do on those long overnight burns? Eventually after hours the flames flicker out and there's just coals left to smolder away, right?

2) On overnight burns, it seems like a lot of people turn their air control all the way off. When i do that after a good raging flaming fire, it seems like I get a lot longer burn (wood lasts longer), but the flames wither out quicker and I'm assuming the logs in there "smolder".

3) Maybe I just don't know the right procedures for running my stove, but when I finish burning a load and my stove is up around 450 or so, I let it cool down some before adding more wood. I don't want to load it to the gills again and risk getting too high of temps when that takes off. So while I'm enjoying that 450 degree stove, there are no flames and just glowing coals, until temps come down and I feel comfortable loading it up again. Is this not the right way? Isn't this smoldering?

Thanks.

 

[Mike592]

Sorry one more thing. I'm surprised how often there are visible flames in an already hot stove (375-400) and I see smoke coming out of the chimney pipe. I guess I thought that wouldn't happen so long as there are active flames. Or maybe I don't fully understand why I've read on here that visible smoke is a bad thing.

 

[Dave K]

All of your questions are good and I am curious to learn these things also. Someone mentioned in another thread that once it gets down to coals there isn't any moisture left to create creosote. I don't know though because I am inexperienced too.

I also check the chimney while getting a fire hot and notice some smoke but its not thick and white, it is kind of transparent. I don't know if transparent smoke is as bad?

I noticed that the seasoned wood I had (from the previous owner of the house) would burn with no smoke at all. But thats all gone now and the wood delivery I got a few weeks ago has more smokage than the seasoned wood.

 

[RORY12553]

I have a hearthstone heritage stove. My procedure goes like this: I load the stove completely and have the air fully open. I will then let it burn for a little then damper down a quarter. Let it burn a little more and then damper down to half. Let it burn then damper it down to a quarter. Let it burn some more then damper it down completely. This is done for overnight burns. I usually get about 7 hours out of it and can get it going the next morning again. During the day I will usually load and damper down to about a quarter. In my opinion the wood I am using is well seasoned. I have a "professional" come and clean the chimney once a year and haven't had any issues knock on wood!

I do get some smoke in the beginning of the burn process but that goes away once it gets going. SEASONED/DRIED wood makes all the difference.

 

[RORY12553]

All of your questions are good and I am curious to learn these things also. Someone mentioned in another thread that once it gets down to coals there isn't any moisture left to create creosote. I don't know though because I am inexperienced too.

I also check the chimney while getting a fire hot and notice some smoke but its not thick and white, it is kind of transparent. I don't know if transparent smoke is as bad?

I noticed that the seasoned wood I had (from the previous owner of the house) would burn with no smoke at all. But thats all gone now and the wood delivery I got a few weeks ago has more smokage than the seasoned wood.

Think the transparent smoke is more a vapor or steam! It looks clear?

 

[USMC80]

I think "transparent smoke" is more of a light blueish color as opposed to real thick white smoke from unseasoned wood

The heat signature from the chimney is clear

 

[Backwoods Savage]

I've been burning our new Heritage stove for a few weeks now and feel like I've learned a lot. Now that I have a handle on how temps are affected (I have a stovetop thermometer), I'm starting to watch my chimney pipe for when smoke is visible coming out. I understand that's bad and is sometimes the fault of "smoldering".

I know smoldering can promote creosote. How do people avoid it? It seems inevitable to me. Specifically:

1) What do you do on those long overnight burns? Eventually after hours the flames flicker out and there's just coals left to smolder away, right?

2) On overnight burns, it seems like a lot of people turn their air control all the way off. When i do that after a good raging flaming fire, it seems like I get a lot longer burn (wood lasts longer), but the flames wither out quicker and I'm assuming the logs in there "smolder".

3) Maybe I just don't know the right procedures for running my stove, but when I finish burning a load and my stove is up around 450 or so, I let it cool down some before adding more wood. I don't want to load it to the gills again and risk getting too high of temps when that takes off. So while I'm enjoying that 450 degree stove, there are no flames and just glowing coals, until temps come down and I feel comfortable loading it up again. Is this not the right way? Isn't this smoldering?

Thanks.

It is not necessarily low or smoldering fires that cause creosote. Most of that problem comes from burning wood that is not dry enough. This excess moisture combined with lower flue temperatures will cause creosote.

I've never read of so many running their stoves with the air completely off until this fall. We never do that. Well, one exception. One day my wife forgot what she was doing and the stove top was getting close to the maximum so shut the air off. Wrong! That made the stove top hotter. When I came home to find this, I simply told her to give the fire some air. She about flipped! However, once we gave the stove some air, all was well.

You can let the stove burn without visible flames if you have a catalyst but I'm not so sure that is good practice with other stoves.

Your method of running the stove may differ slightly that someone else who is using the same stove. This is very common so use other folks suggestions as guidelines and not gospel.

450 is not particularly hot stove. However, that is a bit too hot for adding more wood. In mid winter when more heat is needed we will usually be adding wood when the stove top is from 300-350. You stove I believe is a 600 degree maximum. Still I do not understand why you are afraid of loading the stove up if you need the heat. I've seen lots of folks fearing too hot of a stove and burn way lower than they need to just because of fear of too hot of a stove.

For example, the Woodstock stoves have a 700 degree maximum recommended and we find some folks getting excited when they get their stoves to 500 or 550. That is nothing to fear. For sure I did start getting a bit excited when we first got this stove and one night the temperature just kept climbing. While enjoying the heat, after the stove exceeded 650 and was still climbing, I really began to wonder. If memory is right, it topped out at 680. Really gave us a great flame show that night too.

One more thing on burning down the coals. Once we are into mid winter and needs lots of heat, it is common for folks to have too many coals and not enough room left in the stove to add the amount of wood they need. We learned to watch the fire and once it was down to or very close to the all coal stage, we simply open the draft full. That will hold the stove temperature while burning down the coals.

 

[BobUrban]

x2 on pretty much what Dennis has said and there is really no way to burn a solid fuel heater completely without smoke. The goal is to keep it to a minimum but during cold start-ups and refueling smoke is inevitable. If you start with low MC wood and get it all charred real good before shutting the air down you have limited the smoke issue as much as possible and, as Dennis stated, this smoke is not very dangerous. The moisture that is/was in the wood will be mostly burned off and even the little smoke you get is not a problem.

At the tail end of your burn cycle there is really no moisture left so, again, very little worry even if you are sleeping and cannot adjust the air burn the coals down. Open that air all the way first thing in the AM and get the coals going again.

For the record, I burn most of the time with my primary air control completely closed off(or as closed off as the design allows) with no problem but this is likely based on my set-up allowing it. With a full load and air off I get 600+ on the top and complete secondary ignition continuously for hours before full coaling. Sometime I wish I could close off more air. Even with this going on if I go outside I can see a little smoke at times. Others mileage may vary.

As mentioned often on here - for at least the first season with a new stove just check the chimney every month or so and clean if necessary. Not a bad idea to take some notes with MC, dates, ave. temps, etc. This way going forward you will know what is going on in there w/o looking.

Enjoy the heat.

FYI: My definition of "Smoldering" is never allowing the stove to get hot enough to ignite the secondary burn action. Either purposely out of fear it is too hot or due to inferior wet wood.

 

[Bster13]

When I get home I open the air up all the way on my BK to breath another few hours into the heat, then reload b4 bed,

If I let the coals burn down a lot, I just rake them a a bit to uncover them from the ash, but I keep them level. If I have a lot of ash in my firebox, I may rake coals forward to try and burn up as much fuel in the firebox as possible.

Once my wood outgasses, no smoke for the rest of the ride.


I'm not sure leveling or raking coals forward make much of a difference in burn time with my CAT stove.

We learned to watch the fire and once it was down to or very close to the all coal stage, we simply open the draft full. That will hold the stove temperature while burning down the coals.

 

[Sprinter]

1) What do you do on those long overnight burns? Eventually after hours the flames flicker out and there's just coals left to smolder away, right?

Once the wood turns to non flaming coals, the creosote-producing products have burned away, so you can just let the coals burn down at that time without worry about creosote.

 

[begreen]

Sorry to be contrary, but if you have smoke from smoldering the driest wood on the planet, and the flue temps are below the condensation temp of wood gas, you are going to get creosote buildup.

 

[oldspark]

Sorry to be contrary, but if you have smoke from smoldering the driest wood on the planet, and the flue temps are below the condensation temp of wood gas, you are going to get creosote buildup.

Yep well documented and proven in the real world by many chimney fires.
"At temperatures below 250 degrees F creosote will condense on the surfaces of stove pipes or chimney flues.When the temperature gets below 150 degrees F the creosote deposit will be thick, sticky and similar to tar. This tends to trap carbon from smoke which dries and bakes inside pipes and flues. This flaky substance is very flammable"

 

[BrotherBart]

So you can never let a stove full of coals burn down and go out because it will be coating the flue with sote? I dun tink so Lucy.

 

[oldspark]

So you can never let a stove full of coals burn down and go out because it will be coating the flue with sote? I dun tink so Lucy.

That's not what we are saying at all, the gases are gone by then and am pretty sure you know that.

 

[BrotherBart]

That's not what we are saying at all, the gases are gone by then and am pretty sure you know that.

Not at all. There are a lot of gasses coming off of that coal bed. What isn't coming off of it is moisture and that is what condenses on the walls of the flue below the boiling point of water. That is what sticks creo to the pipe. Below 212 degrees, the boiling point of water. Though the humidity from your house sucked into the intake is always going to be going up the pipe.

 

[oldspark]

Nope, are you going to make me post a link to the stages of a fire and the fact there are no gases in the coaling stage.

 

[begreen]

Maybe I am not understanding this but at the charcoal stage the tar gases are greatly reduced. This is why charcoal is used as a fuel still in a lot of Asia.

 

[oldspark]

""The charcoal glows: As the fire progresses and most of the gases and tars have vaporized out of the wood, charcoal remains. Charcoal is almost pure carbon and burns with a red glow and very little flame or smoke. Charcoal is a good fuel that burns easily and cleanly if it is given enough air. Although charcoal combustion produces almost no smoke, the exhaust can have high concentrations of carbon monoxide, so it must be vented completely to outdoors"

 

[BrotherBart]

Nope, are you going to make me post a link to the stages of a fire and the fact there are no gases in the coaling stage.

Nah. Just go up and stick your face in the flue during coal stage. That will answer it. And try to keep it there for more than two seconds. Don't inhale.

Or just look at the heat waves. From the ground.

 

[oldspark]

"Following the release of volatile gases, the

remaining material is charcoal, which burns


at temperatures exceeding 1100° F."

 

[oldspark]

Charcoal burns clean as stated in many places many times.

 

[BrotherBart]

You say gases. What you mean is smoke.

 

[oldspark]

Volatile gases are what causes the creosote so we burn them with our cats or secondary burn tubes or a hot fire and after they are gone you have clean burning charcoal which causes little creosote as the stove cools.

 

[BrotherBart]

By George I think he's got it.

Waiter, check please.

 

[Cynnergy]

Just to add some newbie realism to this thus far very theoretical debate - I can get smoke reappearing in the coaling stage if there's not enough air. Seems to happen mostly when I'm burning smaller fires and not getting temps up sufficiently at the beginning of the burn. Not sure if it's something to do with my wet wood or my stove/chimney system - I'll tell you next year when I have drier wood.