Creosote production through the night?

[Franklink]

Help me conceptualize what is happening throughout an overnight burn.

I understand with these EPA stoves, a hot fire is necessary to burn as much of the gases/particulate produced by a given firebox load of wood to maximize heat production and minimize environmental pollution. From what I can gather from the stove manual, my thermometer, and this forum, if the stove is operated at lower temps, then creosote production is a possibility. So, if I get the stovetop temp up to 400-600 and close down the damper about 30 minutes after the stove is lit (per stovetop thermometer readings) will I be producing creosote for whatever portion of the night my temps are lower than that magical ideal operating temp range?

In my mind I'm trying to plot out creosote production over an x, y graph with the y axis being temperature of stove (as a surrogate for creosote production) and the x axis being time. As the temperature rises, holds, and then decreases am I producing creosote during the rise and fall of temps? For example: If the stove is only above the bottom threshold of non-creosote production temperature for the time frame coinciding with 15 minutes after the fire is lit to 3 hours after damper is closed down, am I theoretically producing creosote from 0-15 minutes and from 3 hours to 11.75 hours?

This question is stemming from the fact that I still had red coals this morning 11.75 hours after I last loaded it with wood. The manual says max burns of 9 hours. Did I close the damper too much and produce creosote for much of the night?

(Stove is a Napoleon 1400C and wood is mostly Ponderosa Pine cut from dead/down trees with much of it being past its prime/punky. Wood is so dry that dust flies when hit with splitting maul. I don't want to give the Pine-Paranoia bunch any ammunition by burning my house down.)

 

[Woody Stover]

I guess there is a curve of creo production over time. It would probably start high after initially lighting and drop off as the secondary system lights off, somewhat leveling into a slow fall as the load progresses, and less and less volatiles are available. As the load coals, of course, less particulates are produced. There's no "non-creo" temp...it's always going to be giving off something, until the coals go out. As far as your x,y time/temp plot, that would rise from the beginning, peak, then fall. Maybe there is some kind of x,y,z graph where you could plot temp, time and creo on one graph, I don't know.
But to your main point, if you close the air too much, you may kill secondary combustion, the load will smolder, and emissions will be higher than they could have been. As long a secondary combustion is occurring, some particulates are being burned. To maintain the optimum clean burn throughout the cycle, air adjustments would probably have to be made along the way. Weather you cut the stove air too low, too soon, and curtailed the clean burn prematurely for that long burn, I don't know. You could set up some sensors at the top of your stack, do so some experiments and report back when you have the results.

 

[xman23]

Being an engineer, I understand you quest to understand the dreaded creosote production cycle. There are other factors. Wood condition being the most important. My first few years my chimney cap was a gooey mess. The glass was blackened every night. Now dusty black stuff and rarely clean the glass. Why, I do burn better, but the wood is seasoned. When you can, initially burn hot to heat the stove and chimney. Then let it go through the burn cycle, cooling down before the next reload. If you don't need heat let it burn out, don't smolder the new wood reload. If you had a bed of coals 11 hours you did good. The test to see how your doing is to clean the chimney after some period of time.

 

[Nick Mystic]

In my experience creosote production is most closely tied to the moisture content of the wood being burned. The wetter the wood the higher the creosote buildup. On my Jotul F600 I can close down my air control fairly quick with wood in the 12 - 18% moisture range and maintain a good secondary burn. However, once the secondary burn dies back I find it best to go ahead and open the air control back up to promote a full burn at hotter temperatures. The secondaries won't necessarily start back up, but the fire in the box will burn better. I tend to monitor my stove pretty close and make adjustments on what I see, rather than just set it and forget it.

 

[firefighterjake]

Moisture and low temps are the primary causes of creosote.

There is bound to be some creosote formation when you first start a fire from a cold start as the fire temp is too hot and the wood may have some moisture in it being "driven off" by the heat.

With a secondary burner type stove once you bring the stove up to temp you dial back the air to achieve secondary burning -- this has the effect of reburning the smoke and the combustibles in the smoke which results in a cleaner and more efficient burn. If the temp is good and the air setting level is fine (I usually wait anywhere from a half hour to an hour before going to sleep or leaving the home to make sure the temps are stable) the secondary burn should sustain itself for several hours until it reaches the point where the fuel load is reduced along with the heat at which the secondary burn no longer works . . . but at this point any moisture should be pretty much eliminated and while the lower temps could produce some creosote, the effects should be negligible.

That said . . . I'm not a scientist . . . just a dumb firefighter who likes to play with fire.

 

[Franklink]

You guys have helped me make better sense of it. I was jumping to the conclusion that zero creosote would be produced if the temps are perfect. That was conflicting with my notion of the obvious rise and fall of stove temps. I was trying to understand how it could be possible to maintain the perfect temps throughout a burn cycle, seems the consensus is that combustion inherently produces byproducts (chimney/pipe buildup) and the goal is to produce as little as possible, but zero-production is not possible. Unless I have absolutely dry wood and I'm willing to stay stove-side, popping Xanax and pacing back and forth in front of the stove 24/7 to make sure I reload it as soon as my stove-top temp drops below a certain point, zero-creosote production is unattainable. Even with perfectly timed reloads, I would still have some minor buildup in the pipe from what you guys are saying. Makes sense too, I just needed to mentally approach it from a new perspective, provided by you guys. (I don't take Xanax and I'm not concerned enough about this to have anxiety, just trying to learn

I also appreciate the suggested idea that most (if not all) of the residual creosote-producing moisture in the wood should be gone by the time the stove temp drops back below "ideal" sometime in the wee hours of the morning. That is reassuring.

Thanks all.

 

[branchburner]

In my mind I'm trying to plot out creosote production over an x, y graph with the y axis being temperature of stove (as a surrogate for creosote production) and the x axis being time.

As others mentioned, that concept is missing other key variables, including the potential amount of unburnt creosote-producing particulate that might condense on your liner, along with the amount of moisture. After all, the reason temps fall late in the burn cycle, assuming good secondary combustion, is that most of the fuel has already been consumed. Even though flue and stove temps may drop, the coaling stage should produce far less creosote because it is producing far less smoke and particulate, with the earlier out-gassing stages of the burn having already turned all that particulate into heat. Even if you have some coals and a warm stove at 8, 12 or even 16 hours after lighting off the load, the potential for particulate is approaching zero because, well, the amount of fuel has been virtually reduced to zero.

I would pay attention to flue temps rather than just stove temps, too. It is possible to run a creosote factory by having what seems to be a hot-enough stove with a too-cool chimney. This is often the case with pre-EPA "airtight" stoves and with flue setups feeding into an oversized and/or uninsulated exterior chimney. So another variable is WHERE in the chimney creosote might deposit, since high-enough temps where the gasses exit the stove don't always mean high gas temps at the far end of the chimney. It probably would not be uncommon for some to get most of their creosote forming in the (much cooler) upper few feet of the venting.

 

[Franklink]

I've only had 6-8 fires but out of curiosity I figured I'd check out the cap at the top of the pipe, luckily its very easy to access. Anyway, nothing but some black soot on the underside of the cap. Was running out of evening light and forgot to take up a flashlight or my phone so I couldnt see inside of the pipe that well. I did, however, place my hand inside and ran my fingers against the inside of the pipe, about a foot down. There is no discernible (to the touch) buildup of anything (no gritty, lumpy, etc.), it just feels like smooth pipe in there. I did have some black on the tips of those fingers though. I know its probably beyond too early to have much buildup (OCD much), but as easy as it was to check, I'll just scramble up there every few weeks.

 

[CheapBassTurd]

Post #8.

I was really worried about this too at first. Only have 4 burning months' experience.
I went up and flashlighted a few times. Clean every time excepting the top one foot or so.
Inside the cap too was a bit of flaky soot. Bought a brush and ran it down to the firebox a few times
just to start with a shine this year too. I'll probably brush monthly. OCD or not, there's children, a wife,
pets we love, and this is our home. The chimney will remain in a state of cleanliness, period.

CheapNotStoopid

 

[JA600L]

Is your liner insulated?

 

[Franklink]

I'm not sure on the nomenclature but I think a liner is the term used when talking about chimneys? My set-up is that of a typical free standing stove: double wall black pipe inside the house, and stainless on the exterior (roof).
(Sorry, I dont have any pictures of the exterior)

 

[branchburner]

One way to further put your mind at ease (or not) is to observe what's coming out of your chimney over the course of a few daytime burns. If the wood is dry and secondary combustion is proceeding well, the only time you should see visible smoke is during startups (and reloads). As a full load goes through an entire burn cycle, the lack of smoke indicates fairly complete combustion and a low likelihood of significant creosote accumulation.

You can also rest assured that a very light buildup of creosote, over weeks and months, does not mean you are in imminent danger of experiencing a chimney fire. If you are burning clean, or even MOSTLY clean, you'll be fine. The guys who need to worry are typically producing gallons of creosote, not just cups worth.

 

[xman23]

I've only had 6-8 fires but out of curiosity I figured I'd check out the cap at the top of the pipe, luckily its very easy to access. Anyway, nothing but some black soot on the underside of the cap. Was running out of evening light and forgot to take up a flashlight or my phone so I couldnt see inside of the pipe that well. I did, however, place my hand inside and ran my fingers against the inside of the pipe, about a foot down. There is no discernible (to the touch) buildup of anything (no gritty, lumpy, etc.), it just feels like smooth pipe in there. I did have some black on the tips of those fingers though. I know its probably beyond too early to have much buildup (OCD much), but as easy as it was to check, I'll just scramble up there every few weeks.

Yep, sounds like you got it understood. My first year, first month the cap screen was plugged with this gooey black creosote. The cap is cold so it doesn't stay as clean as a warm chimney. My screen had to go. The issue was I was burning 8 month old oak. For the first year check your cap and top of the chimney on a regular basis. In few weeks to a month you will know what your producing. It will be just about the same all the way down. Most of us get away with once a year cleaning. When I clean in the fall, I get about two quarts of small black chips and dust. Because it's the same every year, during the burn season I don't look at it at all.

Relax, enjoy the heat and fire view.

 

[Nick Mystic]

I don't like the idea of removing the rain cap screen in order to burn wet wood because I think the clogged cap is a good early warning sign letting you know your flue probably needs cleaning. My stove never lets out smoke during reloads when my system is clean. However, as soon as my screen starts to get any creosote buildup on it I'll notice a little smoke coming out of my stove door when I reload. I know right away my cap is getting clogged and needs cleaning. Without such a warning it would be easy to forget to check your flue and you could get a dangerous buildup of creosote in it.

 

[Vikestand]

My screen gets clogged yet when I go to clean the stack it hardly produces a thing. Few times a winter I get on the roof and inspect the top of the stack and scrub the screen.

 

[jscs.moore]

In my experience creosote production is most closely tied to the moisture content of the wood being burned. The wetter the wood the higher the creosote buildup. On my Jotul F600 I can close down my air control fairly quick with wood in the 12 - 18% moisture range and maintain a good secondary burn. However, once the secondary burn dies back I find it best to go ahead and open the air control back up to promote a full burn at hotter temperatures. The secondaries won't necessarily start back up, but the fire in the box will burn better. I tend to monitor my stove pretty close and make adjustments on what I see, rather than just set it and forget it.

Good points Nick! I'm new to wood burning, just starting my second season but I agree with your technique of opening the air control back up after the secondary burn dies down. I tried to follow the set it and forget burn cycle (I have a Hampton HI300 non-catalytic insert by the way) almost everyone on this site espouses, but seem to get more out of the burn cycle when I follow your technique of opening the air all the way once the secondary burn dies down and I'm getting close to the coaling phase. I guess so many say to follow the set it and forget burn cycle because they are probably burning catalytic stoves/inserts?? Anyway, glad to hear I'm not the only using this technique.

 

[branchburner]

I tried to follow the set it and forget burn cycle ... but seem to get more out of the burn cycle when I follow your technique of opening the air all the way once the secondary burn dies down and I'm getting close to the coaling phase.

I don't see anything wrong with this, and it seems it would help assure minimal creosote, but I think it is also pretty easy to get minimal creosote WITHOUT opening the air all the way up at this stage. I would think the main reason to follow this procedure would be to keep the heat output at a higher level in colder weather.

 

[jscs.moore]

I don't see anything wrong with this, and it seems it would help assure minimal creosote, but I think it is also pretty easy to get minimal creosote WITHOUT opening the air all the way up at this stage. I would think the main reason to follow this procedure would be to keep the heat output at a higher level in colder weather.

branchburner...yes, I think you hit the nail on the head. I started opening up the air intake all the way (after the secondary burn died down and fire was near coaling phase) when it was really cold. I was definitely able to keep the stove temps higher (and the house warmer) by doing this so it has become habit now. But I'm sure your are correct, there is probably minimal creosote at this stage so definitely not necessary to open the air up at this point in the burn cycle. thanks for the feedback

 

[xman23]

I don't like the idea of removing the rain cap screen in order to burn wet wood because I think the clogged cap is a good early warning sign letting you know your flue probably needs cleaning. My stove never lets out smoke during reloads when my system is clean. However, as soon as my screen starts to get any creosote buildup on it I'll notice a little smoke coming out of my stove door when I reload. I know right away my cap is getting clogged and needs cleaning. Without such a warning it would be easy to forget to check your flue and you could get a dangerous buildup of creosote in it.

Nick, I agree, keep the screen if you can. That first year was 16 years ago. I didn't know the unseasoned oak was the problem. I just knew there was know way the screen was going to work that year. The screen was 1/4, way to small. The chimney always looked fine. It took 3-4 years before the cap got better. I'm not saying the screen serves no purpose, but I not spewing chunks of burning cardboard out of my chimney.