Amount of Creosote build up with a cat vs. non-cat?

[53flyer]

Extra creosote formation is usually associated with extended low temp burning right? As I understand, that's exactly the type of burning usually done in a cat stove so I'm wondering if people have experienced more (or less) creosote buildup after using a cat stove? I know the cat's supposed to take care of a lot of it but that's only when it's engaged so I figured there would likely be 2-4 hrs (or so) on the back end of those long, long burns where a lot of creosote could form? Or, have you found they're both (cat & non-cat) about the same irt creosote because by the time they both begin cooling down the wood is burned to the point that there isn't much soot creation in either type? Anyone with experiences using both types irt creosote?

 

[Fsappo]

I've burned numerous non cat stoves, and I've also burned a VC Encore cat and Jotul Firelight Cat. Always use a straight up chimney. None of the stoves I've burned, cat or non cat needed to have the chimney cleaned for at least 3-4 years. And I also never go nuts looking for the perfect dry wood. I just burn whatever.

 

[Pagey]

I would think that the cat would be active during the most important stages of combustion and thus eliminate the bulk of the creosote. By the time the fire has cooled enough to disengage the cat, you're in the charcoaling stage, which is clean burning by its very nature, as I understand it.

 

[Slow1]

Extra creosote formation is usually associated with extended low temp burning right? ...

To be more exact, creosote formation is caused by condensation of smoke produced by incomplete combustion which is associated with extended low temp burning ... particularly in low oxygen environment (i.e. air turned way down)

That's the whole point of the cat - to be able to burn up those dangerous bits at a lower temp so you actually get very close to complete combustion even though the stove is burning at a lower temp and thus using the fuel slower (lower heat output for longer period of time).

Operated in a reasonable manner (don't even have to be perfect from what I understand) with decent wood a modern EPA stove (either cat or non-cat) should minimize creosote formation - certainly far less than older stoves.

 

[Slow1]

I would think that the cat would be active during the most important stages of combustion and thus eliminate the bulk of the creosote. By the time the fire has cooled enough to disengage the cat, you're in the charcoaling stage, which is clean burning by its very nature, as I understand it.

I would agree with this statement - keep in mind though that creosote isn't creosote until it condenses on the chimney (I believe the VOCs and particles have to condense and get a bit of water mixed in - also condensing from the flue gases - to actually create the creosote that sticks to the sides of the pipe). Somewhat of a nit-picky distinction to be sure, but the cat doesn't really burn creosote - rather it burns the VOCs, smoke particles etc. End result is the same - without these ingredients going up the flue you won't have much of anything to condense and create the creosote.

I also would add that a non-cat stove (talking EPA style) reduces emissions by burning the smoke via secondary combustion (albeit at a significantly higher temperature). Note that once the non-cat stove has passed this phase of the burn it too will reach coaling stage and secondary combustion will cease to operate and basically both the cat and non-cat will be burning very much in the same manner. In either case, the VOCs will have been consumed and the coals (basically residual carbon chains) will be burning very clean - mostly CO2, CO and water (the C02/C0 proportions likely a function of the amount of oxygen available to the coals).

 

[Pagey]

I would think that the cat would be active during the most important stages of combustion and thus eliminate the bulk of the creosote. By the time the fire has cooled enough to disengage the cat, you're in the charcoaling stage, which is clean burning by its very nature, as I understand it.

I would agree with this statement - keep in mind though that creosote isn't creosote until it condenses on the chimney (I believe the VOCs and particles have to condense and get a bit of water mixed in - also condensing from the flue gases - to actually create the creosote that sticks to the sides of the pipe). Somewhat of a nit-picky distinction to be sure, but the cat doesn't really burn creosote - rather it burns the VOCs, smoke particles etc. End result is the same - without these ingredients going up the flue you won't have much of anything to condense and create the creosote.

I also would add that a non-cat stove (talking EPA style) reduces emissions by burning the smoke via secondary combustion (albeit at a significantly higher temperature). Note that once the non-cat stove has passed this phase of the burn it too will reach coaling stage and secondary combustion will cease to operate and basically both the cat and non-cat will be burning very much in the same manner. In either case, the VOCs will have been consumed and the coals (basically residual carbon chains) will be burning very clean - mostly CO2, CO and water (the C02/C0 proportions likely a function of the amount of oxygen available to the coals).

Excellent points, good sir knight!

 

[Backwoods Savage]

Extra creosote formation is usually associated with extended low temp burning right? As I understand, that's exactly the type of burning usually done in a cat stove so I'm wondering if people have experienced more (or less) creosote buildup after using a cat stove? I know the cat's supposed to take care of a lot of it but that's only when it's engaged so I figured there would likely be 2-4 hrs (or so) on the back end of those long, long burns where a lot of creosote could form? Or, have you found they're both (cat & non-cat) about the same irt creosote because by the time they both begin cooling down the wood is burned to the point that there isn't much soot creation in either type? Anyone with experiences using both types irt creosote?

You've gotten some great answers. It does appear that you do not completely understand the creosote situation nor the operation of the cat stoves. Even your opening question is only partially correct. That, for sure, is one factor of the equation but certainly not all. The fuel is a bigger factor than extended low burn.

You stated, "I know the cat's supposed to take care of a lot of it but that's only when it's engaged so I figured there would likely be 2-4 hrs (or so) on the back end of those long, long burns where a lot of creosote could form?" The cat is engaged except for the first 10-15 minutes of the burn. This is just to make sure extra moisture is evaporated. Then the cat stays on and keeps working throughout the burn cycle.

You asked if there is more or less creosote with a cat stove and I can tell you we used to clean our chimney twice per year before we got the cat stove. I cleaned the chimney after 2 years using the cat stove and got such a tiny bit of soot (not creosote) from the chimney it was hardly worth doing but I just wanted to see how much we'd get after 2 years.

Now we can get to the real cause of creosote. Plain and simple; it is the fuel that is burned and how that fuel is burned. If people insist on burning only partially seasoned wood, then they will have to deal with creosote. Wood for fuel can not be handled like oil or gas. Wood must have time to dry properly. If it does have this time then you won't have much of a worry about creosote if you know how to operate the stove.

 

[begreen]

Even dry wood has ~15% moisture. I would think that the flue would have to be part of the equation regardless of whether the stove is a cat or not. If one is dumping 400 degree gas into a -10 degree flue, seems there will be some degree of creosote condensation. Or am I in error? Are the cold country burners that have a lot of exposed flue seeing clean flues in spring?

 

[Green Energy]

I know the cat’s supposed to take care of a lot of it but that’s only when it’s engaged so I figured there would likely be 2-4 hrs (or so) on the back end of those long, long burns where a lot of creosote could form? Or, have you found they’re both (cat & non-cat) about the same irt creosote because by the time they both begin cooling down the wood is burned to the point that there isn’t much soot creation in either type? Anyone with experiences using both types irt creosote?

I have a lot of experience burning a large cat stove 24/7. A lot of overnight or "gone to work" packed firebox at 500F, with the air turned down, which slowly drops to a low fire. Over the years, I was surprised at how little creosote I got in my chimney cleaning. I was also using an exterior chimney, 11 x 11, 24' high, with a direct connect that just dumped the smoke above the smoke damper and shelve. The stove had a 8" flue and when I installed it, I knew that it was on the margin in terms of having too much cross section in the chimney. I would usually get about a half a bag (paper grocery bag) of creosote on my annual cleaning. I burned between 2 and 3 cords/year. Usually OK seasoned oak, but sometimes it steamed alittle (less than fully dry). I sure I got a lot more creosote than folks with insulated chimney liners, but less than I expected. I did not think I was endanger of a chimney fire. So was fairly amazed that I did not get more creosote, and it made me a little cavalier about being careful about creosote.

Last winter, early Feb, my 18 year old cat, which was fraying in spots, totally crumbled. I don't think it was working very well most of the winter. I continued to burn for another month with out the cat. When I went to clean the chimney, burning without a cat, with my setup, and the way I burned, was much riskier than I realized. I had major creosote build up. The chimney cap was getting close to closing up with creosote coating the bird screen mesh. I got almost 2 cubic feet of creosote out with my brushing. (Pics to follow). My lesson is that the cat secondary burning is very important to the first and middle part of a burn. Even though the later part of the burn, the cat loses enough temp to be effective, as someone noted, it is in the charcoal stage, so it is not a major producer of creosote.

I now have a full chimney liner, insulated with a good rockwool kit, full block off plates at the top and bottom, and I am burning a non-cat Jotul Olso F 500. Also, I am hoping to be more careful with my wood, burnig better seasoned wood, but probably not super dry. I'll let you know my comparison of creosote after I do my cleaning. I probably will do a mid winter cleaning to be safe.

 

[Backwoods Savage]

Even dry wood has ~15% moisture. I would think that the flue would have to be part of the equation regardless of whether the stove is a cat or not. If one is dumping 400 degree gas into a -10 degree flue, seems there will be some degree of creosote condensation. Or am I in error? Are the cold country burners that have a lot of exposed flue seeing clean flues in spring?

It might be interesting to see what the % is on our wood, but I can tell you it is very dry.

As you know, we do have a cat stove....and we have an exterior SS chimney here in Michigan. I can also tell you our flue never gets to -10 degrees because the chimney is always warm to the touch no matter how cold it gets. And yes, it is clean in the spring.

 

[begreen]

Good to know and impressive!

 

[carinya]

My daughter rents a house in Berea, Kentucky. House comes with a Buck 80. Last year their wood supply was dead stuff that had been lying in a field. Plenty moisture. She said they had bad time with creosote, even with talking to Buck Stoves & having the cat operating at the right temp.

She also mentioned that whenever she turned on the stove fan it would drop the cat temp...

I also think that there is too much stove for the combo of house size and location.

Naturally, I mentioned all the wisdom I have gleaned from Hearth.com & no doubt they have a dry wood supply for the coming season :coolsmile:

 

[Backwoods Savage]

No doubt that dead stuff that was laying in the field was full of moisture. If a log lays right on the ground, it does not take long for it to rot. If it is kept up off the ground then it will keep for quite some time. In this case, it was no doubt full of water. Good to hear they have dry wood this year. They might be lucky if that cat is still working after burning that junk. Water is a big enemy of cats; in the stove or on 4 legs going meow!

 

[summit]

i always see sootier chimney system with CAT stoves... they are tricky to run and sensitive to wood quality.

 

[branchburner]

i always see sootier chimney system with CAT stoves... they are tricky to run and sensitive to wood quality.

In theory, I would think cat stoves should give cleaner flues. But theory is theory... truth is in the observation of actual experience. (Try that line out in the Ash Can and see where it gets you.)

I knew a guy who had no idea his stove even had a cat, so I'm pretty sure he didn't know when to engage it. And of course we always "know" our wood is dry - not. I just burned some "dry" wood last night... still an amateur.

 

[North of 60]

i always see sootier chimney system with CAT stoves... they are tricky to run and sensitive to wood quality.

Funny, I had to clean monthly with the Nap. Probably due to having it turned down so far to stop the runaways and cooking the house out for a few short hours before reload. Now once a year and its really not needed. My woods always 2-3yr seasoned cut from standing dead. Go figure!

 

[Todd]

Most people don't pay attention to proper burning techniques and stove maintenance like most of us here at hearth.com, so i can see where people with cat stoves would have more creosote build up. In my experience I have less build up with my current cat stove than all my previous non cats but I think I'm burning drier wood than I use to thanks to some great tips i've learned here and staying at least 2 years ahead.

 

[Backwoods Savage]

i always see sootier chimney system with CAT stoves... they are tricky to run and sensitive to wood quality.

I wish you could see our chimney. We put up a new one when we installed our present stove, which has a cat. We cleaned it after 2 years use and just got a very little soot and no creosote.

Tricky? Perhaps I haven't learned any tricks yet, but the stove serves us well. When I hear tricky, I think of people saying they want to learn the tricks of the trade. I say learn the trade and forget the tricks.

Sensitive to wood quality? It is me that is sensitive to wood quality. Simply put, I want to know what goes into my stove and I want the best that I have.....and well seasoned.

 

[joe245]

Since we are talking about creosote build up has anyone tried any of the creosote remover products from Rutland or the like. I just installed a wood insert(non cat with S/S liner) They say they are for air tight inserts. Like I said, just put it in a week ago so I haven't checked the manufacturer of the insert or liner. I was not looking for a quick fix if you will but something that I could use to get me to the early spring so I'm not sledging on the roof,if we have snow.

 

[53flyer]

You stated, "I know the cat's supposed to take care of a lot of it but that's only when it's engaged so I figured there would likely be 2-4 hrs (or so) on the back end of those long, long burns where a lot of creosote could form?" The cat is engaged except for the first 10-15 minutes of the burn. This is just to make sure extra moisture is evaporated. Then the cat stays on and keeps working throughout the burn cycle.

Savage- You're saying the cat's engaged the entire time (minus first 10-15) but my understanding is that once the temp gets <500* the cat is no longer engaged (meaning it's not re-burning). Correct? Or, are you considering the "burn cycle" to be over when the temp gets <500 deg?

2 yrs is a long time to have such a small buildup, that's great! Yes, I understand dry wood is a must for less build-up (in any stove really).

Last winter, early Feb, my 18 year old cat, which was fraying in spots, totally crumbled. I don't think it was working very well most of the winter. I continued to burn for another month with out the cat. When I went to clean the chimney, burning without a cat, with my setup, and the way I burned, was much riskier than I realized. I had major creosote build up. The chimney cap was getting close to closing up with creosote coating the bird screen mesh. I got almost 2 cubic feet of creosote out with my brushing. (Pics to follow). My lesson is that the cat secondary burning is very important to the first and middle part of a burn. .

Green- During the cat "dying period" wasn't the smoke staying black (after cat engagement) when the cat was dying? Black smoke is what I've heard is the signal a cat isn't functioning and I'm just trying to figure out if you had warning signs that you weren't getting complete combustion. If you did see black smoke did you ever try operating the stove at a higher temp (higher than you'd operate with a good cat) so the smoke would turn white again (indicating more complete combustion)? I would hope this could be done and basically turn the stove into a non-cat for the period of time until you had a replacement cat and that the creosote problem would therefore not occur. Thanks

 

[Todd]

53flyer,
Once the cat is lit off at 500 it will start to eat smoke and increase in temps as high as 2000 degrees. As long as there is fuel the cat should maintain temps over 500, as the fire dies and turns to coals the cat will cool down below 500 because it no longer has the gas or smoke to burn and there is little or no creosote making particles left. A non cat works the same way but they require a higher internal temp of over 1000 degrees to ignite the smoke and gas so they also need more air and a heavily insulated fire box to maintain those secondary burn temps.

 

[Backwoods Savage]

53, yes, the cat stays engaged until the next reload. Even if the cat is not working at that point, at least the hot air is still circulated through the top of the stove, giving you more heat that it would if the cat was turned off.

Yes, we like those clean chimneys! That is one dirty job that we don't have to do very often now.

 

[Green Energy]

Last winter, early Feb, my 18 year old cat, which was fraying in spots, totally crumbled. I don't think it was working very well most of the winter. I continued to burn for another month with out the cat. When I went to clean the chimney, burning without a cat, with my setup, and the way I burned, was much riskier than I realized. I had major creosote build up. The chimney cap was getting close to closing up with creosote coating the bird screen mesh. I got almost 2 cubic feet of creosote out with my brushing. (Pics to follow). My lesson is that the cat secondary burning is very important to the first and middle part of a burn. .

Green- During the cat "dying period" wasn't the smoke staying black (after cat engagement) when the cat was dying? Black smoke is what I've heard is the signal a cat isn't functioning and I'm just trying to figure out if you had warning signs that you weren't getting complete combustion. If you did see black smoke did you ever try operating the stove at a higher temp (higher than you'd operate with a good cat) so the smoke would turn white again (indicating more complete combustion)? I would hope this could be done and basically turn the stove into a non-cat for the period of time until you had a replacement cat and that the creosote problem would therefore not occur. Thanks

53, I did not really keep tabs on the smoke coming out of the chimney like I should have. I know it would vary depending on where I was in the cycle. Upon heating up with the cat disengaged, I was trying to build temp and I know I was generating smoke. Then I started having a lack of draft, back smoke problem, then I check the cat and it was about 1/3 to 1/2 collapsed. For its age, I was not surprised. I was very happy with the cat technology on this 1989 stove. It served us very well. I was torn about whether to rebuild her and get a new cat.

 

[jpl1nh]

I really never use my furnace, not even in spring or fall. This means I have lots of start up fires from cold starts at each end of the season and thats when I get the most creosote build up, that being repeatedly starting the stove with a cold chimney. Once the stove gets to real 24/7 operating like we should have over the next couple of weeks, there is hardly any additional creosote build up.