Minimizing Creosote with an Older Stove and a Masonry Lined Flue

[JV_Thimble]

Trying to work out whether I can do a much better job of minimizing creosote with my current setup. I need to do some repair/remodeling either way. Possible options I could consider include:

1. Simple repair of my current configuration.
2. Install of an oval liner, keep current stove.
3. Install of an oval liner, along with a new stove.

Current setup is a 1977 VC Vigilant, with an automatic damper on the intake air. Outlet is just an open or closed flue damper. Simple repair would be to make proper connection through the wall (straight back out of the stove into the flue). Liner is 7" x 12", and extends up a total of 23.5 feet.

I burn reasonably dry wood, as I get about 1/2 myself and buy about half in advance. I burn about 4 facecords a year for supplemental heat. Species vary, but include soft maple, cottonwood, and cherry in what I harvest, and unknown hardwoods in what I buy (denser than the cottonwood). I'd like to think I manage to season the wood for a year on average, though it may be a bit less (that's one area I know I need to work on).

Here's how I typically burn wood, which is where I'm hoping I can make the most improvements:

1. Set up some newspaper, along with some smaller wood pieces, some fatwood, or a wax-coated pinecone and 2-3 larger pieces of split wood.
2. Light the paper. I sometimes/often have smoke coming down the flue at the start, so I crack a nearby door and leave the stove doors open until draft is flowing right.
3. I close the doors on the stove when the fire is burning well, and my flue temperature thermometer is reading 100 F or more.
4. I run the stove with a flue temp reading of >200 to <500 F, based on the color coded zones on the thermometer. Have worked out the position on the automatic damper so that I don't need to mess with it.
5. Add wood as needed to maintain temperature. I generally don't touch the air intake when I do this.

A couple of photos attached that may help.

 

[oldspark]

My older stove was run just like you are doing (flue temps) and never had any creosote to speak of but my chimney is an interior masonary one with only about 6 ft sticking out the roof.

 

[OhioBurner©]

Dads old Vigilant always left a lot of creosote in the chimney, but I think a lot of that was not fully seasoned wood. Could have been a bit of a draft issue as well... It was a triple wall stainless 6" flue.

 

[begreen]

That exterior block flue is going to cool down flue gases quickly when it's cold out. If you can keep the flue warmer with an insulated liner, it should help a lot.

What is connected to the big brick chimney? I was surprised to see the block chimney adjacent to it.

 

[JV_Thimble]

That exterior block flue is going to cool down flue gases quickly when it's cold out. If you can keep the flue warmer with an insulated liner, it should help a lot.

What is connected to the big brick chimney? I was surprised to see the block chimney adjacent to it.

Good question - that's a fireplace upstairs. As near as I can tell from my own observations and talking with neighbors, that end of the house used to be a barn (downstairs) and living quarters (upstairs). My guess is the large chimney and brickwork was an effort to stabilize some settling from a too-shallow foundation. Seems to be pretty stable now, although that end of the house is a bit downhill from the rest. Both the family room (where the fireplace is) and the rec room (where the woodstove is) do not have heat ducts from the natural gas furnace. Whoever set this up must've thought the downstairs would've been warm enough, and found it not to be the case. So, the woodstove and block chimney were an afterthought. At the least, I'd like to get the woodstove chimney functional, and then at least paint it brown to match.

 

[JV_Thimble]

BTW, does it look like my surface-mount magnetic thermometer is in the right place? That kind of thermometer ok?

 

[begreen]

BTW, does it look like my surface-mount magnetic thermometer is in the right place? That kind of thermometer ok?

VC recommended putting the thermometer on the griddle. Any accurate thermometer that can read up to 1000F surface temp should work.

 

[branchburner]

How hot does that mantle get above the pipe, or do you have a shield?

 

[BrowningBAR]

Trying to work out whether I can do a much better job of minimizing creosote with my current setup. I need to do some repair/remodeling either way. Possible options I could consider include:

1. Simple repair of my current configuration.
2. Install of an oval liner, keep current stove.
3. Install of an oval liner, along with a new stove.

Current setup is a 1977 VC Vigilant, with an automatic damper on the intake air. Outlet is just an open or closed flue damper. Simple repair would be to make proper connection through the wall (straight back out of the stove into the flue). Liner is 7" x 12", and extends up a total of 23.5 feet.

I burn reasonably dry wood, as I get about 1/2 myself and buy about half in advance. I burn about 4 facecords a year for supplemental heat. Species vary, but include soft maple, cottonwood, and cherry in what I harvest, and unknown hardwoods in what I buy (denser than the cottonwood). I'd like to think I manage to season the wood for a year on average, though it may be a bit less (that's one area I know I need to work on).

Here's how I typically burn wood, which is where I'm hoping I can make the most improvements:

1. Set up some newspaper, along with some smaller wood pieces, some fatwood, or a wax-coated pinecone and 2-3 larger pieces of split wood.
2. Light the paper. I sometimes/often have smoke coming down the flue at the start, so I crack a nearby door and leave the stove doors open until draft is flowing right.
3. I close the doors on the stove when the fire is burning well, and my flue temperature thermometer is reading 100 F or more.
4. I run the stove with a flue temp reading of >200 to <500 F, based on the color coded zones on the thermometer. Have worked out the position on the automatic damper so that I don't need to mess with it.
5. Add wood as needed to maintain temperature. I generally don't touch the air intake when I do this.

A couple of photos attached that may help.

Few things:

1. listen to BeGreen in regards to the exterior chimney and thermometer location.
2. My stove pipe temps are usually around 180°-300° when burning in horizontal mode. Never even near 500°.
3. I have to question how dry your wood is. Even with the exterior chimney you should not have that much creosote that far down your pipe. Last years wood for me was 'passable'. Meaning; it wasn't as dry as it should have been and I had FAR less creosote build up at the end of my pipe than you did at the beginning of yours.

 

[OhioBurner©]

...and I had FAR less creosote build up at the end of my pipe than you did at the beginning of yours.

Thats makes me wonder, how is cresote normally formed, more at the end or at the start? On my old stove I always notice way more creosote in the single wall and thimble than I do in the masonary chimney. Is that not normal?

 

[CALJREICH]

An old chimney sweep told me to burn short hot fires. Not long smoldereing ones to avoid creosote.

 

[JV_Thimble]

How hot does that mantle get above the pipe, or do you have a shield?

There is no shield, which is part of the reason this needs to be reconfigured. Setup was just single-wall pipe jammed straight back and into the end of the Class A. Reconfiguration would be to extend Class A further out, then double wall pipe to stove.

 

[JV_Thimble]

[/quote]
From BrowningBAR:

Few things:

1. listen to BeGreen in regards to the exterior chimney and thermometer location.
2. My stove pipe temps are usually around 180°-300° when burning in horizontal mode. Never even near 500°.
3. I have to question how dry your wood is. Even with the exterior chimney you should not have that much creosote that far down your pipe. Last years wood for me was 'passable'. Meaning; it wasn't as dry as it should have been and I had FAR less creosote build up at the end of my pipe than you did at the beginning of yours.[/quote]

***

If these are the case, then:

1. I need to line the flue.
2. I would guess that if I ran it cooler, my problem would be even worse. And I'm thinking the thermometer will read hotter if I move it onto the griddle.
3. Agreed, which is why I mentioned it as a possible factor. The wood I have now is very dry, especially as I have nowhere I really want to burn it right now.
4. Need to buy more wood soon, but until I find a way forward with this problem, I'm hesitant to do so (I have about 1-1/2 face cords on hand out of 4 that I would typically burn.)

 

[JV_Thimble]

An old chimney sweep told me to burn short hot fires. Not long smoldering ones to avoid creosote.

I've been told this as well. It's part of why I'm guessing I could make some improvements by somehow burning wood differently. My guess would be to burn hotter. So far, though, I'm getting somehwat mixed messages from the group on this.

That's also why I threw out the three possibilities at the beginning:

1. Simple repair of my current configuration.
2. Install of an oval liner, keep current stove.
3. Install of an oval liner, along with a new stove.

I don't want to go through the expense of a new stove now, but I'm open to the possibility that this one may be over-sized. And it makes a difference in how I reconfigure, as the outlet on the VC Vigilant is 8".

 

[Battenkiller]

JV, I don't see it mentioned at what temperature you close the internal bypass damper. That, to me, is the critical part of burning this stove cleanly. If you close it when your flue temps are only around 200º, you will likely get a long, smoldering burn and a lot of creosote.

I don't look at the thermostatic air intake as "automatic" at all. You should open it all the way (move handle to the left) in the beginning to get the fire roaring in the box, then close the bypass damper only when the fire is fully involved and (for my stove and installation) flue temp is close to 600º for about 5-10 minutes. You should leave the air open all the way to allow the secondary combustion in the back passages to "catch" well (you will hear a dull roaring sound) as the direction of the burn path changes from vertical to a zigzag horizontal burn. Finally, you should close the thermostatic air flapper in stages to allow for the flame path to adjust to progressively less air and to keep flue temps up.

If you can get a great secondary burn going, you can move the lever way over to the right and still keep flue temps up above 300º. I have found that is hot enough to get a clean burn, but cool enough to get an all-night burn with a full load of dense hardwood. My stove cruises at about 600-650º with this method and it will pump out a ton of heat. If it is too much heat for that room, you will have to space your reloads farther apart. Thousands of folks in the past installed that stove in a room too small and gunked up their chimneys by trying to close the air too far down to control it. It can be a clean burning stove or a creosote factory depending on what and how you burn in it.

Also, no matter what VC said in the past, I personally feel that flue gas temps are much more indicative of the way your stove is burning than stove top temps. Best of all worlds has an additional thermometer mounted on the griddle top as BG mentioned. Where you have it mounted right now is way too close to the collar. A 200º temp at that point on a rear exit install is way too cool except at the tail end of the burn.

 

[JV_Thimble]

JV, I don't see it mentioned at what temperature you close the internal bypass damper. That, to me, is the critical part of burning this stove cleanly. If you close it when your flue temps are only around 200º, you will likely get a long, smoldering burn and a lot of creosote.

I don't look at the thermostatic air intake as "automatic" at all. You should open it all the way (move handle to the left) in the beginning to get the fire roaring in the box, then close the bypass damper only when the fire is fully involved and (for my stove and installation) flue temp is close to 600º for about 5-10 minutes. You should leave the air open all the way to allow the secondary combustion in the back passages to "catch" well (you will hear a dull roaring sound) as the direction of the burn path changes from vertical to a zigzag horizontal burn. Finally, you should close the thermostatic air flapper in stages to allow for the flame path to adjust to progressively less air and to keep flue temps up.

If you can get a great secondary burn going, you can move the lever way over to the right and still keep flue temps up above 300º. I have found that is hot enough to get a clean burn, but cool enough to get an all-night burn with a full load of dense hardwood. My stove cruises at about 600-650º with this method and it will pump out a ton of heat. If it is too much heat for that room, you will have to space your reloads farther apart. Thousands of folks in the past installed that stove in a room too small and gunked up their chimneys by trying to close the air too far down to control it. It can be a clean burning stove or a creosote factory depending on what and how you burn in it.

Also, no matter what VC said in the past, I personally feel that flue gas temps are much more indicative of the way your stove is burning than stove top temps. Best of all worlds has an additional thermometer mounted on the griddle top as BG mentioned. Where you have it mounted right now is way too close to the collar. A 200º temp at that point on a rear exit install is way too cool except at the tail end of the burn.

Thanks for the thoughts. Sounds like I need to make some changes to how I work the stove and where I monitor temperatures. I had taken it that since the damper is very open when cold and closes as it gets hot, that it could be used in one position only. But what you're telling me and what I've found here says otherwise - https://www.hearth.com/econtent/index.php/QA_Templates/info/1820/. Sounds good to me - live and learn.

I hadn't realized that secondary combustion was something that occurred with these older stoves, so it will be interesting to work with that. I just found out from Rockford Chimney Supply that my Class A is indeed their brand - Metalbestos. So, I'm now thinking I'll go with my original Option 1 (Simple Repair of my current configuration), and also change where I monitor temperatures, how I burn wood, and push for a larger stock of wood = drier wood to burn. And before my next burn, I'll call out another chimney sweep - even though it was just swept, it's clearly not a very good job (based on simple observation and all the comments I'm getting).

If this works well, great - if not, I need to think about lining the chimney next year.

Many thanks,

John

 

[branchburner]

Thousands of folks in the past installed that stove in a room too small and gunked up their chimneys by trying to close the air too far down to control it.

My family was one of those thousands back in the 70s - took a chimney fire for us to figure it out.

 

[JV_Thimble]

Thousands of folks in the past installed that stove in a room too small and gunked up their chimneys by trying to close the air too far down to control it.

My family was one of those thousands back in the 70s - took a chimney fire for us to figure it out.

Thanks for emphasizing this. When I reconfigure and burn this hotter than before, I need to keep this in mind. Didn't have a problem before (with room temp), but it may be that I was choking it back without realizing it. If that's the case, I may be in the market for a smaller stove for the next season.

 

[spirilis]

The old lady who had my house custom built back in 1981 went along that too, having a VC Defiant II installed when the house was built (rear-vented into a thimble that's just the right height for the stove when it sits on some metal pucks--so it was probably an option provided by the builder) into the upstairs, into a chimney that is 12x12 (WAY too wide) and a flue length that's only about 10ft from Defiant thimble to chimney top. The upstairs is under 800sqft total, BTW, and that stove does not heat the downstairs worth a damn at all even with the heat pump fan running.

Lots of odd, nonsensical design decisions made with my setup that I can only imagine were made for looks rather than function, but in spite of it all, I can still get that Defiant to heat reliably with a small load of wood going at full blast and not very much creosote produced. A little hardened creosote on the bottom of the thimble that I had to break off with a chisel, but the flue swept pretty clean. We get used to a "fire" involving the living room being around 90F with the remainder of the upstairs pushing into the upper 70's and eventually lower 80's. The secondary combustion/downdraft mode on the Defiant doesn't seem to work for us as I never hear that dull rumble everyone talks about and there's plenty of visible smoke coming out the chimney when I do it, but I noticed it does burn consistently (the fire doesn't just go out) and slows/moderates the heat output when I do it. Once I light a fire (with 6 woodbrickfuel in a teepee and a quarter of a supercedar) in updraft mode and get the griddle to the mid-to-upper 600's, flue pipe exit around 450-500F, I can flip the damper and the griddle top will settle to around 450-500F, flue pipe around 290-350F or so. Visible smoke coming out the chimney though. Then again I see visible smoke in updraft mode too--I don't think the Defiant's entire combustion chamber gets hot enough for a thoroughly efficient burn when I'm burning such a small load of wood (approx. 12lb worth) even though the griddle gets so hot. I would never dream of burning more wood than that because the load I use right now already gets the place too hot.

PS- I observe the temps using an infrared thermometer, and the "flue temp" is the pipe's surface temperature taken just 1 inch beyond the oval-to-round adapter coming out the back of the unit.

 

[JV_Thimble]

Once I light a fire (with 6 woodbrickfuel in a teepee and a quarter of a supercedar) in updraft mode and get the griddle to the mid-to-upper 600's, flue pipe exit around 450-500F, I can flip the damper and the griddle top will settle to around 450-500F, flue pipe around 290-350F or so. Visible smoke coming out the chimney though. Then again I see visible smoke in updraft mode too--I don't think the Defiant's entire combustion chamber gets hot enough for a thoroughly efficient burn when I'm burning such a small load of wood (approx. 12lb worth) even though the griddle gets so hot. I would never dream of burning more wood than that because the load I use right now already gets the place too hot.

PS- I observe the temps using an infrared thermometer, and the "flue temp" is the pipe's surface temperature taken just 1 inch beyond the oval-to-round adapter coming out the back of the unit.

I like this tip as well - if the stove heats the room too much, make smaller fires. And burn them hot enough.

 

[spirilis]

Once I light a fire (with 6 woodbrickfuel in a teepee and a quarter of a supercedar) in updraft mode and get the griddle to the mid-to-upper 600's, flue pipe exit around 450-500F, I can flip the damper and the griddle top will settle to around 450-500F, flue pipe around 290-350F or so. Visible smoke coming out the chimney though. Then again I see visible smoke in updraft mode too--I don't think the Defiant's entire combustion chamber gets hot enough for a thoroughly efficient burn when I'm burning such a small load of wood (approx. 12lb worth) even though the griddle gets so hot. I would never dream of burning more wood than that because the load I use right now already gets the place too hot.

PS- I observe the temps using an infrared thermometer, and the "flue temp" is the pipe's surface temperature taken just 1 inch beyond the oval-to-round adapter coming out the back of the unit.

I like this tip as well - if the stove heats the room too much, make smaller fires. And burn them hot enough.

Building small fires can be difficult since there's less wood to heat it up, but I'll hand you a trick that's been working out for me--Add 2 or 3 charcoal briquettes near your firestarter.

Here's my routine (I'm using woodbrickfuel which is similar to BioBricks, but a split 'n kindling analogy might apply)-
I place a quarter of a supercedar in the center, and 1 charcoal briquette (el-cheapo Sam's Club jumbo sized, not match-light btw) on either side of it, then I drizzle some firestarter gel across those 3. I then build the elongated teepee around those (2 pairs of bricks leaning against one another, each pair side by side, then a brick leaning against each end of that), put a slat of pallet wood on top, get the grill lighter between the bricks and ignite the gel, then close the door. With the charcoal briquettes there it develops a VERY hot, bright yellow (almost yellow-white) flame early on instead of a orange/yellow-ish flame. The briquettes are like "insta-coals", lighting quick and helping superheat the smoke so you get the most secondary combustion out of the little wood you have in there.

 

[bjkjoseph]

insulated liner will solve your problem

 

[JV_Thimble]

insulated liner will solve your problem

Yes, I suspect you're right. But I still need to do a better job of burning with the stove, and a liner seems like a lot more work to me. Wouldn't I need to remove the section of Class A that's nicely mortared into the wall now? It's 8", same size as the stove outlet. I figure get the 8" properly set up for this year. If the stove is too big or I'm still having trouble, line it with 6" next year, and get a new stove then.

 

[JV_Thimble]

JV, I don't see it mentioned at what temperature you close the internal bypass damper. That, to me, is the critical part of burning this stove cleanly. If you close it when your flue temps are only around 200º, you will likely get a long, smoldering burn and a lot of creosote.

I don't look at the thermostatic air intake as "automatic" at all. You should open it all the way (move handle to the left) in the beginning to get the fire roaring in the box, then close the bypass damper only when the fire is fully involved and (for my stove and installation) flue temp is close to 600º for about 5-10 minutes. You should leave the air open all the way to allow the secondary combustion in the back passages to "catch" well (you will hear a dull roaring sound) as the direction of the burn path changes from vertical to a zigzag horizontal burn. Finally, you should close the thermostatic air flapper in stages to allow for the flame path to adjust to progressively less air and to keep flue temps up.

If you can get a great secondary burn going, you can move the lever way over to the right and still keep flue temps up above 300º. I have found that is hot enough to get a clean burn, but cool enough to get an all-night burn with a full load of dense hardwood. My stove cruises at about 600-650º with this method and it will pump out a ton of heat. If it is too much heat for that room, you will have to space your reloads farther apart. Thousands of folks in the past installed that stove in a room too small and gunked up their chimneys by trying to close the air too far down to control it. It can be a clean burning stove or a creosote factory depending on what and how you burn in it.

Also, no matter what VC said in the past, I personally feel that flue gas temps are much more indicative of the way your stove is burning than stove top temps. Best of all worlds has an additional thermometer mounted on the griddle top as BG mentioned. Where you have it mounted right now is way too close to the collar. A 200º temp at that point on a rear exit install is way too cool except at the tail end of the burn.

I finally understand your question, after having looked at the manual as was suggested in another post. I've always left it open. So, I need to make more changes than I had thought - I need to re-learn how this thing works (as though I knew in the first place), perform the suggested maintenance, etc...

 

[Battenkiller]

The secondary combustion/downdraft mode on the Defiant doesn't seem to work for us as I never hear that dull rumble everyone talks about and there's plenty of visible smoke coming out the chimney when I do it, but I noticed it does burn consistently (the fire doesn't just go out) and slows/moderates the heat output when I do it. I don't think the Defiant's entire combustion chamber gets hot enough for a thoroughly efficient burn when I'm burning such a small load of wood (approx. 12lb worth) even though the griddle gets so hot. I would never dream of burning more wood than that because the load I use right now already gets the place too hot.

PS- I observe the temps using an infrared thermometer, and the "flue temp" is the pipe's surface temperature taken just 1 inch beyond the oval-to-round adapter coming out the back of the unit.

It must be tough burning those bricks inside the cavernous Defiant. 6 highly compressed bricks weighing a total of 12 pounds sitting in the middle of a big stove designed to hold 65 pounds of cord wood up to 24" long. Your griddle top gets hot because the heat rises to it, but those bricks are a long way away from the face and those sides. Have you tried using more bricks and closing the air down almost all the way? You can close the secondary flap down a bit as well. Seems to me this might give the same heat into the room but burn cleaner due to higher internal combustion temps.

I'm going to pick up a couple sleeves of those bricks to experiment with. I'll try 6 in my smaller stove and see what they do, then try 8-10 and see if I can't keep the same heat output by varying the air a bit. I'll also see if I can get a secondary burn going with them. I like the idea of doing away with a some of the cord wood, even if it costs me more money. I have plenty of room to stack 2-3 pallets at a time in my basement.