Intrepid Flexburn--Secondary Burn Is Just Not Happening

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El_Barbón

New Member
Feb 8, 2022
6
Washington State
Hi! We installed a new Intrepid Flexburn in the fall of 2021, and I'm still trying to get a handle on how to operate it to best effect. So first, the background:

When we moved in, the house had an old gas furnace (six-digit phone number in the paperwork!) and a Fisher Baby Bear in the basement. We used the furnace for a month, looked at our gas bill, said, "Huh," and went exclusively to wood heat after that. There's a grate in the floor over where the wood stove sits, and we put a fan in it, open the doors upstairs, and use the stove to heat the basement and first floor. We live in Vancouver, WA, so it gives you an idea of what the climate is like, and we're heating just under 1350 square feet with it. Using the wood stove keeps the un-insulated old house pretty comfortable, and we go through an average of 2.5 cords of wood from October to April, and we used the Fisher for about ten years before getting the new stove. There is a second half-story, with baseboard heat, so it's only important 'cause it makes the chimney taller--close to 28' from basement floor to top.

I *know* chimney height matters, but I honestly did the human-brain thing and just said, "I have a wood stove here, so it'll be fine if I put a different one here!" and we bought the new stove and muscled it into place. The manual with the Intrepid says it's optimized for a 16' chimney, which is obviously not anywhere close to what we have. Still, it seems to draw fine; we have a window that we leave slightly cracked all through the heating season, and the only time we ever get smoke is when we forget to open the damper, open the top when fire's smouldering, or when there's a heavy wind (and even then, it doesn't seem to downdraft once the fire's going). Chimney sweep has never said there's an indication that soot is building up too fast or hard, so we must be doing *something* right. When we started out with the new stove, we had problems keeping the glass clear at first, but have that pretty well dialled-in now, and there's not much build-up to speak of.

Sooooo... what's the problem, then, right? Basically, I cannot for the life of me figure out how to get the secondary burn to reliably work. Last year I didn't install the cat; it didn't arrive until December, and by then, I didn't want to bother with it, since the stove was in use. I did use the damper semi-regularly, and would hear the delightful whoosh of secondary combustion, which would last anywhere from a minute or two up to half or three-quarters of an hour. This year, I put the catalyst in, and I can't get the damn thing to roar almost at all. I'd use the temperature probe that came with the catalyst, except the instructions are utter trash and I have no idea where it's supposed to go. The catalyst also doesn't seem to quite fill its socket. No matter what I do, there's almost always visible smoke (with or without cat), and I'm not getting that secondary burn anymore.

What the heck am I doing wrong? Is the chimney too tall? Am I not getting the stove hot enough--and if not, how can I fix that? I load the firebox up and have it blazing nicely and am getting plenty warm, but is it still not enough? I'm mystified.
 

EatenByLimestone

Moderator
Staff member
I suppose the first thing to check would be the moisture content of the wood you're burning. Do you have a moisture meter? The VC is going to be a lot more finicky about moisture than the Fisher.
 

El_Barbón

New Member
Feb 8, 2022
6
Washington State
I suppose the first thing to check would be the moisture content of the wood you're burning. Do you have a moisture meter? The VC is going to be a lot more finicky about moisture than the Fisher.
I do have a moisture meter... somewhere. :p And it is definitely a picker beast than the Fisher was, but the stuff we're burning has, for the most part, been sitting split for at least a year. While it's not scientific, until I can figure out where the meter went, I've been bringing in wood that is "light for what it is," makes a good sound, and slivers snap rather than bend. Some of it is damper than I'd like, judging by how it burns, but most of the wood we've been using catches quickly and burns smoothly.
 

Woodsplitter67

Minister of Fire
Jan 19, 2017
2,769
Woolwich nj
Id go through your wood stack and do some random testing on some splits. dont test on the ends split it open and test the fresh split face with the pins going with the grain.. youll need 20%mc or below. Im not sure what year stove you have but, the manual is on line and if you have a question regarding a specific stove post it to the vc owners thread. Are you trying to install the factory bimetal probe or a digital one..
 

El_Barbón

New Member
Feb 8, 2022
6
Washington State
Id go through your wood stack and do some random testing on some splits. dont test on the ends split it open and test the fresh split face with the pins going with the grain.. youll need 20%mc or below. Im not sure what year stove you have but, the manual is on line and if you have a question regarding a specific stove post it to the vc owners thread. Are you trying to install the factory bimetal probe or a digital one..
Yep, when I was testing with the meter, it was usually in a freshly split stick. Average moisture content was between 16%–22%. Some of that stuff was *dry*, as low as 10%, so I loaded the woodshed up and tried to mix the oldest and newer stuff together. That might be a bad habit I learned from the Fisher, which would cheerfully burn anything you'd put in it. :p

The stove is from 2021, I've got the manual for it, and it's the factory probe that came with the cat. It's just that the illustration of where to put the probe is donk. But it makes sense to post a separate question for that to the VC thread--thanks!

At this point, I'm going to seriously search for the meter, or get a new one. Since the Intrepid is more finicky about moisture than the Baby Bear was, it sounds pointless to try and pin down any operator error until I can get a definitive answer on how dry the wood is. Just to be clear, though, nobody's said boo about the chimney height. As long as I'm not getting undue creosote buildup, then, height isn't an issue?
 

Woodsplitter67

Minister of Fire
Jan 19, 2017
2,769
Woolwich nj
Yep, when I was testing with the meter, it was usually in a freshly split stick. Average moisture content was between 16%–22%. Some of that stuff was *dry*, as low as 10%, so I loaded the woodshed up and tried to mix the oldest and newer stuff together. That might be a bad habit I learned from the Fisher, which would cheerfully burn anything you'd put in it. :p

The stove is from 2021, I've got the manual for it, and it's the factory probe that came with the cat. It's just that the illustration of where to put the probe is donk. But it makes sense to post a separate question for that to the VC thread--thanks!

At this point, I'm going to seriously search for the meter, or get a new one. Since the Intrepid is more finicky about moisture than the Baby Bear was, it sounds pointless to try and pin down any operator error until I can get a definitive answer on how dry the wood is. Just to be clear, though, nobody's said boo about the chimney height. As long as I'm not getting undue creosote buildup, then, height isn't an issue?

My suggestion is that if your putting a probe in this stove it to put a digital meter on it.. It gives you the exact temperature in real time.. the bimetal thermometer ia a little difficult.. its slow and since its not actually calibrated.. its not as easy.. Aubor at 100 .. look in the vc thread.. bunch of guys just did this
 
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Kevin Weis

Minister of Fire
Mar 3, 2018
1,160
Union Bridge, Md
Hi! We installed a new Intrepid Flexburn in the fall of 2021, and I'm still trying to get a handle on how to operate it to best effect. So first, the background:

When we moved in, the house had an old gas furnace (six-digit phone number in the paperwork!) and a Fisher Baby Bear in the basement. We used the furnace for a month, looked at our gas bill, said, "Huh," and went exclusively to wood heat after that. There's a grate in the floor over where the wood stove sits, and we put a fan in it, open the doors upstairs, and use the stove to heat the basement and first floor. We live in Vancouver, WA, so it gives you an idea of what the climate is like, and we're heating just under 1350 square feet with it. Using the wood stove keeps the un-insulated old house pretty comfortable, and we go through an average of 2.5 cords of wood from October to April, and we used the Fisher for about ten years before getting the new stove. There is a second half-story, with baseboard heat, so it's only important 'cause it makes the chimney taller--close to 28' from basement floor to top.

I *know* chimney height matters, but I honestly did the human-brain thing and just said, "I have a wood stove here, so it'll be fine if I put a different one here!" and we bought the new stove and muscled it into place. The manual with the Intrepid says it's optimized for a 16' chimney, which is obviously not anywhere close to what we have. Still, it seems to draw fine; we have a window that we leave slightly cracked all through the heating season, and the only time we ever get smoke is when we forget to open the damper, open the top when fire's smouldering, or when there's a heavy wind (and even then, it doesn't seem to downdraft once the fire's going). Chimney sweep has never said there's an indication that soot is building up too fast or hard, so we must be doing *something* right. When we started out with the new stove, we had problems keeping the glass clear at first, but have that pretty well dialled-in now, and there's not much build-up to speak of.

Sooooo... what's the problem, then, right? Basically, I cannot for the life of me figure out how to get the secondary burn to reliably work. Last year I didn't install the cat; it didn't arrive until December, and by then, I didn't want to bother with it, since the stove was in use. I did use the damper semi-regularly, and would hear the delightful whoosh of secondary combustion, which would last anywhere from a minute or two up to half or three-quarters of an hour. This year, I put the catalyst in, and I can't get the damn thing to roar almost at all. I'd use the temperature probe that came with the catalyst, except the instructions are utter trash and I have no idea where it's supposed to go. The catalyst also doesn't seem to quite fill its socket. No matter what I do, there's almost always visible smoke (with or without cat), and I'm not getting that secondary burn anymore.

What the heck am I doing wrong? Is the chimney too tall? Am I not getting the stove hot enough--and if not, how can I fix that? I load the firebox up and have it blazing nicely and am getting plenty warm, but is it still not enough? I'm mystified.
What did you do different to get the glass to stay clean? For the life of me I can only get the glass on my Intrepid clean for a few days.
 

El_Barbón

New Member
Feb 8, 2022
6
Washington State
Okay! So, yes, indeed, part of the problem was moisture content. After paying a little more attention to the mix I've been loading, it's doing its thing MUCH better; it seems happier when all the wood is < 18%, as opposed to "probably around 18% or so on average." 😛

Still, though, even when it's chugging along, I'm still getting a lot more smoke coming out of the chimney than I'd expect. Secondary burn is happening, stove is getting nice and hot, wood is burning down to ashes and not smouldering. I gotta figure out how to get that opacity down, now... 🤔
 

El_Barbón

New Member
Feb 8, 2022
6
Washington State
What did you do different to get the glass to stay clean? For the life of me I can only get the glass on my Intrepid clean for a few days.
First thing is I clean it every day. That keeps stuff from building up on it. But mainly, it was just learning how to load the stove so the logs stay far enough away from the front. The little andiron thingies are way too dang small, in my opinion, but if you stack carefully, you should be able to get some space between the glass and the wood. Other than that, it was mainly trying to make sure the air flows through the stack well. I noticed that as the fire burned, you could watch the flames and see how the air was getting channeled; when it was rushing along the front, that's when I'd get the worst soot buildup. Basically, as long as I was keeping the thing from smouldering and away from the glass, I was mostly good. Although... uh, I'll cop to sometimes cheating to get the fire started, and opening the ash drawer a crack to speed things up. I don't do that as much as I used to, now that I've got a better feel for how to build the fire, but I *did* notice that with that rocket going, I'd get a lot more buildup on the windows until I closed the door.

I *will* say, though, that using the cat has made it harder to keep clean, oddly. Some of it comes when I first fire up the stove; I may be flipping the damper too early, and it might not be fully up to temperature even though the secondary burn seems to be happening. But I think most of it comes from the end of the night, when it burns down, cools off, and the damper is still directing smoky air back into the firebox. I do know that once I get the fire going, it seems to burn off some of the buildup, and the glass stays fairly clear until the next morning.
 

El_Barbón

New Member
Feb 8, 2022
6
Washington State
My suggestion is that if your putting a probe in this stove it to put a digital meter on it.. It gives you the exact temperature in real time.. the bimetal thermometer ia a little difficult.. its slow and since its not actually calibrated.. its not as easy.. Aubor at 100 .. look in the vc thread.. bunch of guys just did this
Thanks for that! I'll have to check it out!
 

Kevin Weis

Minister of Fire
Mar 3, 2018
1,160
Union Bridge, Md
I have an Auber 100 on my Intrepid and gives a way better indication of what's going on with the secondaries and the cat. Glad to hear you got it pretty much figured out