'Comfortable' Flue Temps...

[Peter B.]

I 'spect there have been countless similar threads, but...

I'm burning in an antique parlor stove that has been retrofitted with an internal catalyst (inside the stove) not far from the flue outlet. The whole setup is unique and likely defies most comparisons to others.

I use a Condar probe thermometer to monitor my flue temps... at 12" above the top of the stove. Again, it's a probe thermometer reading the internal flue temperature, not surface temp.

I also have another monitoring point... immediately above the catalyst *within* the stove.

When the flue temp ranges between 500-600 degrees, the above-catalyst reading ranges (typically) from 800-1000 degrees. (So presumably, I'm dissipating anywhere from 300-500 degrees between the catalyst and the flue probe under those conditions.)

These ranges also (to my mind) represent both best observed heat output and cleanest burn... but actual burn times tend to be fairly short... and there does seem to be a companion price in fuel consumption running routinely at those temps.

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The questions I'd ask are these:

Can anyone here supply an analogous reference using flue temps and upper stove internal temps with an EPA stove?

Or, put another way (more in keeping with the post subject), does 600* and up seem like an excessive flue temperature compared with your (own) stove and flue setup?

And or, do (approximately) similar temp ranges correspond to what you think is efficient fuel use in your own 'typical' experience... or more representative of a situation where you're demanding more output from the stove to compensate for lower outdoor temperatures?

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My gut tells me that I'm sending a fair amount of usable heat up the chimney... and that maybe (next season) I should alter some part of my design to capture more heat from the stove itself.

Overall, I'm more or less happy with the stove's performance, but I'd love to push more usable BTUs out of it...

That is, until I spring for the Pacific Energy model I've got my eye on.

Thanks for your thoughts...

Peter B.

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[WES999]

See my post in this thread for pics of my set up.
https://www.hearth.com/talk/threads/31127/

I set my flue temp alarm at 850*, i figure it is a good upper limit as the flue is rated for 1000* continuous.
When starting up from cold, I let the stove run wide open until the flue temp hits around 800* or so then I reduce the air
then the flue temp drops down to around 450* 550*

 

[begreen]

You are going to get very different results from a modern EPA stove and even then it will vary from stove to stove. With our old Jotul 602, 600 degree flue temps were not unusual. Occasionally they would get up to 900. But with the T6 600 is about the highest I've seen. And as the stove gets into secondary burning most often the flue temps go down, yet the stove surface temps rise. With the Jotul F400 450 deg. was about as hot as the flue got.

 

[RonB]

I typically run my stove so that stack temps are around 250-350 degrees. If mine ran consistently at 600 like yours does I would be allowing too much heat up the stack. Are you able to adjust your primary air any more or is it already closed?

 

[Peter B.]

Thanks for the replies...

After reading some recent posts on the same theme, it doesn't look like (even) a steady state of 600* in the flue is _necessarily_ excessive... regardless of the type of stove.

All the same, it sure would be nice to 'grab' some part of that heat, rather than lose it up the chimney.

I've read of ridiculously long runs of black pipe used in 'olden times' to make use of the available exhaust heat, but I'll bet - even if the stoves were burned flat out - creosote buildup was still a factor and an occasional clean up and/or chimney fire were both realities.

I guess I'll stick with what I've got... above the stove proper, that is. Even with a simple chimney, brushing/sweeping can be a pain mid-winter, and I'd rather not complicate things.

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By the way, on a side topic, older stoves often had 'underfire' and 'overfire' air intakes, and it's not always easy correlating that with modern stove design and practice.

I used to consider the underfire control on my stove the primary air... and the overfire draft the secondary... but on the old stoves the overfire air was seldom if ever preheated... which I guess makes for a distinction of sorts.

In any event, yes, if I close both under and over fire controls, I can get the stove to behave... and slowly drop from any extreme temp... but I also have a supplementary (preheated, overfire) air intake that keeps the fire happy when the other drafts are clamped tight.

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So many variables in this game... I guess that's what keeps it interesting.

Peter B.

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[danking49]

For whatever it's worth, our Quad Millenium 2100 cruises along regularly at 600-650 in the flue 18" above the stove.
I rather lose a little heat up the chimney than risk building excessive creosote and all the potential problems that brings.

 

[begreen]

By the way, on a side topic, older stoves often had 'underfire' and 'overfire' air intakes, and it's not always easy correlating that with modern stove design and practice.

I used to consider the underfire control on my stove the primary air... and the overfire draft the secondary... but on the old stoves the overfire air was seldom if ever preheated... which I guess makes for a distinction of sorts.

In any event, yes, if I close both under and over fire controls, I can get the stove to behave... and slowly drop from any extreme temp... but I also have a supplementary (preheated, overfire) air intake that keeps the fire happy when the other drafts are clamped tight.

Was this stove designed to be a coal/wood burner or just wood? Below the grate air supply is required for coal burning.

 

[Peter B.]

BeGreen:

I think the stove was intended for either wood or coal. It's unclear to me whether there was originally a special grate for burning coal. I'm inclined to think the wood grate wouldn't be of much use for coal... too difficult to shake.

I believe the underfire air supply is common to most antique stoves whether built for wood or coal.

I've been using the underfire draft recently to maintain a hot fire (in preference to the unheated overfire air)... but as mentioned, I also have a (minimally) preheated supplementary intake.

Peter B.

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[Todd]

My internal stove pipe temps range from 400-600 and that's 18" from the stove collar. Sounds like you have an interesting setup. Does your cat have access to secondary air? If not it may not be living up to it's full potential? Maybe there is a way to rig a small pipe with valve near the cat for secondary air to help out? Also might help your burn times if you place a round steel plate over your grate to seal off that excess air from coming up the ash dump. I did this years ago with my old pot belly and it increased my burn times 50%.

 

[DrivenByDemons]

Man these temp threads drive me nuts... I was having problems with to much draft(cause of 30ft chimney)/high temps/short burns and put a damper in (I have a PE spectrum). I took a flue temp reading 5 minutes ago with one of those really accurate tru-temp thermometers and am seeing close to 900F. That's with a 3/4 full firebox, good quality oak, and the damper completly shut and air control all the way down. That 3/4 full load was put in around an hour ago and was charred for about 5-10 minutes. HOW IN H*LL ARE YOU GUYS GETTING SUCH LOW STACK TEMPS????? I feel like I'm wasting half my heat right up the damn chimney. Sorry if I'm hijacking this thread. I just need a good answer on how to get this thing under control.

 

[Todd]

Man these temp threads drive me nuts... I was having problems with to much draft(cause of 30ft chimney)/high temps/short burns and put a damper in (I have a PE spectrum). I took a flue temp reading 5 minutes ago with one of those really accurate tru-temp thermometers and am seeing close to 900F. That's with a 3/4 full firebox, good quality oak, and the damper completly shut and air control all the way down. That 3/4 full load was put in around an hour ago and was charred for about 5-10 minutes. HOW IN H*LL ARE YOU GUYS GETTING SUCH LOW STACK TEMPS????? I feel like I'm wasting half my heat right up the damn chimney. Sorry if I'm hijacking this thread. I just need a good answer on how to get this thing under control.

Pipe damper or rig your air supply mechanism so it can be shut down more.

 

[DrivenByDemons]

Yea, I did the pipe damper already. It's as closed as it will go. I really hate to mod this stove but I'm thinking closing that air control a little more would surely help... Might have to get out the grinder and cut that stopper out a little. Anyone else here modify a PE stove???

 

[Peter B.]

Todd wrote:

>My internal stove pipe temps range from 400-600 and that’s 18” from the
>stove collar. Sounds like you have an interesting setup. Does your cat
>have access to secondary air? If not it may not be living up to it’s full
>potential? Maybe there is a way to rig a small pipe with valve near the
>cat for secondary air to help out? Also might help your burn times if you
>place a round steel plate over your grate to seal off that excess air from
>coming up the ash dump. I did this years ago with my old pot belly and it
>increased my burn times 50%.

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Todd:

At one time, I rigged a secondary air feed for the catalyst... but basically all the mods I've ever made to my stove have been 'prototypes'... and the added catalyst air didn't survive... only because - if I recall correctly - it wasn't well thought out and came apart.

It's hard to burn nearly 24/7 and implement useful, lasting modifications at the same time.

I replaced the original grate years ago with a design of my own that works better for me, but (with this stove) I still find the availability of underfire air useful, and would not want to blank it off entirely.

Meanwhile, in the deep freeze here this week in SW Wisconsin, I'm trying to better my usual wood burning routine, which I confess can be sloppy at times... and leads to reduced heat output and wasted fuel.

My burn times seem to vary a lot. I've seen 12 hours from reload to available startup coals overnight, but that's rare... and at that, I wake up to 40* to 50* indoors. Daytimes, when it's cold out, I'm not doing much better than 2 to 3 hours of good heat output between reloads.

When all is said and done, I'm inclined to think the changes I've made have improved safety and control more than efficiency and spotless burns.

But I'm content with that... at least until I think up the next 'killer' mod.

Peter B.

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[Todd]

I thought about finding an old potbelly to tinker with, they have that old fashioned charm you can't find with most new stoves. You may not want to cut off that lower air but from what I read here air fed from beneath is designed for coal and burns wood too fast and furious. In my old Wards potbelly I put a 1/4" round plate of steel over the grate and used furnace cement to seal up the edges. I kept about an inch of ash in there and it held a good coal bed overnight continuously. That's the only mod I did, never thought of a cat or baffle. Does your stove have a baffle with the cat and some sort of bypass? It would be nice to see some pictures.

 

[Peter B.]

DrivenByDemons wrote:

>Yea, I did the pipe damper already. It’s as closed as it will go. I really
>hate to mod this stove but I’m thinking closing that air control a little
>more would surely help… Might have to get out the grinder and cut that
>stopper out a little. Anyone else here modify a PE stove???

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DBD:

I've allowed myself a free hand with my own 'pre-fire-dragon' stove, but I'll bet (at least until you start a new thread on the topic) there will be few here that will pipe up and encourage you to modify an EPA stove.

Just the same, if you've tried a flue damper and the problem is actually determined to be an overdraft, then I would hope some PE owners might muscle in here and advise you what you might do... there's sure to be a remedy.

I have my eye on a PE 'Fusion', in part because it's (visually) about 180* off from my current stove.

What PE are you burning with?

PB

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[DrivenByDemons]

DrivenByDemons wrote:

>Yea, I did the pipe damper already. It’s as closed as it will go. I really
>hate to mod this stove but I’m thinking closing that air control a little
>more would surely help… Might have to get out the grinder and cut that
>stopper out a little. Anyone else here modify a PE stove???

-----

DBD:

I've allowed myself a free hand with my own 'pre-fire-dragon' stove, but I'll bet (at least until you start a new thread on the topic) there will be few here that will pipe up and encourage you to modify an EPA stove.

Just the same, if you've tried a flue damper and the problem is actually determined to be an overdraft, then I would hope some PE owners might muscle in here and advise you what you might do... there's sure to be a remedy.

I have my eye on a PE 'Fusion', in part because it's (visually) about 180* off from my current stove.

What PE are you burning with?

PB

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I've got a PE Spectrum. I've read the "Florida Bungalow Syndrome" article and I'm convinced it applies to me. One of the remedies for the FBS problem is a pipe damper, which I've done, but I still get that raging secondary with crazy hot flue-gas temps that I feel are too hot and are wasting my BTU's. I know your supposed to burn hot but 900F flue-gas temps with the air control shut completly down is simply too much if you ask me. Of course, it is -3F outside and pretty windy tonight but I've got good wood and pretty decent sized splits and it still ramps right up even with the air down. I've checked for leaks, did the dollar bill test, nothing wrong that I can find. The chimney just sucks like a $2 you-know-what and I can't slow it down.

 

[Peter B.]

Todd wrote:

>I thought about finding an old potbelly to tinker with, they have that old
>fashioned charm you can’t find with most new stoves. You may not want to
>cut off that lower air but from what I read here air fed from beneath is
>designed for coal and burns wood too fast and furious. In my old Wards
>potbelly I put a 1/4” round plate of steel over the grate and used furnace
>cement to seal up the edges. I kept about an inch of ash in there and it
>held a good coal bed overnight continuously. That’s the only mod I did,
>never thought of a cat or baffle. Does your stove have a baffle with the
>cat and some sort of bypass? It would be nice to see some pictures.

I'm afraid I (partly) hijacked the thread pointed to below, but it might (all) be of interest to you... that is, if you hadn't stumbled over it as yet...

https://www.hearth.com/econtent/index.php/forums/viewreply/300761/

Again... decent pitchurs (as well as ongoing mods) are difficult when burning the same stove nearly full time.

Next spring maybe...

--

Interesting idea limiting the only intake air to the (above fire) door (?) intake... but it must have been a bear to get a fresh fire burning, yes?

Peter B.

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[Todd]

Dang it, I missed that thread. Very interesting and simple design mod. You should start a new thread with these mod details. Many people here are always looking for ideas to improve their pre EPA smoke dragons.

As far as my old stove, I'm pretty sure it had two air controls, one on the bottom ash dump and the other on the loading door. Sometimes I had to crack the door to get a fresh load going, but it didn't take but a few minutes and she was roaring. This old stove wasn't as good looking as yours. It looked like a modified potbelly with a large donut heat exchanger on top instead of the ordimental removable top. It was also missing the legs and just sat on the basement cement floor. I was renting the house so maybe the owner put the thing together?