# Flue temperature ideology - 300*F - 350 *F how many people think this is too cold?



## pault123 (Mar 10, 2015)

So after reading creosote gets burnt off at 500*F, I figured if I run my stove hot all the time i'll avoid its build up at all in the first place! So my ideology seems to be "get the stove to 480-500 *F " then reduce air so it cruises along at this temp. Missus must think I've lost the plot, as I fettle the stove until it reaches this temp, and only then i'll sit back and enjoy the fruits of my labour 

She thinks this is far too hot and always runs it between 300*F - 350*F (using less wood as a bonus)

So what are your personal flue temperature ideologies, and would you class 300-350*F as too cold as although its in the flue thermos "optimum" range, its not in creosote burning range?


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## brad wilton (Mar 10, 2015)

your doing it right from what i can see


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## jeff_t (Mar 10, 2015)

If that's a magnetic thermometer on single wall pipe, she's right. Internal gas temps are generally double the surface temp.


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## brad wilton (Mar 10, 2015)

480 to 500 and then let it cruise still in safe range no?


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## Grisu (Mar 10, 2015)

That temp close to the stove does not tell you that much in regards to burning clean. You need at least 250 F all the way to the top to avoid water condensation and creosote formation. Depending on how tall your flue is and how well insulated what you have may be enough, wasted heat, or not sufficient. In the long run, you can compare your usual flue temps to the amount of creosote accumulation by spot checking your chimney to close in on the "ideal' temperature.


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## huauqui (Mar 10, 2015)

pault123, could you clarify for us, are you asking about flue temps or stove top temps?

I very well could be wrong but I personally like to burn my PE Summit so that the stove top temps get up to or above 600 and hold there for an hour or two before they go down to around 500 where it seems to sit for awhile before very slowly going down to between 250 and 300 when I reload and repeat.  I don't worry about the flue temps to much as long as I see that type of burn cycle. I saw a very similar burn pattern for our fireview only the top end temps were not as high, I liked it to see about 550 for the upper end of the burn cycle then it would do the same as the Summit and slowly work back down to 250-300 for reload.  I do monitor flue temps and did notice on the fireview the flue temps were noticeably lower then the Summit, maybe a hundred degrees lower during any point of the burn cycle with comparable stove top temps. 

I find my flue temp probe is used more to keep me from over firing then to worry about creosote though I do watch them fairly closely.   

Can't wait to see what others are doing in regards to this.  I am new to these EPA cert stoves and love to learn.

I should add that I am a nut about visual inspection and cleaning of the chimney and do find with those temps I stay pretty clean.


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## Highbeam (Mar 10, 2015)

It's not so much the burning temperature of creo that you are trying to maintain but the boiling point of water. You want the skin of your flue to stay above 250 to be sure that none of the smoke/water condenses. This is creosote.

The temperature of the stove is not an accurate measure of the flue temperature.


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## pault123 (Mar 10, 2015)

jeff_t said:


> If that's a magnetic thermometer on single wall pipe, she's right. Internal gas temps are generally double the surface temp.



It is a single wall flue pipe, so would that mean a 400*F reading on the thermometer, would be 800*F gas temps? Although as the thermometer would be calibrated for this purpose the temps are still safe?


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## Highbeam (Mar 10, 2015)

The "best operation" zone on that meter is appropriate. Over 250 to prevent creo and under 500 which corresponds to 1000 degree internal temps which is the overfire temp for most chimneys.


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## pault123 (Mar 10, 2015)

huauqui said:


> pault123, could you clarify for us, are you asking about flue temps or stove top temps?
> 
> I very well could be wrong but I personally like to burn my PE Summit so that the stove top temps get up to or above 600 and hold there for an hour or two before they go down to around 500 where it seems to sit for awhile before very slowly going down to between 250 and 300 when I reload and repeat.  I don't worry about the flue temps to much as long as I see that type of burn cycle. I saw a very similar burn pattern for our fireview only the top end temps were not as high, I liked it to see about 550 for the upper end of the burn cycle then it would do the same as the Summit and slowly work back down to 250-300 for reload.  I do monitor flue temps and did notice on the fireview the flue temps were noticeably lower then the Summit, maybe a hundred degrees lower during any point of the burn cycle with comparable stove top temps.
> 
> ...




Hi Huauqui, 

Flue temps, with magnetic thermo stuck on around 18" above the stove. (i've got another thermo on order from amazon for the stove top though)


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## brad wilton (Mar 10, 2015)

from what i understand a lot of heat goes up flue at initial start up so that would give a high flue temp before you start to shut primary air after that more heat stays in box bringing flue temp down ?


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## pault123 (Mar 10, 2015)

Highbeam said:


> It's not so much the burning temperature of creo that you are trying to maintain but the boiling point of water. You want the skin of your flue to stay above 250 to be sure that none of the smoke/water condenses. This is creosote.
> 
> The temperature of the stove is not an accurate measure of the flue temperature.



Great post thanks, so in fact even running flue temps as low as  250 *F - 300*F would be adequate to stop smoke/water condensing. I feel a lot better about the other half running at 300-350 *F now    and not as fixated with getting the stove to 480*F every burn LOL


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## Oldman47 (Mar 11, 2015)

Don't be so quick Pautl. If you can maintain at least 250ºF at the top of the flue you are just fine. If you know what temperature you read at 18 inches above the stove when you get that temperature you have something to judge by. It will definitely not be 250ºF flue temperatures at that point but could be that value outside a single wall because the inside and outside temperatures are not the same. Who knows until you establish a value for your own flue pipe that gives you satisfactory non-condensing conditions at the chimney cap. If you think you have it right, go outside and look at your cap. If you see steam coming out of the flue you are a bit cool but if you see it show up a few inches away from the cap you are golden. It means it took those few inches of travel to cool the flue gas enough to form tiny water droplets and it was not condensing inside your flue.


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## begreen (Mar 11, 2015)

Our flue runs with a probe thermometer on double-wall pipe typically in the 400-500F range. That is actual the flue gas temp. The chimney is pretty clean with gray powder at the top. This is what works for our setup. It's a straight-up 20 ft chimney with a good portion inside a conditioned space. If this was a single-wall connector going thru a wall thimble into an outside chimney my results might be different. There is much more opportunity for cooling down the flue gases with that setup. Single wall pipe radiates off flue gas heat pretty quickly. Add say 20ft of exterior chimney in cold winter temps and there is likely to be more accumulation.


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## Poindexter (Mar 11, 2015)

The true test is what your sweepings look like.  If you are getting grey/brown powder out, with a few specks of shiny black in it you're doing pretty darn good.


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## jb6l6gc (Mar 11, 2015)

I wouldn't trust those magnetic thermometers as far as I can throw em...


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## Johnny_Fiv3 (Mar 11, 2015)

jb6l6gc said:


> I wouldn't trust those magnetic thermometers as far as I can throw em...



Ummm, wait. Those things are pretty small and one could really whip one a good distance...

So you really trust them then!


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## jb6l6gc (Mar 11, 2015)

Johnny_Fiv3 said:


> Ummm, wait. Those things are pretty small and one could really whip one a good distance...
> 
> So you really trust them then!



Oh crap I guess so ... Lol. Just got off nights. Don't trust em mine reads off for sure to my it ir gun. I just marked the sweet spot with a paint marker lol


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## gyrfalcon (Mar 11, 2015)

pault123 said:


> Great post thanks, so in fact even running flue temps as low as  250 *F - 300*F would be adequate to stop smoke/water condensing. I feel a lot better about the other half running at 300-350 *F now    and not as fixated with getting the stove to 480*F every burn LOL


I was using a very small Hearthstone Tribute soapstone stove my first three or four years burning, and it's like pulling teeth to get this stove over 400, and wouldn't stay there long when it did get up that high.  It cruised at 350, so spent most of the time around that temp or lower.  I also had plenty of low-temp crappy, smoldering fires from insufficiently dry wood when I was first learning.

I never had more than a couple of cups of powder creosote from my chimney cleaning, and the cap has so little staining, the chimney sweep is still dubious that I actually do run the thing 24/7 during the winter.

That said, I have a new insulated stainless steel chimney and superb draft, which is pretty much ideal for clean burning.  You don't say what your chimney is like, which would make some difference, but is almost certainly still fine.  When in doubt, spend the money to clean the chimney after a month or so, and what's in it will tell the story for you.


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## DougA (Mar 11, 2015)

I just don't think there is an 'optimum' range for wood stoves unless you break it down into cat/non. cat/ etc., then break it further into sizes.  If you are comparing the creosote buildup vs temps, you then have to take  into account the dryness of the wood, etc.

I don't have single wall and can't say how a surface thermometer compares to actual temps of the gases but I do know that comparing flue gases with an IR reading of a double wall is useless. Just about as useless as knowing how hot the fire is by looking at a surface thermometer on a soapstone stove.  

I agree that the true test of any creosote problem is to clean the chimney and if there is a significant build-up, look to evaluate why that is happening.  With the OP, you really can't even do that if you are running hot and the missus is running cool because you are probably burning off any buildup that she creates (if any).  That said, if you are burning wet wood, you could have creosote problems even when you are burning. My suggestion would be to burn as hot as you need to keep your home warm (without melting the stove) and after a few weeks or month, see what you creosote buildup looks like at the top of the chimney.  I check mine every month since I have a newer installation. Next year, probably 2-3 times per winter as it always looks pretty clean.

To answer the OP, my flue gas is reading 700-900 with a hot stove and 400-600 when cruising, both read with air controls at min.  I use a digital flue probe and an IR gun. My soapstone is typically under 300-400 and provides us with far more heat than my old cast iron that ran at 600 on the stove top.


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## pault123 (Mar 11, 2015)

gyrfalcon said:


> I was using a very small Hearthstone Tribute soapstone stove my first three or four years burning, and it's like pulling teeth to get this stove over 400, and wouldn't stay there long when it did get up that high.  It cruised at 350, so spent most of the time around that temp or lower.  I also had plenty of low-temp crappy, smoldering fires from insufficiently dry wood when I was first learning.
> 
> I never had more than a couple of cups of powder creosote from my chimney cleaning, and the cap has so little staining, the chimney sweep is still dubious that I actually do run the thing 24/7 during the winter.
> 
> That said, I have a new insulated stainless steel chimney and superb draft, which is pretty much ideal for clean burning.  You don't say what your chimney is like, which would make some difference, but is almost certainly still fine.  When in doubt, spend the money to clean the chimney after a month or so, and what's in it will tell the story for you.



Chimney setup...


We've got a 316 grade 6" twin wall liner (9 meter tall chimney), and a single wall 5" black stove pipe joining them together. (whats the benefit in a twinfall stove pipe?)

The chimney is of brick construction right to the top, with a 1 meter stack on the roof.


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## pault123 (Mar 11, 2015)

Oldman47 said:


> . If you see steam coming out of the flue you are a bit cool but if you see it show up a few inches away from the cap you are golden. It means it took those few inches of travel to cool the flue gas enough to form tiny water droplets and it was not condensing inside your flue.



Great tip, i'll have a look at this next weekend when i'm burning, I can't get to my chimney pot easily in person, but can view it from the garden which is elevated quite well.


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## pault123 (Mar 11, 2015)

begreen said:


> Our flue runs with a probe thermometer on double-wall pipe typically in the 400-500F range. That is actual the flue gas temp. The chimney is pretty clean with gray powder at the top. This is what works for our setup. It's a straight-up 20 ft chimney with a good portion inside a conditioned space. If this was a single-wall connector going thru a wall thimble into an outside chimney my results might be different. There is much more opportunity for cooling down the flue gases with that setup. Single wall pipe radiates off flue gas heat pretty quickly. Add say 20ft of exterior chimney in cold winter temps and there is likely to be more accumulation.



So if your actual flue gas temp is 400-500F with clean chimney, that would equate to 200-250*F thermo reading on a single wall stove pipe external magnetic reading?


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## pault123 (Mar 11, 2015)

Poindexter said:


> The true test is what your sweepings look like.  If you are getting grey/brown powder out, with a few specks of shiny black in it you're doing pretty darn good.



I'll get it swept once the weather warms up, which could be April/May, that would give me an idea of 4-5 months accumulation.


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## pault123 (Mar 11, 2015)

DougA said:


> I just don't think there is an 'optimum' range for wood stoves unless you break it down into cat/non. cat/ etc., then break it further into sizes.  If you are comparing the creosote buildup vs temps, you then have to take  into account the dryness of the wood, etc.
> 
> I don't have single wall and can't say how a surface thermometer compares to actual temps of the gases but I do know that comparing flue gases with an IR reading of a double wall is useless. Just about as useless as knowing how hot the fire is by looking at a surface thermometer on a soapstone stove.
> 
> ...





I picked up one of these moisture meters, freshly chop the wood and always make sure its less than 20% inside the cut, so hopefully that should be dry enough...







So getting the temps right was the last part of the puzzle to keep it all clean. I do wonder if I should pick up a £30 USB camera to feed up the flue pipe every few months LOL, anyone considered something like this?

http://www.ebay.co.uk/itm/2-5-7-10M...t=LH_DefaultDomain_3&var=&hash=item486cbffa02




Never heard of soapstone before, just had a google, looks an amazing material


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## DougA (Mar 11, 2015)

pault123 said:


> (whats the benefit in a twinfall stove pipe?)


Double wall keeps the flue gases hotter since the double wall acts as insulation.  Hotter flue gases mean better draft and cleaner pipe/chimney since condensation won't occur when the gases are hot.  It's surprising how the temperature decreases as the gases go up the chimney.


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## begreen (Mar 11, 2015)

pault123 said:


> So if your actual flue gas temp is 400-500F with clean chimney, that would equate to 200-250*F thermo reading on a single wall stove pipe external magnetic reading?


Roughly correct. The flue temp is going to also vary with the stage of the burn. Starting up our flue might reach 600-800F for 15-30 minutes. I usually take the stove up a bit hotter with the first morning fire for the first 30 minutes. 400-500F is more of a cruising temp 60 minutes into the burn. Your mileage may vary with the size of the stove, wood charge and draft.


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## DougA (Mar 11, 2015)

I think if you sweep and find very little ash, you will be good without any camera. If you feed it up the flue, you'd probably not see anything until you get close to the top - that's a long way. I doubt that anything at that price will show you much anyway.


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## NHcpa (Mar 11, 2015)

jb6l6gc said:


> I wouldn't trust those magnetic thermometers as far as I can throw em...


Bite your toung! Mine is made in Canada and I rather like it!


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## ToltingColtAcres (Mar 11, 2015)

pault123 said:


> http://www.ebay.co.uk/itm/2-5-7-10M...t=LH_DefaultDomain_3&var=&hash=item486cbffa02



A tube of KY and the Time/Life Home Colonoscopy Series Book and you'll put gastroenterologists out of business with that thing....


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## DougA (Mar 11, 2015)

ToltingColtAcres said:


> A tube of KY and the Time/Life Home Colonoscopy Series Book and you'll put gastroenterologists out of business with that thing....


Yup, got mine on order and opening the new clinic tomorrow.
It takes so little to get the imagination going when you've been without sunshine for 6 months.

I feel the thread lock coming ....


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## Wood Duck (Mar 11, 2015)

How does one fettle a stove?


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## begreen (Mar 11, 2015)

Very carefully.

In this case I think it is being used to mean trim or fiddle with the fire.


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## pault123 (Mar 12, 2015)

yeah fettle is simply tweak/ fine tune lol


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## pault123 (Mar 12, 2015)

DougA said:


> Yup, got mine on order and opening the new clinic tomorrow.
> It takes so little to get the imagination going when you've been without sunshine for 6 months.
> 
> I feel the thread lock coming ....


 Hope not, its been real informative so far, learnt a lot :- )


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## Squirrel (Mar 12, 2015)

Here it is! I've been waiting!!


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## pault123 (Mar 12, 2015)

DougA said:


> I think if you sweep and find very little ash, you will be good without any camera. If you feed it up the flue, you'd probably not see anything until you get close to the top - that's a long way. I doubt that anything at that price will show you much anyway.



I'll stick with the sweep come end of season then :D


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## Creekheat (Mar 12, 2015)

Anyone know a conversion for double wall pipe so you can get Flue gas temps? I have a IR gun and a inferno which very accurate according to my gun.


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## DougA (Mar 12, 2015)

Creekheat said:


> Anyone know a conversion for double wall pipe so you can get Flue gas temps?


There may be one but it would be ballpark at best. For example, I've got 12' of double wall 8" pipe and that provides a lot of air movement between the layers. The double wall I have is not sealed in sections like a piece of chimney pipe is.  So, if you've got a 3' section, there is a lot less flow of air to temper the readings.  

I typically read 200 at the lower section and 100 in the upper section with the flue thermometer at 500-600 but that ratio goes out the window if I have a flue temp of 1000+. That is much more common than most people believe.


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## Grisu (Mar 12, 2015)

Creekheat said:


> Anyone know a conversion for double wall pipe so you can get Flue gas temps? I have a IR gun and a inferno which very accurate according to my gun.



I doubt such a conversion exists. Get an internal flue probe thermometer if you want to know your flue temps.


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