# Differences In Temperatures From Flue To Cap



## turbocruiser (Aug 9, 2011)

I was reading some thoroughly fascinating threads here recently about temperatures inside the inner layers of stove pipe and chimney pipe where people had taken their temperatures at different distances from the flue of the stove.  

In one thread, if I remember right, the interior temp within a foot from the flue was around 650 F, then the temp of the stove pipe about four feet from there was a little lower at around 550 F and presumably as the distance increases the interior temperature decreases at least a little?

So my question is if the interior temperatures of the flue/lowest section of our stovepipe is averaging around 650 F what would I expect the temperature to be towards the topmost section of our chimney cap (20 feet of chimney in this instance)???

I realize it is impossible to precisely pin these temperatures down in this way however I'm more searching to understand theory here and not necessarily trying to perfectly predict temperatures.   Thanks.

Ohh, I didn't specify this but this is 6" ID Double Wall Class A Chimney (Excel) and 6" ID Double Wall Stovepipe (UltraBlack).  Thanks Again.


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## pen (Aug 9, 2011)

With 6 in chimney that is insulated, you will have warmer temps at the cap than someone with a block chimney as yours simply won't absorb and transmit as much heat to the world through it's shell.

The only number I can give you is you'd hope that the temp at the cap is ~200Â°F .  If they flue gases are able to stay that warm, then creosote accumulation should be at a minimum since at warm temperatures the smoke would not have a chance to condense on the chimney walls.

pen


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## turbocruiser (Aug 9, 2011)

pen said:
			
		

> With 6 in chimney that is insulated, you will have warmer temps at the cap than someone with a block chimney as yours simply won't absorb and transmit as much heat to the world through it's shell.
> 
> The only number I can give you is you'd hope that the temp at the cap is ~200Â°F .  If they flue gases are able to stay that warm, then creosote accumulation should be at a minimum since at warm temperatures the smoke would not have a chance to condense on the chimney walls.
> 
> pen



Okay, awesome thanks for that information!  I am going to get an IR thermometer too so I'll shoot that thing towards the top from time to time and report with real numbers but it really helps to have the knowledge that after traveling through twenty feet of chimney its going to lose a lot of heat.  I had imagined having a little loss of heat at the top but this is much more than that.  Thanks Again.


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## Backwoods Savage (Aug 9, 2011)

The correct way to determine that temperature is for you to climb the roof and then stand there with a thermometer to check the temperature. This is best done when the outdoor temperature hovers near 10 degrees with the wind no stronger than 35 mph. Snow should not be falling at the time of this experiment. Please report back next January on the results.


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## turbocruiser (Aug 9, 2011)

Backwoods Savage said:
			
		

> The correct way to determine that temperature is for you to climb the roof and then stand there with a thermometer to check the temperature. This is best done when the outdoor temperature hovers near 10 degrees with the wind no stronger than 35 mph. Snow should not be falling at the time of this experiment. Please report back next January on the results.



Roger That!  I'll actually report on the temps when the weather is cold as well as warm because I'm as interested in how hot it is there in the winter as well as late summer/ early fall when we have nights where it is cool enough to exercise the stove but the attic area is probably still pretty warm from the temps throughout the day.  The second situation is actually the one I'm more "worried with" although I'm actually not worried.  I will report back regarding these temps though.  Thanks Again.


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## Backwoods Savage (Aug 9, 2011)

All joking aside, I too have been somewhat curious on how quickly the temperature will drop while smoke rises. However, I also expect the range of temperatures that different folks would get could be quite great.


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## xman23 (Aug 9, 2011)

My cap must be cold. Every year at cleaning time the pipe has a light coating of dry carbon that brushes off and the cap is a gooee mess. 

Tom


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## turbocruiser (Aug 9, 2011)

Backwoods Savage said:
			
		

> All joking aside, I too have been somewhat curious on how quickly the temperature will drop while smoke rises. However, I also expect the range of temperatures that different folks would get could be quite great.



Gosh, if someone is joking I am basically blissfully unawares!  I seriously will take temp readings throughout the operation of our stove and will report with that data to the fine folks here.  What I'm also wondering about is that all along my stove pipe and my chimney pipe I have MUCH more than the two inches clearance to combustibles BUT right where the chimney pipe exits the chimney chase on our roof the plywood there (under the sheet metal pan placed on top of the chimney chase) is exactly at two inches clearance to combustibles so I was wondering how much cooler the chimney would be towards the top vs. towards the bottom.  Thanks.


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## turbocruiser (Jan 29, 2012)

Okay, this will basically be a pretty funny poke at myself but I was determined to answer this question as scientifically as possible.  I realize that Dennis suggested I should measure my temps at 10 degrees outside and with winds less than 35 MPH however I really didn't want to walk on my shingles when it was colder than about 35 or so just because they're basically too stiff to walk on without crackling sounds coming from them at those temps (yes I actually leaned my ladder up and pushed on the shingles the last time it was 10 degrees without any snow on our roof, and then again at 30 degrees without any snow on our roof, and they still seemed too stiff to walk on without damage). 

So, today we're slowly warming to wonderfully even overcast temps of 50 degrees, there is no wind whatsoever and I decided to take some specific measurements to see how much delta there is in temperatures between the stove to stove pipe to chimney pipe and all the way to the chimney cap too!  

I started the stove up at around 8:30 pm last night, loaded two loads of ash/aspen/elm/oak and burned all the way to 12:30 am then we went to bed with a firebox full of good glowing coals.  This morning at around 7:15am I raked forward all the remaining coals and completely restarted a pretty full firebox of the same stuff.  I added another load at around 11:15 and at that time had a heap of good glowing coals and several splits starting with super big secondaries end to end.  Between 11:15 and 12:00 noon I setup my several ladders and prepared to take measurements with my Fluke IR Laser Thermometer.  I also adjusted for proper emissivity settings between stove, stove-pipe and chimney pipe.  Here are my various measurements (with Regency CS1200 Stove, ICC UltraBlack Double Wall Stove Pipe and ICC Double Wall Excel Chimney Pipe):

Outside Air Temp: Rising From 25 F to 50 F from 7:00 am to 12:00 noon while fire was restarting
Inside Air Temp: Rising From 72 F to 80 F throughout the whole house with furnace heat off but furnace circulation on.     
Firebox Front Face Discharge Area Above Door:  676 F
Actual Stove Top: 686 F
Floating Stove Top: 325 F
Chimney Connector: 600 F
Bottom Of Outside Diameter Of Stove Pipe: 400F
Top of Outside Diameter Of Stove Pipe (after 4 ft straight, 30 deg offset, 1 ft straight, then another 30 deg offset): 186 F
Bottom Of Outside Diameter Of Chimney Pipe (inside the square chimney support): 125 F
Top Of Outside Diameter Of Chimney Pipe (20 foot straight chimney pipe): 76 F
Underside Of The Top To The Chimney Cap: 126 F

So roughly from the outside of the chimney connector to the underside of the top to the chimney cap the delta was 474 degrees and it was 524 degrees from the outside of the chimney connector to the outside of the top of our chimney.  This gives me great information and also tells me that I should probably try to set the stove higher at around 800 F to get the gasses coming out of the top of our chimney to the 200 F mark that pen recommended.  Anyways, I realize that part of the offered advice here was just in jest but just to put some proper data to my sometimes stupid questions, I thought that I'd follow up as promised in the hope it helps others; it definitely did help me understand a bit better how hot things would get.  Thanks.


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## Jack768 (Jan 29, 2012)

Interesting.  But burning the stove at 800 all the time could be quite difficult and you're close to an overfire at that point.


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## Hass (Jan 29, 2012)

When I started reading this... I was thinking I could put a wireless thermometer up at the top of the cap by tying it off to the chimney cap and hanging it inside the chimney a foot or so. But then I realized if it falls off the cable in to the fire, that would be bad -.-

Perhaps something with a metal probe on a cable that can hang in would be best...
Hum... I have some searching to do.

I wonder this, because when the stove is on low the flue gas 18" off the stove are about 200-210F. If it drops down 20-30 degrees at the top, that would be creosote forming day after day.


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## turbocruiser (Jan 29, 2012)

turbocruiser said:
			
		

> Okay, this will basically be a pretty funny poke at myself but I was determined to answer this question as scientifically as possible.  I realize that Dennis suggested I should measure my temps at 10 degrees outside and with winds less than 35 MPH however I really didn't want to walk on my shingles when it was colder than about 35 or so just because they're basically too stiff to walk on without crackling sounds coming from them at those temps (yes I actually leaned my ladder up and pushed on the shingles the last time it was 10 degrees without any snow on our roof, and then again at 30 degrees without any snow on our roof, and they still seemed too stiff to walk on without damage).
> 
> So, today we're slowly warming to wonderfully even overcast temps of 50 degrees, there is no wind whatsoever and I decided to take some specific measurements to see how much delta there is in temperatures between the stove to stove pipe to chimney pipe and all the way to the chimney cap too!
> 
> ...







			
				LIJack said:
			
		

> Interesting.  But burning the stove at 800 all the time could be quite difficult and you're close to an overfire at that point.





Actually, with the air control as low as ~10 % open the stove seems to prefer to cruise at 750 to 850 and I'm always running around measuring all the surfaces to make sure it isn't hitting 900 anywhere!  At 850 I switch the blower from low to high and it settles down soon enough at around 750 again.  Then at 650 I switch the blower from high to low.  

I called and asked Regency about this and they told me that even these extreme temps are alright.  

Keep in mind I'm shooting straight towards the firebox between the side shields and top shields for these temps; even at 850 firebox temp the floating top is only in the 500 to 550 F range.  To get the floating temp in the 800 F range the firebox temp would probably be pushing 1000F!  Yikes!

What I've loosely learned so far is that if I completely close the air control with a full firebox I will quickly reach a really nervous 950 and probably above.  The secret to cruising at 700 seems to be the setting of ~25% air.  The secret to cruising at 850 is ~10% and some adjusting of the blower to prevent temps above 900.

I should end stating I'm no expert; these are just my findings so far.  Anyone's thoughts are always welcomed.  Thanks.


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## Swedishchef (Jan 29, 2012)

Wow. You did one pile of work for that research.
It gives me an idea what temps mine are at...but I kinda have a bit of a problem setting a stove at around 800 most of the time. There must be a fine line in your primary air adjustment between that cruising temp and going nuclear.

I was told that my probe thermo temp should NOT be over 500F: otherwise you're losing too much heat up the chimney and the stove becomes much less efficient. I am uncertain how much truth there is to this concept...

Thanks for the info!

Andrew


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## greythorn3 (Jan 30, 2012)

Hass said:
			
		

> I wonder this, because when the stove is on low the flue gas 18" off the stove are about 200-210F. If it drops down 20-30 degrees at the top, that would be creosote forming day after day.



and thats what im not liking about the cat stoves at this point. try getting any heat out the top when its -25f and your interior black pipe 18" off the stove is low 200f i personally think a cat stove seems to be a recipe for disaster in cold cold climates like alaska.


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## Huntindog1 (Jan 30, 2012)

As a related note, I have had at times stove temps up and secondaries going  but have smoke coming out the flue , but it looked like a light smoke like its was maybe more a steam and smoke mixture.

I have a masonry flue 25 foot tall 7"x11" and I figured that by the time it got to the top it cooled enough to show up more as smoke.

Now you guys with 6" insulated all the way , I suspect your flue gas velocity is faster and the insulated flue keeps it hotter , being hotter all the way up there accounts for the faster velocity and the faster it goes less time for it to cool.

So by the time it gets to coming out the top of the flue its still pretty hot so it doesnt show a visible smoke like a cooled flue gas would look.

Plus if there is less residency time in the flue and the flue stays hot the entire length of the pipe instead of cooling then there is less chance for creosote accumulation.


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## begreen (Jan 30, 2012)

> Here are my various measurements (with Regency CS1200 Stove, ICC UltraBlack Double Wall Stove Pipe and ICC Double Wall Excel Chimney Pipe)



Not unusual at all for surface temps on double-wall pipe. Surface readings are not a good way to measure flue gas temps with double-wall. From the data turbocruiser just posted it sounds like everything is running ok. Draft might be a little strong or maybe the splits could be a little fatter. 

Turbocruiser, can you take a picture and post it of your normal reload? Also, can you add your stove make/model to your signature?


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