# Double Wall Flue Pipe, Burn Temps & Thermometers



## soupy1957 (Feb 11, 2010)

Yesterday, my wife saw that the needle on our stove thermometer, was 700ºF + and said to me, "Hey, according to the charting on this Thermometer, we're burning in the "Danger Zone."  I didn't know what to tell her, and said "I believe that this Thermometer is designed to read Flue temps, and since we have a double-walled Flue, it wouldn't read accurately, so I put it on the front flange of the stove, just to get an idea of the heat in the box; but that's not representative of what the heat is, in the Flue."

First, the double-wall Flue pipe is only double-walled as far as the ceiling baffle, correct?  Beyond that, it's single wall, right?

Second, the temps that the thermometer is reading on the face flange of the stove is the fire box temp, and not the Flue temp, yes?

Third, the "Danger Zone" shown on the thermometer is for Flue temp safety, right?

Fourth, (and I think I asked this before) there is nothing bad about running the stove consistantly up around 650ºF to 750ºF, correct?  (If anything, it's a great creosote destroyer).

-Soupy1957

P.S.: By the way........here's the thermometer that we bought: (I think this link is to an older version, because the right side of the gauge reads "Danger Zone" on ours).

http://www.amazon.com/Imperial-BM01...8-3624519?ie=UTF8&s=hi&qid=1265892724&sr=8-11


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## Jags (Feb 11, 2010)

soupy1957 said:
			
		

> Yesterday, my wife saw that the needle on our stove thermometer, was 700ºF + and said to me, "Hey, according to the charting on this Thermometer, we're burning in the "Danger Zone."  I didn't know what to tell her, and said "I believe that this Thermometer is designed to read Flue temps, and since we have a double-walled Flue, it wouldn't read accurately, so I put it on the front flange of the stove, just to get an idea of the heat in the box; but that's not representative of what the heat is, in the Flue."
> 
> First, the double-wall Flue pipe is only double-walled as far as the ceiling baffle, correct?  Beyond that, it's single wall, right?
> 
> ...



First - double wall "Can" be from stove to sun light.  Depends on your install.
Second - if the thermo is on the stove its stove temp
Third - That thermo was designed to hang on single wall stove pipe so disregard the "zones" on the thermo.
Fourth - that depends on your stove manual and MFG. recommendations.  With my stove I hit 700f daily (stove top).

To add - if you do in fact have double wall pipe from stove to sunlight - your in need of a probe thermo to get accurate stack temps.


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## Snowy Rivers (Feb 11, 2010)

Almost any proper install is going to have an insulated pipe running all the way from the cieling jacket up through the overhead crawl space to daylight.

Every jurisdiction is or can be slightly different.

A single wall pipe close to the stove can see 700F easily.

With temps like these you wont be having creosote issues either.

Cold lazy fires are more of an issue than a hot one as long as the stack is done correctly.

If you really want to know what the flu gas temps are, install a probe type gauge into the stack about 2 feet above the stove.


Snowy


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## begreen (Feb 11, 2010)

700 °F on a stove top may not be a big deal, depending on the stove. But the same temperature on a double-wall pipe is way too hot if the thermometer is accurate. Actually it's pretty hot for single wall, indicating a flue gas temp of around 1000 °F. That's a lot of waste heat to send outdoors and pretty stressful for the pipe if sustained for hours.


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## firefighterjake (Feb 11, 2010)

soupy1957 said:
			
		

> Yesterday, my wife saw that the needle on our stove thermometer, was 700ºF + and said to me, "Hey, according to the charting on this Thermometer, we're burning in the "Danger Zone."  I didn't know what to tell her, and said "I believe that this Thermometer is designed to read Flue temps, and since we have a double-walled Flue, it wouldn't read accurately, so I put it on the front flange of the stove, just to get an idea of the heat in the box; but that's not representative of what the heat is, in the Flue." _*You would be correct . . . most stove thermometers are designed to give the temp from a single wall stovepipe and as such the "danger, too hot", "danger, you're a creosote factory" and "Ah, that's the spot" readings are not right when these thermometers are used for stove top temps . . . and you are correct . . . this thermometer would not have worked with double wall pipe.*_
> 
> First, the double-wall Flue pipe is only double-walled as far as the ceiling baffle, correct?  Beyond that, it's single wall, right? _*Depends . . . as mentioned already*_.
> 
> ...


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## soupy1957 (Feb 11, 2010)

Some great stuff here guys............thanks

Talked to my Installer moments ago, and asked if it was "double wall" Flue, all the way to the sky, and he said yes, it's galvanized double wall in the attic and out the roof.......the telescoping double wall Flue from the stove to the ceiling is double wall as well, but it's "black" (whatever the material is).


 -Soupy1957


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## Jags (Feb 11, 2010)

soupy1957 said:
			
		

> Some great stuff here guys............thanks
> 
> Talked to my Installer moments ago, and asked if it was "double wall" Flue, all the way to the sky, and he said yes, it's galvanized double wall in the attic and out the roof.......the telescoping double wall Flue from the stove to the ceiling is double wall as well, but it's "black" (whatever the material is).
> 
> ...



Most likely it is stainless.  You will need a probe thermo for that double wall to get accurate internal stack readings.  Easy to install and a great learning tool.


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## Pagey (Feb 11, 2010)

Soupy,

You'll find there are really "two types" of double wall (in general) when dealing with a solid fuel appliance.  There is double wall STOVE/CONNECTOR pipe, which is the black pipe that goes from the stove to the ceiling support box.  Then there is double wall CHIMNEY pipe, which is the Class A UL 103HT type pipe (usually stainless, but there is also galvanized, I believe).  

You can run the black stove pipe (single all OR double wall) to the support box, but anything past that has to be the double wall Class A.

If you are getting an external temp of 700F on double wall stove pipe, I can only imagine what the inside flue gas temp is.  Keep in mind that Class A 103HT is rated for 2,100F max and 1,000F continuous.

My steel Endeavor will spike to 700F on the STOVE TOP with a fresh load, but I've only seen it past that a couple of times, and those were last year when I had a poor door seal and some displaced fire bricks in the baffle.  Now the stove settles in around 650F at the peak and settles down from there.  I've never measured by external double wall stove pipe, but I do know that even when the stove is cruising at 650F I can very briefly place my hand on it.  That would lead me to believe it's well below 700F.


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## soupy1957 (Feb 11, 2010)

which temp is more critical to monitor, I guess is the question...........my stove temp or my Flue Temp?

Is there a common understanding (in chart form, if I'm really lucky) that states the temp comparisons?  For example.......if some stove is running at 700ºF, the Flue will be XXXºF?  Are there any comparisons like that out there, say from 450ºF to 1000ºF???????

-Soupy1957


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## Jags (Feb 11, 2010)

soupy1957 said:
			
		

> which temp is more critical to monitor, I guess is the question...........my stove temp or my Flue Temp?
> 
> Is there a common understanding (in chart form, if I'm really lucky) that states the temp comparisons?  For example.......if some stove is running at 700ºF, the Flue will be XXXºF?  Are there any comparisons like that out there, say from 450ºF to 1000ºF???????
> 
> -Soupy1957



Nope!  Each install will have its own characteristics.
I would say that stove top is MORE important, but both ARE important.  Is the fuel gauge or the engine temp gauge more important in your car?

Both - they both will give you valuable information.


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## pen (Feb 11, 2010)

soupy1957 said:
			
		

> which temp is more critical to monitor, I guess is the question...........my stove temp or my Flue Temp?
> 
> Is there a common understanding (in chart form, if I'm really lucky) that states the temp comparisons?  For example.......if some stove is running at 700ºF, the Flue will be XXXºF?  Are there any comparisons like that out there, say from 450ºF to 1000ºF???????
> 
> -Soupy1957



That will depend on where you are in the burn cycle, amount of primary air used, and lots of variables in general.  So no, there is no exact rule.

After the investigations I've done recently regarding the accuracy of flue probe thermometers, I will say that IMO that if I were to have only 1 thermometer it would be placed on the top center of my stove top.  For my circumstance, I aim to keep it 550-700 for a good burn.

A magnetic surface thermometer will do you no good on your flue since you have double wall pipe.

If you decide to get a probe thermometer, I suggest you place it AT LEAST 2 feet above your stove top in the pipe.  My probe thermometer was reading extremely high at 18 inches above the flue collar (in comparison to it's stated "normal operation" zone).  I found that I only was able to get reasonable readings when placed about 28 inches above my stove.

pen


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## Highbeam (Feb 11, 2010)

Stove top is always the most important. The point is to operate your system at high enough temperatures to prevent creosote. You will have short bursts of hot or cold flue temps but if you can maintain good and warm temperatures on the stove then the vast majority of flue gasses will not be creosote forming. The stove top temps will tell you how much heat you are getting into the living space, it will tell you if your burn is efficient, and will tell you if you are overheating and ruining the very expensive stove. 

We've had plenty of folks on this site with overheated and warped, cracked, or busted stoves due to overheating them but I have never heard of someone damaging a metal flue system unless they have a chimney fire.


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## soupy1957 (Feb 11, 2010)

Here's something I can contribute to this thought pattern.............when the install was going on, and the thermometer was handed to me, I asked him if I should put it on the top of the unit, and he said, (after getting a fire going to test the unit), "Well, put your hand over the top of the stove." (I did) "not all that warm," I said.  He said, "now put your hand over the angled flange above the door." "Hey," I said, "that's much hotter."   "Put your thermometer on that flange."

There it sat for the first three weeks.   Then (as per another thread I started in here), I tried moving it (when it was cool), to the center of the overhanging flange, and the temp was much hotter!  I attributed that to being over the glass, and more over the center of the fire (in essence). It was reading at LEAST 100ºF hotter than being on the right side of the overhanging flange.

So when you say, put your thermometer on the "top" of the stove, I'm going to assume for the time being, that the flange location is the better reading point.

As for the probe for the Flue, I recall a thread by someone in here who said that when the temp got up there, the probe didn't stay horizontal to the floor. Obviously the heat affected its mounting.  I'm not too keen on drilling a hole in my Flue (mechanically inclined, but don't want to screw it up), for it.  I realize that it's the best way to get an accurate read for a double-wall Flue pipe, however.

(By the way.........I"m STILL trying to teach the wife how to get a GOOD fire going.........she struggles.....lol)

-Soupy1957


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## Pagey (Feb 11, 2010)

Well, my Endeavor is a step top model, so I place mine in the middle of the bottom/lower plate.  I would say the "flange/lip" area of yours would be the rough equivalent.


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## Jags (Feb 11, 2010)

soupy1957 said:
			
		

> As for the probe for the Flue, I recall a thread by someone in here who said that when the temp got up there, the probe didn't stay horizontal to the floor. Obviously the heat affected its mounting.



On double wall pipe, I'm not sure how that could even happen.  You have an inner wall, insulation, then an outer wall.  Think of it like setting a pipe on saw horses.  If it was single wall, thats a whole nuther thing.


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## Highbeam (Feb 11, 2010)

No Jags, he's right. When you drill the double wall pipe to install the probe you are probably going to do it when the pipe is cool. At least I did. Then when you heat the flue with your fire you will find that the two layers of steel supporting the probe meter expand at different rates so that your probe meter face which was perfectly vertical in the cold flue now points up towards the ceiling from the original position. It's not extreme but it is very noticeable and not something that I expected. If I could do it again I would drill the pipe when it's warm to lessen the apparent tippage. This wouldn't happen with single wall.

Double wall connector pipe doesn't have insulation. You're thinking of class A.


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## Troutchaser (Feb 11, 2010)

Soupy
I am not mechanically inclined and I installed a probe into my double wall.  If you can use a drill, you can do it.  I drilled both holes 1/8", then redrilled the outer hole to 1/4".  The instructions will tell you.
Insert probe through both holes and admire your handy work.
Took 3 minutes after gathering drill and bits.

I can't imagine not having it now.


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## pen (Feb 11, 2010)

Point is, to get into a habit or routine with your stove.  I have a probe thermometer on the pipe 28 inches up, a rutland on the hottest spot of my stove top and a rutland in the front 1/3 of my stove's side where the side is not protected by firebrick or secondary air.

Here's just a few examples of how my thermometers "tell me" what is going on.


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## Jags (Feb 11, 2010)

Highbeam said:
			
		

> No Jags, he's right. When you drill the double wall pipe to install the probe you are probably going to do it when the pipe is cool. At least I did. Then when you heat the flue with your fire you will find that the two layers of steel supporting the probe meter expand at different rates so that your probe meter face which was perfectly vertical in the cold flue now points up towards the ceiling from the original position. It's not extreme but it is very noticeable and not something that I expected. If I could do it again I would drill the pipe when it's warm to lessen the apparent tippage. This wouldn't happen with single wall.
> 
> Double wall connector pipe doesn't have insulation. You're thinking of class A.



I could see that as a possibility I guess.  I have never seen it happen (and this is the first time I have heard of it).  The insulation (or not, cuz your right, I was thinking of class A) shouldn't really play a roll in the stability of the two points contacting the probe (inner and outer walls).  Now if you gots one of them hoochie dancing double wall pipes, all bets are off. ;-)


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## firefighterjake (Feb 11, 2010)

I personally like both of my thermometers . . . the stove top thermometer helps me determine when to start cutting back the air and it lets me know when I'm approaching over fire temps . . . and my flue thermometer helps me burn hot enough to prevent creosote build up and cool enough to prevent a chimney fire. My vote is to get both . . . but if money was tight I would go with the stove top temp first and foremost . . . as Highbeam mentioned if you're running the stove hot enough for secondary burning you're most likely running the flue temps hot enough to prevent creosote formation and most likely have the air kicked back so you're not running it so hot as to risk a chimney fire.


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## soupy1957 (Feb 11, 2010)

See now,..........there it is again "over fire temps"..............define that..........over fire temps in the Flue or the Fire Box?
Isn't it basically true that builders of wood stoves, (reputable ones, who make quality stoves), know the potential heat generation of a Fire Box full of wood, and build it to be able to handle those temps, without melting, popping the weld joints, folding the legs, etc...?????

-Soupy1957


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## Pagey (Feb 11, 2010)

"Overfire" will depend on your stove and your manufacturer.  My Endeavor manual, for example, says that "generally, temps exceeding 800F" are considered over firing the stove.  Some soapstone makers specify 600F or 650F, for example.  I'm not sure about cast.

I'm sure the manufacturers take all sorts of variables into account when designing and testing a particular stove, but if you as the user walk away from a fully loaded stove with the air wide open and good dry wood, then no amount of "manufacturer's consideration" will help, I feel.


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## Jags (Feb 11, 2010)

soupy1957 said:
			
		

> See now,..........there it is again "over fire temps"..............define that..........over fire temps in the Flue or the Fire Box?
> Isn't it basically true that builders of wood stoves, (reputable ones, who make quality stoves), know the potential heat generation of a Fire Box full of wood, and build it to be able to handle those temps, without melting, popping the weld joints, folding the legs, etc...?????
> 
> -Soupy1957



If you go out to your jeep - start it up - and slam the gas pedal to the floor while in Neutral - whats gonna happen?  Melting, popping and broken stuff.  There are operational limits on darn near every piece of equipment short of an anvil.  A stove is no different. (and I know people who could screw up an anvil. :lol: )


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## Highbeam (Feb 11, 2010)

soupy1957 said:
			
		

> See now,..........there it is again "over fire temps"..............define that..........over fire temps in the Flue or the Fire Box?



There are two overfire temps, the flue at 1000 continuous/2100, and the stove at whatever the manufacturer tells you. My stove overfires at 600 my old Lopi overfired at 800 OR when something glows red. You have to figure it out for your own stove.

It is wrong to assume that the manufacturer designed the stove to handle any temperature that the fuel load can produce.


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## soupy1957 (Feb 11, 2010)

".......screw up an anvil"...........lolololol

If I go out to my Jeep and put it in Neutral, and run the gas peddle to the floor and leave it there for a loooooooonnnnnngggg time, it might break something.........probably a push rod, ..........I get the point.  Thing is.........stoves are in a constant state of heating up/cooling down, heating up/cooling down......

-Soupy1957


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## firefighterjake (Feb 12, 2010)

Jags said:
			
		

> soupy1957 said:
> 
> 
> 
> ...



Kind of like what happened to this guy, huh?

http://www.bangordailynews.com/detail/136598.html

--

Man charged after truck, garage catch fire
Officials: Squealing tires started blaze 

By Heather Steeves
BDN Staff 


SOUTH THOMASTON, Maine — A man who was squealing his tires by pressing his feet simultaneously on the brake and gas pedals until his truck caught fire also caused a building to go up in flames, according to fire officials.

Lance McLain, 43, of Owls Head, who suffered minor injuries in the Monday incident, has been charged with operating a motor vehicle while under the influence of intoxicants and violating his bail conditions. He is being held in Knox County Jail on $500 cash bail.

The district attorney’s office is reviewing the State Fire Marshal Office files on the case and deciding whether further charges are warranted.

“It’s classified as power braking,” South Thomaston Fire Chief Bryan Calderwood said about McLain’s alleged activity. “He was doing that and he was doing it within five feet of Island Auto; that [building] is a total loss.”

The vehicle caught fire, which spread to the garage, according to authorities.

“His excuse was that he was having problems with his vehicle,” said Detective Sgt. Reggie Walker with the Knox County Sheriff’s Department. “He revved his engine so much that the engine compartment caught fire, we suspect.”

Walker said McLain, who used to be a mechanic at Island Auto, got out of his truck and went to a nearby store after revving the engine and squealing his tires. By the time he returned, his truck was on fire and flames had spread to the garage.

Approximately 60 firefighters manning 10 firetrucks were able to save the attached automotive paint shop, two vehicles in the building and a few local businesses, according to Calderwood.

The owner of the garage, Matt Gray of Spruce Head, said his insurance agents are checking out the paint shop and the vehicles, which all were damaged.

Gray could not estimate the cost associated with the fire damage.

The firefighters fought flames from 7 until 11 p.m. and used more than 13,000 gallons of water.

“It was an old building; it went up pretty quick,” Walker said. “There were several small explosions in the fire” caused by chemicals stored in the garage.

McLain had minor injuries, including smoke inhalation, and was taken to Penobscot Bay Medical Center.

South Thomaston, Rockland, Thomaston, Saint George and Owls Head fire departments went to the fire, as did South Thomaston and Saint George ambulances, in addition to Maine State Police, the county sheriff’s office and the State Fire Marshal’s Office.

“Considering the weather — it wasn’t freezing — all my guys did an excellent job saving the paint shop and we did conserve,” Calderwood said. “We did a quick stop of the fire.”

Gray said he is not sure if he will rebuild the garage.

“We’re waiting to see what they charge him with,” Gray said, referring to McLain. “If he has insurance, I want to see what I can get out of him.”

Gray rented the garage to a man who he said is now out of work. Gray’s store, The Sea Store at 20 Island Road in South Thomaston, is taking donations for the now unemployed mechanic.

Lance McLain was charged with assault, refusing to submit to arrest or detention, disorderly conduct and driving to endanger in April 2009. He also was charged in 1991 with unnecessary noise with a motor vehicle and several other minor crimes


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