Use of a flue thermometer

[Jay H]

I just installed a flue thermometer (a Condar 3-19 which is on a double wall flue/chimney) on a Quadrafire 3100i.

Now I know the instructions say to close the primary air valve after about 5 minutes after starting a fire to prevent overburning. Now that I have my flue thermometer, I can simply use that as when to close/open the air right? 5 minutes seems kind of arbitrary to me and I think I could use the flue gases as a temperature gauge as to how hot the firebox actually is. The thermometer says to run the flue gas over 400deg to prevent creosote buildup.

Jay

 

[jtcedinburgh]

Good question. I don't know whether it's something to do with my own stove, but after 5 minutes, even with all the valves open and the door slightly ajar, I'm lucky to have even reached 100F on the flue thermometer. I have to 'actively' keep on top of the fire until it passes approximately 200-220F (flue temps) before I can start to close down the valves. So perhaps the 5 minutes thing is a bit pie-in-the-sky...

 

[jtcedinburgh]

On another note, you say that:

The thermometer says to run the flue gas over 400deg to prevent creosote buildup

...yet I find it quite difficult to maintain temps that high, as far as my flue-temp readings are concerned, unless I open up the secondary air (and/or give it a sustained blast of primary air) - If I really load the stove up, I can get it to 'idle' at around 375F flue-temps, but no higher.

 

[BrotherBart]

On another note, you say that:

The thermometer says to run the flue gas over 400deg to prevent creosote buildup

...yet I find it quite difficult to maintain temps that high, as far as my flue-temp readings are concerned, unless I open up the secondary air (and/or give it a sustained blast of primary air) - If I really load the stove up, I can get it to 'idle' at around 375F flue-temps, but no higher.

If you are using a pipe surface thermometer then it is apples and oranges. I have probe thermos on my stoves. Surface thermos register around half the internal flue gas temps. I maintain my burns where the internal probe indicates four hundred or a little over and the stacks are emitting just a nice clear heat flume. That would be around 250 to 300 on the surface mount jobbies.

With either one, of course, during startup you are going to get significantly higher flue temps but they settle in as the burn is established.

BTW: For you folks with single wall pipe, the eight buck stainless steel 700 degree Charm-Glo barbeque probe thermo from Home Depot is doing exactly the same job in my single wall pipes as my megabuck Condar probe. I just drilled out one of the pipe joint screw holes in each pipe and replaced them with the barbeque probes. Stainless steel, including the attaching nut, easy to read and a glass covered dial. I love the darn things.

 

[Jay H]

The 3-19 is a probe thermometer and I drilled out the 1/4" hole through the double wall flue.

After the initial burn when I pile a bunch of newspaper clippings and cardboard when the temps go 400deg+ the burn cools down til I have about 3 decent sized logs going good and the temps get as high as 550, but yeah, when the fire settles and idleling it starts to go down towards 250 or so... At least this is what I noticed last night when I had my first fire with the flue probe in.

Jay

 

[begreen]

Hi Jay, welcome aboard. What brand is 3-19? What kind of stove are you running?

I don't have a flue thermometer yet, so I'm curious as to what is working best for folks. I've been waiting to see how BB's turned out. Good to hear it's hanging in there. But my stove typically runs much hotter on the surface thermometer. Stovetop readings how it runs at 5-600 for an hour or two then will run between 4-500 for a few hours.

Edit - whoopsee. missed the beginning of the thread mentioned it was a Condor on a Quad.

 

[jtcedinburgh]

So, I take it that I ought to be taking my pipe-mounted thermometer's readings with a pinch of salt?

If so, heaven knows what the *true* flue temperature must have been when I hit an indicated 550F on the flue therm...

 

[BrotherBart]

So, I take it that I ought to be taking my pipe-mounted thermometer's readings with a pinch of salt?

If so, heaven knows what the *true* flue temperature must have been when I hit an indicated 550F on the flue therm...

Nah. No salt needed. Also if you have the thermo within twelve inches of so of the stove top it is going to register a little high.

 

[jtcedinburgh]

BB - I was more concerned about it reading low - e.g. it reads 450F when it's really 700F (say) and the chimney liner is slowly melting away (I exaggerate of course )

 

[Jay H]

The 3-19 is the model name for the Condar 3-19...((broken link removed to http://www.condar.com/meters.html), scroll down). AFAIK, the 3-19 is simply the same as the 3-39 without the fancy color scheme.....

P.S. the mounting instructions on the Condar says 18" above the stovetop...

Jay

 

[BrotherBart]

BB - I was more concerned about it reading low - e.g. it reads 450F when it's really 700F (say) and the chimney liner is slowly melting away (I exaggerate of course )

It is fairly safe to say that if the surface thermo is reading 450F then you are kicking around 900F internal flue temp. That is about the top end of where you want to go. Over 900F I would say you are in over firing territory. Personally I would keep the surface temp reading between 250 and 400. Of course I think all surface mount thermometers lie so if you come across a reasonably priced probe, grab it.

 

[begreen]

BB, this must vary from stove to stove. Most folks are reporting Jotuls and VC and Quad cast iron stoves run hotter than that on the stovetop. It would be hard to keep my stove burning in the 250-400 range without adding green wood. Does your 3CB stay at these low temps? Ours ran at similar higher temps.

Edit - The Jotul manual says the most efficient burn for the F400 is between 400 and 600F measured on the stovetop.

 

[BrotherBart]

BB, this must vary from stove to stove. Most folks are reporting Jotuls and VC and Quad cast iron stoves run hotter than that on the stovetop. It would be hard to keep my stove burning in the 250-400 range without adding green wood. Does your 3CB stay at these low temps? Ours ran at similar higher temps.

Edit - The Jotul manual says the most efficient burn for the F400 is between 400 and 600F measured on the stovetop.

I was talking about the surface temp of the pipe BG. My Jotuls at a stove top temp of 500 run a flue temp pretty close to the same on the probe. On the surface of the pipe a thermo registers between 250 and three hundred at that stove top temp.

 

[begreen]

Ah thanks for the clarification. I am laying off coffee for awhile and my mind is slow to get into gear.

 

[jtcedinburgh]

OK, I'll look into getting a flue-probe. My surface therm is a Condar 3-16. Is the 3-39, (link (broken link removed to http://www.condar.com/meters.html)) probe thermometer worth the money?

Also, I assume they need to be removed when the flue is swept?

 

[Jay H]

Yes, the instruction manuals say to remove the probe when you sweep the chimney. Since it is simply held onto the stovepipe via a magnet, this is easy to do.

As far as the cost between the 3-39 and the 3-19 which I have, I bought mine for $27 shipped direct from Condar... If the only difference between the two is the 3-39 having the colors, the $2.35 price difference to me is not worth it. I can see the white pointer against my black stove and I can eyeball it whether it is around 200deg or 400deg. And if I really feel like it, I can always paint the dial a bit with engine paint that I have leftover. I am happy with the 3-19 and don't feel like I would of benefited by spending any more for the 3-39. At least that's my opinion... YMMV, of course.

Jay

 

[Mike]

What difference in readings would there be between the temps on a stove top thermometer on an insert and and flue mount or flue probe thermometer?

 

[pistonslap]

I have a condar chimguard thermometer. My flue comes out the back rather than the top so it may throw the readings off a bit. I take my readings as a ballpark figure because sometimes it says that my temp is too low and creating creasote, but I open my door and the coals are orange and there is flame on the logs. Also, I'll go outside and look and either there is no smoke or the smoke is clear. I think I need to break down and buy a probe.

 

[begreen]

I prefer the cleaner dial look too. Thanks for the info Jay, I didn't know one could by them direct from Condor. I'm going for the 3-19.

 

[Jay H]

No Problem. In fact, Condar was very nice to work with. I originally bought a basic Condar surfacemount thermometer from a local fireplace store. The salesman at the fireplace kept insisting that the surface thermometer would work on a doublewall flue even though I thought that odd since I know a doublewall flue is going to insulate the flue gases alot. After more insisting and a confused look to the salesman face, I bought it and went back to work. After work, I emailed Condar who confirmed what I thought all along. They offered to refund the price of the surface mount thermometer if I simply returned it to them and bought the 3-19. Since I just bought it and I never opened the package, I told them I'd simply return it to the store I bought it from and I went and bought the 3-19 right from them. 2 days later, I got the package on my door and instlalled it not long after.

I do like the cleaner dial myself, as the face of the dial is black, just like my stovepipe.

Jay

 

[Jags]

I prefer the cleaner dial look too. Thanks for the info Jay, I didn't know one could by them direct from Condor. I'm going for the 3-19.

BeGreen - I have had the 3-19 for about 5 years. It is a great tool for monitoring your stove. I keep the flue temps in the 450-850 degree range and it makes for a happy stove.

 

[BrotherBart]

I prefer the cleaner dial look too. Thanks for the info Jay, I didn't know one could by them direct from Condor. I'm going for the 3-19.

BeGreen - I have had the 3-19 for about 5 years. It is a great tool for monitoring your stove. I keep the flue temps in the 450-850 degree range and it makes for a happy stove.

Yep. As an old turbine engine aircraft maintenance chief I can tell you that exhaust gas temps on pretty much any combustion device will tell you more about what is going on than anything. It will tell when the intake air is set wrong, the wood is crap and just about anything else you need to know.

I have a Candor remote probe with analog display that works up to 2,500 degrees. It is a tad of overkill for these stoves so it is resting these days. The BBQ thermos are telling it all for EGT on these stoves.

 

[Jags]

Hee, hee, hee - remote probe :bug: