140 degree Flue Temp- Is this possible?

[Justkeepinwarm]

New to the forum and I have a question that I can't seem to find the info around the internet.

In an attempt to increase the efficiency as much as possible with my Quadra Fire stove and reading the forums everyone suggests starting with a flue thermometer. I purchased a Condar- 4" Flue Guard thermometer. Mounted it 18" above the stove (back in November) and now understand that my burning temps are in the safe range 400-900 degrees (average is around 500 degrees).

Stove info:
Quadra Fire
Isle Royale
007 1028048
Manufactured Feb 2007

Everything I read said that if I do this Ill be fine. Out of curiosity I wanted to know what the flue gas temp was leaving the flue, so I purchased a "Thermo Pro- Remote Food Probe" (cool little device!) and monitored the temps from the top of the chimney for several nights. I mounted it in the center of the flue about 10" down from the top of the chimney flue using steel rebar as a support.

Here's the Question:
Condar reads 900 degrees / remote sensor (chimney top) reads 190 degrees
Condar reads 500 degrees / remote sensor (chimney top) reads 140 degrees
Should I be concerned about creosote build up, as it is FAR below the 250 degree (safe) threshold?

Here are a few better photos from "Google Photos" of the house lay out and chimney set up in the rear of the house.
https://goo.gl/photos/STvVAEJjBXHab4Fu7

As a side note while I was up there with the ladder I swept the chimney. I did notice heavy buildup (3/16") of creosote/ ash in the 6" metal flue above the stove and not a tremendous amount in the masonry flue. I clean the chimney every April (we burn about 6.5 cord) and I'm sure that I didn't clean the 6" metal flue last year, don't recall the reason??
Is it possible that the draft was effected.
Last night after cleaning, the wood stove ran like a champ! I had already removed the remote sensor and so I don't have more data for last nights burn, I could set it back up again if need be.


Thanks for your help.
Cheers!

 

[begreen]

The Condar is a probe thermometer, correct? Is it mounted onto single-wall stove pipe? If so, the readings may be incorrect. Probe thermometers are calibrated for double-wall stove pipe.

As for the final result, it sounds like you have good dry wood and are burning properly. What did the top interior of the masonry chimney flue look like before cleaning?

 

[Justkeepinwarm]

Single wall pipe is what I have.

My guess is that calibration is probably close enough.
I believe I read something about cruising temps being around 500-700. This seems to be about right with the stove and the way I've always run it. (not saying that I'm doing it correctly but it seems to have always worked well)

1- Typically light the fire then pull out the (starting) air all the way after 10-20 minutes or as soon as the fire really gets going.
2- After about 30-45 minutes, I'll move the control air to about 60% closed for the remainder of the time thats its in use, when I do that the temps stay between 400-900 as I add more wood or as its burns down before adding wood.

Not sure how else to verify temps in the flue, I figured inner flue temps would be more accurate to gauge instead of surface temps alone?

 

[Justkeepinwarm]

The Condar is a probe thermometer, correct? Is it mounted onto single-wall stove pipe? If so, the readings may be incorrect. Probe thermometers are calibrated for double-wall stove pipe.

As for the final result, it sounds like you have good dry wood and are burning properly. What did the top interior of the masonry chimney flue look like before cleaning?

I think your referring to interior stove pipe. If so, thats the pipe that has not been cleaned for 2 years (Iknow, I know, dont comment on this. Not sure what I was thinking last year) This pipe was caked with 3/16" of soot / ash.

 

[pen]

Not sure how else to verify temps in the flue, I figured inner flue temps would be more accurate to gauge instead of surface temps alone?

The probe thermometer is made for a cooler surface (double wall chimney pipe) than what you have with single wall. Using it in your application will make the scale worthless.

For single wall, a good condar (is what I have had the best luck with) surface thermometer will read just as quickly as a probe and will give you correct ranges.

Good luck

 

[Justkeepinwarm]

The probe thermometer is made for a cooler surface (double wall chimney pipe) than what you have with single wall. Using it in your application will make the scale worthless.

For single wall, a good condar (is what I have had the best luck with) surface thermometer will read just as quickly as a probe and will give you correct ranges.

Good luck

Makes sense.
Ill pick up a surface temp.

And here I thought I was outsmarting science!
Is the moral of the story to not overcomplicate the thought process?

 

[begreen]

Note that a stove pipe thermometer surface temps will be much lower than the actual flue gases inside of the pipe. So a 300ºF surface temp will be a 450-600ºF interior flue gas temp. When you purchase the thermometer be sure it is for the single wall stove pipe and not for the stove top. The brightly colored ranges are different on the two.
http://www.condar.com/Stovepipe_Thermometers.html

 

[Justkeepinwarm]

So my original question still stands.

If I've been burning the same way for 3 years now and turning the air down as the fire really flares up. This would mean that in order to keep chimney top temps above the 250 degrees the fire would need to be full throttle. Or is there a difference between my 6" metal pipe and the chimney flue top? Meaning is it fine that the chimney flue top is only 140 degrees? If so what about the buildup that would happen south of the 250 degree safe zone?

 

[begreen]

It sounds like a) you are burning good dry wood and b) the majority of the flue system is staying above the condensation point of creosote. Hard to say whether the top reading is totally accurate. The flue gases cool down the most in the last few feet of exposed chimney.

 

[bholler]

If you are really running at 140 at the top you would see allot of buildup up there of creosote. That is part of the reason we install insulated chimney liners to keep those temps up better.

 

[Justkeepinwarm]

It sounds like a) you are burning good dry wood and b) the majority of the flue system is staying above the condensation point of creosote. Hard to say whether the top reading is totally accurate. The flue gases cool down the most in the last few feet of exposed chimney.

begreen, your response was spot on.
Its possible only the last few feet were below the 250 degree threshold.


After a call to Condar http://www.condar.com/ (their tech support was incredibly helpful) their answer was as follows:
As long as the smoke remains a nice white or lighter, in color, the issue with creosote is minimized. Dark or black smoke would be a different issue.

Enough of the flue remained above 250 degrees allowing minimal creosote buildup in the masonry flue.

I dint think is was a major issue just curious as to the why and how.


Thanks for all the help everyone!