How Hot can I let my flue temps get?

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Hi. Just wondering what you guys consider to be the highest flue temps (digital probe 3' inside flue) reading you will allow? I've always used 315°C or 600°F but I'm wondering if I can safely aim more towards maybe 800° or 900°F?
I'm running double wall to the ceiling, on a basement install).

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bholler

Chimney sweep
Staff member
Jan 14, 2014
28,179
central pa
Hi. Just wondering what you guys consider to be the highest flue temps (digital probe 3' inside flue) reading you will allow? I've always used 315°C or 600°F but I'm wondering if I can safely aim more towards maybe 800° or 900°F?
I'm running double wall to the ceiling, on a basement install).

View attachment 289775 View attachment 289776
1000 f max
 
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Highbeam

Minister of Fire
Dec 28, 2006
19,679
Mt. Rainier Foothills, WA
If that is a thermocouple probe inserted into the double wall pipe so the tip is near the center then yeah, no more than 1000 at that location to protect the chimney. I have an auber thermocouple probe measuring system and I have the alarm set at 950 and rarely see 900. That's ripping hot and you're not exactly being very efficient when chooching that hard. It's really for rapid warm up of a cold stove.

I don't get back down to 600 until the fire is just coals. If you've been staying that low all the time then you should be checking your chimney for creosote!

What stove are you burning? My noncat is happiest in the 700-800 range when I'm trying to run it hard and 650-750 is not unreasonable for medium.
 
Oct 13, 2020
167
Quebec, Canada
I am using double wall stove pipe with a probe type thermometer, I normally let it cruise at 400° - 500°, sometimes it will get up to 600° - 650°, I start getting worried at 750°-800°. New-years eve 2000 I was watching the turn over to year 2000 all over the world, forgot about the stove, it went up to over 1100° and stayed there for about45 minutes, SCARRY, VERY VERY SCARRY !
 
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If that is a thermocouple probe inserted into the double wall pipe so the tip is near the center then yeah, no more than 1000 at that location to protect the chimney. I have an auber thermocouple probe measuring system and I have the alarm set at 950 and rarely see 900. That's ripping hot and you're not exactly being very efficient when chooching that hard. It's really for rapid warm up of a cold stove.

I don't get back down to 600 until the fire is just coals. If you've been staying that low all the time then you should be checking your chimney for creosote!

What stove are you burning? My noncat is happiest in the 700-800 range when I'm trying to run it hard and 650-750 is not unreasonable for medium.
Thanks for the quick replies. Yes, that is a thermocouple with the tip in the middle of the flue. I'm running a Drolet Austral. I have nasty wicked draft, so much so that I installed a key damper in the flue a few years ago, to help me keep things from getting out of control. I haven't had to use it much this year, but I get nervous when the air is completely closed, like today, but the temps still want to keep climbing above 600 F... So it should be ok to let the flue gasses get up to say 750°F (400°C)? Takes about an hour usually before the flames of hell die down a bit and the temps start dropping.
 
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Highbeam

Minister of Fire
Dec 28, 2006
19,679
Mt. Rainier Foothills, WA
Thanks for the quick replies. Yes, that is a thermocouple with the tip in the middle of the flue. I'm running a Drolet Austral. I have nasty wicked draft, so much so that I installed a key damper in the flue a few years ago, to help me keep things from getting out of control. I haven't had to use it much this year, but I get nervous when the air is completely closed, like today, but the temps still want to keep climbing above 600 F... So it should be ok to let the flue gasses get up to say 750°F (400°C)? Takes about an hour usually before the flames of hell die down a bit and the temps start dropping.

Yep, I don’t even turn it down until I hit 850 but my stove responds quickly to adjustments of the draft control so I have no fears of runaway. Let’s put it this way, a clean and properly installed modern class A chimney assembly at your desired 750 is operating within the rated limits.

For reference, here is a labeled mechanical probe meter for stove pipe that gives you the normal operating range.

This is my cat stove 11 hours into a burn cycle or about 50% done with the load. image.jpg
 
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Poindexter

Minister of Fire
Jun 28, 2014
2,562
Fairbanks, Alaska
My through the telescope on center probe routinely measures 600-650dF when I have the stove running on high.

On cold starts I try to limit flue gas temps to 1000 dF. When my gas temps get up around 1400dF on cold starts I hear some rattling in the pipe as it cools back down after my combustor is engaged.
 

Todd

Minister of Fire
Nov 19, 2005
9,576
NW Wisconsin
Some of these flue temps seem high to me. They may be in the safe range but a lot of heat is going up the chimney. I like to see 400-600 flue temps for my setup, seems to give me the best efficiency.
 

Highbeam

Minister of Fire
Dec 28, 2006
19,679
Mt. Rainier Foothills, WA
Middle of the normal range is 650 and a noncat needs pretty hot firebox in order to burn clean, isn't it like 1100 or 1400? Of course, things cool before they get to the probe meter but the point is that you can't run it too cold without risk of high pollution and chimney creosote accumulation. At the top of the scale I agree that there is some loss of efficiency but if you need the heat you need the heat.
 
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I was very happy with my fire this morning. I turned the air down about 90-95% which still left a good solid box of flames & secondaries, and then let it go to see how hot it would get in the flue. It reached just around 350 F and then cruised there for a good hour or so before starting to slowly inch its' way down. Very happy indeed. Thanks for the comments and advice.