What temps should I expect in double wall flue pipe....

G'day all. I love this time of year when everyone starts to kick back into burning their stoves... love all the questions and discussions. Anyway, when I swapped out my old stove for the Drolet Austral I also decided to switch to telescoping double wall flue pipe for efficiency and ease of cleaning and whatnot. Although I've been running my stove on and off now since October, I just got around to putting a thermocouple (with a digital readout) into the stack, and now I realize that I'm not sure what sort of flue temps I should be expecting, especially on start up. Up until now I've been using a digital laser thermometer, and reading stove top temps to regulate when I start cutting down the air on the stove, and I've been very pleased with how the stove has been running using this method, but it would be nice to know how hot the flue is (and how hot it should be) as well.

In the interest of full disclosure, you might notice that the flue temp readout is in degrees Celsius, but not to worry, I have a nice chart hanging on the door for quick and easy conversions....

razerface said:

i get up to 1300 and sometimes 1400 if not paying attn on my digital in a double wall. This is on startup, then i close it down and it goes to about 600-800,,, then slowly goes down as the load burns. I think my alarm is set at 1090 to give me time to get to the stove, which can get up to 1200-1300 in less then 45 more seconds. I never let it hold those temps.

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So do you use the flue temps to guide you in turning down the air, as opposed to stove top temps?

DougA said:

My probe is immediately after the stove, so my readings will be higher than if the probe was higher in the pipe. My alarm is set at 900 and it can jump way above that if I take more than 30 sec. to reach the stove to turn the air down. This is at start-up or refilling.
My normal running temps are about 100 higher on stove top than flue. ie: right now stove top is 600, probe in flue is 515
The type of stove (cat/non-cat) will affect the differences.

Yes, since getting the probe, I only occasionally glance at the stove top thermometers. I gauge everything on the probe.

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Thanks Doug. I just fed the stove with a small load after posting this thread, and I'm finding that the stove top is running about 30 degrees hotter than the flue now that it's settled down to cruise mode. I should also mention that I put the thermocouple at about 4' above the stove top (to avoid tripping hazards with wires etc). It was interesting watch the flue temps while I was starting up the burn; I continued using stove top temps to guide me in shutting down the air (start shutting down air at 250 degrees).... The flue temps peaked out a bit over 650 before settling back down into cruise mode..... All looking good....

razerface said:

I run 500-600 deg stovetop.

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Yeah, since I've started turning the air down earlier that's where I've been able to keep the stove top as well. I just feel like I'm burning more efficiently at those temps (in other words, I'm aiming to maximize my burn times this way)

Thanks for the help!

WES999 said:

I have something similar, I start turning down the air when the flue temp reaches 875, actually the stove turns down the air automatically . I also use flue temps and not stove top temps for when to turn down the air.
I like to keep flue temp under 1000, as that is what is is rated for, (continuous operation.)

I think you get the stove up to temp faster if you close the air in small increments to keep the flue temp around 900

One thing, I think your probe is installed a bit to high on your pipe, 18" above the stove is fairly typical.

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Hey Wes, are you the fella I remember that has the pulley system hooked up to automatically adjust the air control? Regardless, I think automatic air control is a very cool idea.... Pics are always nice to see though, hint hint.... I have to say that I really like the digital readouts your using. The look nice and clean and professional, as in an insurance inspector would nod approvingly at your set up for sure, whereas he might start clucking his tongue looking at the old temp controller I'm using with open/visible connections. Over the last year or so I've been mightily tempted to buy the Auberins TC readout, but maybe I can just build a nice little box that I can mount this controller/readout into....

As far as the extreme height of the probe in the flue, well I just wanted to run everything high enough overhead so that I could walk comfortably underneath the thermocouple/electrical wires, thus avoiding tripping hazards. I really just wanted to confirm that using stove top temps was working well and that I wasn't generating way too high flue temps by operating the stove that way....

So when l loaded up the stove on a nice bed of coals last night for the overnighter, I turned the air down to about 25% open when the stove top reached 250 - 300F (I can't remember what the flue temp was at that time), and then spent the next 5 - 10 minutes tweaking the air down lower and lower by very tiny increments (very slow lazy flames, just above the point of extinction, is my goal when adjusting the air at this point); over that 10 minute period the flue got as high as 850F, while the stove top ranged from 690 - 725F, depending where I took the temp. Once the air was shut down and the stove was cruising to my satisfaction I signed off and bid my baby (my stove) sweet dreams.... This morning at 6:30 the Ecofan was purring away while the flue was running about 220F and the stove top was around 190 - 200F with a nice bed of coals all ready to restart the next fire...

Thanks for the feedback Wes, and feel free to post a few more pics of your automated stove if you're so inclined....

Cheers

Wes, that is just an awesome set up (it is indeed the one I remember so well)! I love the videos too. I remember when I first saw it, I had just started data logging and graphing the burn cycles of my first stove; my wife was trying real hard to look interested and be supportive as I took her minute by minute through the last nights burn cycle, but after about the umteenth seminar, she was also starting to take an unusual interest in going upstairs to do the dishes..... and then you posted on a thread with pictures of your automated stove, which I immediately had to show her... Well I thought she was going to lose it, LOL I think she was afraid that I was going to try and do the same thing with my little stove I eventually reassured her that I wasn't at that stage (yet), and she couldn't help but agree that the members of Hearth.com were a mighty clever, albeit certifiable, group of enthusiasts. The thing is, I could tell that she really was just as impressed with your set up as I was......

Cheers

I can't wait to show the wife the videos tonight!