Is a stove top thermometer enough or do I need a flue thermometer as well for my new GM 60?

[cabinwarmer]

Hello All, I am working on my third week with this new stove and am wondering if my STT is providing enough information to me? I use the STT along with the CAT meter at this point, any thoughts? I have a double wall pipe, so a probe would be required. Is using both thermometers over kill?

Thanks for your thoughts,

Dave

 

[begreen]

Of the 3 options, I find the stovetop temp the least useful, unless I am cooking or boiling water on the stove. In a non-cat, the flue temp is much more meaningful to me. As long as I keep that properly regulated there is no chance of overfiring the stove, which seems to be the main reason people want a stovetop thermometer. Since I added the Auber digital probe last year, I barely look at the other thermometers except to provide feedback to people here when requested.

 

[Highbeam]

Especially since you’re now burning a hybrid cat stove type thing, I would not value the reading from a stove top meter. That cat should be cruising along at 1500 which makes the stove top temperature simply a matter of where you place the meter. A probe meter is pretty great. Tells you when you are under firing tells you when you are over firing. And tells you when you are happily somewhere in the middle.

Higher flue temps mean more heat but less efficiency, lower flue temps mean less heatbut higher efficiency.

It doesn’t hurt to leave the stove top meter there but the value of that reading is just a double check.

 

[cabinwarmer]

Interesting, any recommendations on a flue probe unit? I do not think I need the 110v models with alarms. I understand they should be 18 inches above the stove, correct? And, what temp would you be happy with for this GM 60 ? Rockford site says 400-900F, seems like a rather large range.

Thanks gentlemen, Dave

 

[Nigel459]

I use a flue meter on my gm40. Just the standard condar one. Google should find it.

When flue temp is >500 you know you can safely flip to the cat if the fire is somewhat established. It’s usually much earlier than the cat meter says active.

I don’t bother looking at stove top temp much anymore.

 

[cabinwarmer]

Thanks Nigel, I do see a condor on Amazon. Funny story, I just hung up with my local "stove shop". They said just get a heat gun. I tried to explain to him that would not measure gas/flue temps. His response was there is a relationship between outside pipe temp and flue temp. I struggle sometimes........with my patience.

 

[Highbeam]

Thanks Nigel, I do see a condor on Amazon. Funny story, I just hung up with my local "stove shop". They said just get a heat gun. I tried to explain to him that would not measure gas/flue temps. His response was there is a relationship between outside pipe temp and flue temp. I struggle sometimes........with my patience.

Not on double wall pipe. Outside temps are only slightly relevant. The condar brand probe meter is very appropriate. Looks pretty good and you can monitor it from your couch!

That wide 400-900 range of good flue temperatures is a good thing. It gives you the leeway to operate the stove to match your needs as best you can.

 

[tabner]

@Nigel459 if you flip the cat active around 500+ on the flue temp, roughly where does your flue temp settle in after that? As in an hour or two into a burn with catalyst engaged, I'm just wondering what kind of flue temps the GM runs at. Or does it vary widely based on how you're running the stove?

 

[Nigel459]

Good question. I try to run the stove as low and long as possible. Sooo,

I flip into cat mode as soon as possible, ie as soon as flue hits 500 (probes can lag a bit so sometimes I just know it’s hot enough even as the probe is still climbing). Then usually the flue probe goes down to 400 as the stovetop climbs big time. The flue will cruise at 400 while I burn in the load (depending on the wood 5-15 mins) and then when I turn it down for a long burn it will drop a bit, probably to 300-325 for most of the burn.

 

[Highbeam]

Good question. I try to run the stove as low and long as possible. Sooo,

I flip into cat mode as soon as possible, ie as soon as flue hits 500 (probes can lag a bit so sometimes I just know it’s hot enough even as the probe is still climbing). Then usually the flue probe goes down to 400 as the stovetop climbs big time. The flue will cruise at 400 while I burn in the load (depending on the wood 5-15 mins) and then when I turn it down for a long burn it will drop a bit, probably to 300-325 for most of the burn.

Thats a cold flue. Below the recommended temperature. I’m actually impressed that the hearthstone offers that much control.

Flue temperatures of 300 mean surface temperature of 150 which is below the condensation temperature of water so be careful that you’re not gunking up the chimney! I’ve done it, it’s gross.

The GM stoves look good and it would be great if they performed as marketed.

 

[Nigel459]

Thats a cold flue. Below the recommended temperature. I’m actually impressed that the hearthstone offers that much control.

Yes I do use a fairly restrictive damper to fight the bungalow syndrome...

Flue temperatures of 300 mean surface temperature of 150 which is below the condensation temperature of water so be careful that you’re not gunking up the chimney! I’ve done it, it’s gross.

The GM stoves look good and it would be great if they performed as marketed.

Hmmm those flue temps and behaviour after engaging cat is almost identical to what the BK did on the very same flue. I've never gunked things up, even with marginal wood my first season... maybe my flue probe is mis-calibrated.

My flue is a bunch of double-walled connector up to the cathedral ceiling then only like 6 feet of class A, maybe only 4 feet of it outside so maybe I'm lucky and my flue stays warm. I even have a screen, which has never gotten even close to gunky.

 

[begreen]

I don't mean to sell a product, but the difference between an analog probe thermometer and a digital one is huge. Since running with the digital probe, the Condar feels like getting flue temps via a slow email connection. With the digital probe, I can see the effect of changing the air control in real-time. It's a major difference.

 

[cabinwarmer]

I would like to go digital, but seem to not find much of a selection. Recommendation? Do all the digital probes require 110v?

 

[Tron]

Thats a cold flue. Below the recommended temperature. I’m actually impressed that the hearthstone offers that much control.

Flue temperatures of 300 mean surface temperature of 150 which is below the condensation temperature of water so be careful that you’re not gunking up the chimney! I’ve done it, it’s gross.

Sorry about hijacking the thread, but this gets me interested. I'm currently running my BK quite low as not to be baked out of my living room. Like around 1 o'clock on the thermostat. That is after the fire is established and the cat has heated up, of course.

Now I have a Condar flue thermometer in my (6"-double-walled) flue, about 20" above the stovetop, and once the stove settles to cruising I only read about 200F, with the cat thermometer well into the active range. Not sure how accurate the Condar really is, but should I be worried? Last season we only ran the stove for 1-2 months as we installed it in February, in the same manner, and only got half a handful of (dry) deposits out of the flue when we cleaned it in fall.

If I turn the stove up, the flue temperature rises as well, as expected.

Wood is well-seasoned, mostly pine, MC well below 20%.

 

[Nigel459]

I don’t think it’s hijacking since the thread topic is the need for flue thermometers...

My BK runs the same, with a very cool flue. I haven’t had any issues with creosote, just a normal amount prob from startups and so on.

I think one can judge how cleanly one’s stove is running by: observing emissions ie watching for smoke; keeping an eye on the cap, which gets gunky first; and, observing your sweepings/cleanings.

Sounds like you’re doing just fine

Sorry about hijacking the thread, but this gets me interested. I'm currently running my BK quite low as not to be baked out of my living room. Like around 1 o'clock on the thermostat. That is after the fire is established and the cat has heated up, of course.

Now I have a Condar flue thermometer in my (6"-double-walled) flue, about 20" above the stovetop, and once the stove settles to cruising I only read about 200F, with the cat thermometer well into the active range. Not sure how accurate the Condar really is, but should I be worried? Last season we only ran the stove for 1-2 months as we installed it in February, in the same manner, and only got half a handful of (dry) deposits out of the flue when we cleaned it in fall.

If I turn the stove up, the flue temperature rises as well, as expected.

Wood is well-seasoned, mostly pine, MC well below 20%.

 

[Highbeam]

Sweep the chimney often when you are just starting out and especially when flirting with such low flue temperatures around the condensation point.

The condar flue probe says right on it that your flue temperature below 400 is Too Cool for a reason.

Look for visible emissions and actual drops of drooling tar landing on the storm collar of the chimney. It’s a mess to clean up.

These stoves do low and slow better than anything but there is a limit. You’re on the ragged edge.

 

[jmb6420]

Auber is having A Thanksgiving sale until the 30th.
Even though date says 10/30 the sale prices are posted on site.

Thermometer for Stove Pipe,Chimney,Outdoor Wood Boiler,w/ Alarm Thermometer for monitoring temperature on stove, chimney, or outdoor wood boiler [AT200CHIM] - $79.99 : Auber Instruments, Inc., Temperature control solutions for home and industry

This thermometer kit can be used for monitoring the temperature in stove pipes, chimneys, and outdoor wood boilers. This thermometer reads a thermocouple probe, shows the temperature on its red LED display, and makes a buzzing sound when temperature rises above the pre-set alarm temperature. For...

www.auberins.com

 

[begreen]

I would like to go digital, but seem to not find much of a selection. Recommendation? Do all the digital probes require 110v?

I am using the Auber AT200. It has made a big difference in the way I run the stove. I no longer rely on the Condar probe. It's much too slow and not very accurate. Feels like getting the flue temp via slow email. With the digital probe, you can see the effect of changing the air in realtime.

Thermometer for Stove Pipe,Chimney,Outdoor Wood Boiler,w/ Alarm Thermometer for monitoring temperature on stove, chimney, or outdoor wood boiler [AT200CHIM] - $79.99 : Auber Instruments, Inc., Temperature control solutions for home and industry

This thermometer kit can be used for monitoring the temperature in stove pipes, chimneys, and outdoor wood boilers. This thermometer reads a thermocouple probe, shows the temperature on its red LED display, and makes a buzzing sound when temperature rises above the pre-set alarm temperature. For...

www.auberins.com

 

[cabinwarmer]

Yes the 200 seems to be the one. Not sure of all the wiring, but you can't have everything. Safety first I suppose. I have a Condar analog on order at this point, but may change that to a 200.

 

[Tron]

There were no "wet" deposits when we swept the chimney. No visible tar drops on the storm collar, either.

I only see visible smoke emissions when starting up or after a reload (cat off, so that's to be expected). Once hot and turned down, I occasionally see wisps of steam condensing in the cold (and humid) morning air, but that's all. No visible steam once the sun is up and has warmed the air up a little. But then, it's been sunny here for the last 4 weeks or so, I'll see how that behaves when it's cold and cloudy.

 

[Nigel459]

Yeah same here, never have I seen any “wet” tar anywhere even with my low flue temps. On either of two setups with the BK and now with the GM40. Heck my cap with screen has never needed a cleaning let alone deposits on flashing or storm collars. Again, maybe my flue probe is a bit off.

It seems to me I really would have to be smouldering the fuel load to get anything gunked up. Some guys up north I know do smoulder in their non-cats and yeah, I have seen the gunk!

As we often say around here, every setup is different, from fuel type, MC, air temp, atmospheric pressure, humidity... etc... I guess I can count myself lucky.

@Highbeam maybe that old stone stove of yours was prone to gunk, hard to get up to clean burn temp or something? Or have you seen gunk with the BK as well?

There were no "wet" deposits when we swept the chimney. No visible tar drops on the storm collar, either.

I only see visible smoke emissions when starting up or after a reload (cat off, so that's to be expected). Once hot and turned down, I occasionally see wisps of steam condensing in the cold (and humid) morning air, but that's all. No visible steam once the sun is up and has warmed the air up a little. But then, it's been sunny here for the last 4 weeks or so, I'll see how that behaves when it's cold and cloudy.

 

[Highbeam]

Yeah same here, never have I seen any “wet” tar anywhere even with my low flue temps. On either of two setups with the BK and now with the GM40. Heck my cap with screen has never needed a cleaning let alone deposits on flashing or storm collars. Again, maybe my flue probe is a bit off.

It seems to me I really would have to be smouldering the fuel load to get anything gunked up. Some guys up north I know do smoulder in their non-cats and yeah, I have seen the gunk!

As we often say around here, every setup is different, from fuel type, MC, air temp, atmospheric pressure, humidity... etc... I guess I can count myself lucky.

@Highbeam maybe that old stone stove of yours was prone to gunk, hard to get up to clean burn temp or something? Or have you seen gunk with the BK as well?

Oh, the stone stove left my chimney much cleaner than the BK. Lots of heat dumping up the chimney that one!

Since I go through a cat every two years and seemingly never at the end of the season my tar drips are probably from a dead cat. They do not come off.

I also have a well used but perfect looking condar meter. I might be a good candidate for one of those fancy at200 meters at least for testing. Wife would not appreciate a wire sticking out of the pipe in front!

We all agree, go out and look at your chimney. No smoke, it’s all good. Sweep frequently at first to verify it’s all good.

 

[MMH]

Agree with everyone here and I have a bit of thoughts myself. Is STT useful data? Maybe maybe not. Lots of variables including where you put it. One area of your stove may be warmer than other area etc. It would be useful perhaps for cooking but otherwise I’d agree with everyone here. I have a magnetic therm on stove top, I still look at it but I don’t put as much weight on it compared to when I first got our stove.

Now this is where I’ll probabaly catch some flak. Is another therm overkill (ie adding a pipe probe etc)? Absolutely not. The more data the better (assuming its useful and not shinfo). However I do not have one. When we first got the stove I had 2 magnetic stove top therms so I stuck one on the pipe (18” up etc), with the intention of buying a probe. After doing some research and from others here of course, the analog probes are only rated for a few thousand hours of use (don’t remember exactly) and for full time burners that’s not a lot of time; so for me it didn’t seem worth drilling a hole and sticking a probe in it that I can only trust for a small amount of burning time (looking ahead to future). An option would be replacing it every year or two (depending on life cycle). Now then the answer becomes a digital probe. I think that’s a good investment if you want it. Someone else could chime in on their digital ones for life span etc. My wife and I also didn’t seem to keen on the idea of a wire hanging out of the pipe and running to closest outlet etc. So, I don’t have one.

Now, is a probe/pipe therm a good idea? Sure. Does it give useful data? Absolutely. Is it required? I’d say not necessarily. I use this magnet one; is it accurate for my flu gasses? No. But, I’ve gotten used to where I normally see it at, and what is to high based on how the stove and pipe behaves and where it sits when the stove is cruising etc. So, I can start turning down and dialing in with it and it works for me. I will say that in the argument of real time data and honestly in any other argument probabaly a digital probe is the way to go. I’m just not convinced that it’s a 100% requirement (no disrespect to anyone here).

So, in conclusion, if you want one and have the money get one. If you feel like it’s the best way to go (which is likely right) then get one.

 

[begreen]

I've burned for decades without a digital probe and yes, if you are astute and watch the fire, you can do without it. I can say the same for firewood. I only picked up a moisture tester a couple of years ago, mostly to verify and be accurate here. But not everyone knows how to watch a fire or test wood manually.

Our flue has always been very clean. We get less than a cup every two years. With the digital probe, I now see why. Going by the analog probe I was closing down the air much later, wasting heat up the flue. If one goes back to around 2007 I posted a thread on the Castine and how I was noting that waiting for the stovetop to get up to temp was unnecessary and inefficient. I was finding that with dry wood I could start closing down the air with the stovetop just at 200-250º. This was based on watching when secondary combustion started, which is pretty showy in the Castine. The reason is that it takes a lot longer to warm up the thick cast iron than it does to reach secondary burn temp in the firebox. Since then I have not gone by SST for timing air control closure and started going by the probe temp. At this point, I was burning in the T6. This worked well enough, but I still was seeing a very strong fire before shutting down the air. So I started experimenting with closing it down with the flue temp around 400º or so and that worked fine. Again, on a cold start, the stovetop temp lagged way behind the probe reading. It was and is a much less meaningful metric than flue temp due to the long lag.

Re digital probe wiring. Yes, it is visually messier. I have the Auber down low to minimize visual impact. My wife was dubious at first but now she really likes it because she can see in real-time how the fire is burning and have a temperature verification that she is keeping it hot enough. My son is more technical and he really likes the precision because he is less likely to look at the fire than at the instrument. With the deep firebox of the T6, it's possible to have a strong fire at the back of the stove and yet be visually blocked by the wood in front. In this circumstance, the digital readout is essential if one doesn't want to waste wood up the flue. All of us like the alarm feature. It is too easy to get distracted and miss turning down the stove. The alarm really helps keep us on top of things.

 

[Tron]

Ok, so to verify the Condar's temperature I inserted my professional cooking probe into the flue. That's precise to about a degree or two.
Turns out that when the Condar shows 200F (as far as a correct reading is possible there), the real flue temperature is around 320F.

So well above the boiling point of water, but then again the probe location is only 2 feet above the stove, and the temperature will drop further along the flue...