flue thermometer location

[Ashful]

So, I got two (one for each stove) Condar Medallion magnetic flue thermometers for single wall pipe, and they instructions state to place it 12" above the top of the stove. Well, I can't get right at 12", because my top load doors would hit the thermometers. So, I screwed one to the stovepipe on one of the stoves at 13". The other I just stuck in place with the magnet and no screw, until I see how they work at that height.

My initial impression is that this is way too low for a thermometer on a catalytic stove. When in bypass, flame can lick up the pipe a bit, and this low on the pipe tends to shoot pretty easily into 750F territory. Just a few inches higher, that same pipe is reading 600F, which is my normal max pipe temperature at time of cat engagement.

I do remember Dennis stating he had his close to 18" above the stove. For the rest of you, particularly the catalytic stove operators (I'm assuming non-cat's don't have a bypass damper, so an entirely different situation), at what height do you place your flue thermometers?

I did read one thread stating the flue surface thermometers were calibrated for a specific height above the stove. That makes no sense to me. Thermometers should (and I verified these do) measure the temperature of the surface to which they're attached, where ever that may be.

 

[AppalachianStan]

I have mine at 18". But Condar dose say at 12". I still have my pack for my ChimGard thermometer.

 

[AppalachianStan]

I say I would see higher temp at 12" then 18". Hmm?

 

[HotCoals]

I have mine around 18".
It seems fine there as a reference.
Even at a certain height move the thing in diff places around the pipe and you will get significantly diff readings.
I go more with my cat probe gauge. But mostly I just char up a new load then put the t-stat on 2 or less then forget about it.
No worries about over fire..noway.

 

[Ashful]

I say I would see higher temp at 12" then 18". Hmm?

Once your stove reaches steady state, cat engaged, the difference between 12" above the stove and 18" above the stove should be pretty minimal. I just checked mine, and there's a 9F difference.

However, when the stove is rapidly heating in bypass mode during the start-up cycle, there can be a 100 F difference in that same space.

I have mine around 18".
It seems fine there as a reference.
Even at a certain height move the thing in diff places around the pipe and you will get significantly diff readings.
I go more with my cat probe gauge. But mostly I just char up a new load then put the t-stat on 2 or less then forget about it.
No worries about over fire..noway.

Yeah, this is only for startup cycle. Once cat is engaged, the flue temp drops to 250F, and stays there for most of the burn cycle. I really only watch the flue temp while getting the stove heated up, and since these are downdraft cat stoves, the cat probe is 100% useless prior to closing the bypass damper.

 

[Highbeam]

In testing with my IR thermometer I find a dramatic uptick in surface temp of single wall pipe between 18" and 12" above the stove. My double wall cat stove pipe has a probe meter which is supposed to be at 18" above the stove which seems to be a much more logical representation of actual flue temps.

I think you are right that the meter simply reads surface temps. What are you trying to accomplish? If you are using the readings to protect your flue from overfire then you should conservatively leave it at 13". If you are trying to maintain a non-creosote forming higher temp in the flue then you would be conservative to place it higher on the pipe.

In my shop non-cat stove with single wall I am not concerned with overfiring the flue within 18" of the stove but I really want to be sure that enough heat is going up to prevent condensation so I mounted my surface temp meter on the single wall flue of my shop stove at 18". I lose 150 degrees of surface temp before it even hits the class A.

 

[AppalachianStan]

I may need to play with this. I have 2 of the ChimGards. I will put one at 12" and one at 18". I try to get the single wall stove pipe up to 300* before I close the by pass at 18". I always have low temp on the stove pipe when the by pass is close and the cat probe is at 1000*.

 

[HotCoals]

In testing with my IR thermometer I find a dramatic uptick in surface temp of single wall pipe between 18" and 12" above the stove. My double wall cat stove pipe has a probe meter which is supposed to be at 18" above the stove which seems to be a much more logical representation of actual flue temps.

I think you are right that the meter simply reads surface temps. What are you trying to accomplish? If you are using the readings to protect your flue from overfire then you should conservatively leave it at 13". If you are trying to maintain a non-creosote forming higher temp in the flue then you would be conservative to place it higher on the pipe.

In my shop non-cat stove with single wall I am not concerned with overfiring the flue within 18" of the stove but I really want to be sure that enough heat is going up to prevent condensation so I mounted my surface temp meter on the single wall flue of my shop stove at 18". I lose 150 degrees of surface temp before it even hits the class A.

Good post.
For me anyways I would not change anything much if I did think my flue was too cool,other then checking the pipe more then once a season.
I am going to change to double wall off the stove though by next season.
These cats do burn a cooler flue no doubt. 4th season on it and no creosote that alarms me when I clean it once a season.
The cap gets more then the pipe.

 

[Ashful]

I think you are right that the meter simply reads surface temps. What are you trying to accomplish? If you are using the readings to protect your flue from overfire then you should conservatively leave it at 13". If you are trying to maintain a non-creosote forming higher temp in the flue then you would be conservative to place it higher on the pipe.

Interesting reply, Highbeam. In my case, I'm only trying to avoid a glowing flue pipe, while in bypass waiting for a fresh load to get ready for cat engagement. I find the pipe (mostly on the 27 foot chimney, not so much on the 15 foot chimney) wants to soar right up to 750+ territory, if I leave the air control wide open long enough to get the stove where I need it for cat light-off. With the flue thermometer, I can start lowering the air control when the tube hits 500F, and thus avoid pipe temps over 600F.

I may need to play with this. I have 2 of the ChimGards. I will put one at 12" and one at 18". I try to get the single wall stove pipe up to 300* before I close the by pass at 18". I always have low temp on the stove pipe when the by pass is close and the cat probe is at 1000*.

I think this might be a factor in some of your other troubles, Stan. I have one stove that gives me lots of trouble with light-off and back-puffing, and another identical stove that gives me almost no such troubles. The only difference between the two is chimney height, and thus draft. The stove on the shorter chimney sometimes takes a looooong time for the stove pipe to reach 500F, cruising quite a long time in the 350F range. If I engage the cat with a stove pipe any cooler than 500F, the cat seems to stall out. The other stove... opposite scenario.

Good post.
For me anyways I would not change anything much if I did think my flue was too cool,other then checking the pipe more then once a season.

No trouble here. Even with the very marginal wood I was burning my first two years, my pipes stay very clean. I'm either burning very hot (in bypass mode) with flue pipe running 350 - 700F, or I have a cat engaged and cruising at 1000F - 1500F with pipe at 250F. That doesn't give creosote too much chance to form.

 

[HotCoals]

As soon as my cat temp is above active I close the by pass but leave the air up till the cat temp is about half on the scale.
Cat still looked like new before the start of the season. I don't have the air so high on start ups though that the flames are licking the cat to death so to speak..lol.

 

[Highbeam]

Interesting reply, Highbeam. In my case, I'm only trying to avoid a glowing flue pipe, while in bypass waiting for a fresh load to get ready for cat engagement.

We can work with this. Due to the temperature gradient you know the hottest spot on the flue is right at the collar. The flue won't all turn red at once, it will start at the hottest part and climb. Set your meter as low as possible and yes, the flames flying up from the bypass are a factor, it doesn't matter why it's hot.

 

[HotCoals]

I may need to play with this. I have 2 of the ChimGards. I will put one at 12" and one at 18". I try to get the single wall stove pipe up to 300* before I close the by pass at 18". I always have low temp on the stove pipe when the by pass is close and the cat probe is at 1000*.

Most cat stoves will have low flue temps in cruise...that's how we get the long burns.

A good cat will clean up the smoke before it gets to the flue if the wood is dry.

 

[AppalachianStan]

18' of chimney, 8" flue and wood between 15 and 19%. It can take me up to 30 mins or longer to get stove pipe to 300* and cat probe up to 800* at the same time. I always have to live the door open to do this. Close door wait a min or two( most of the time flames go out) then close down the by pass to about a 1/4" wait a min or two no flames with the prime air open all the way and temps will drop to 600*. Re-pet until I can keep 800* temps on the cat probe. in a hour or two the temps will hit 1000* it will say here for about 2 hours.This is always the way the stove dose on start up or reload. If I would let the Flue get to 500* most of the wood would be gone. By the way I have only seen temp at 1500* twice

 

[Ashful]

As soon as my cat temp is above active I close the by pass but leave the air up till the cat temp is about half on the scale.
Cat still looked like new before the start of the season. I don't have the air so high on start ups though that the flames are licking the cat to death so to speak..lol.

My stoves are downdraft catalytic, so there are never flames licking the cat. In bypass mode, there is a door open at the top rear of the firebox, which goes straight to the flue. When the door is closed, exhaust must exit the firebox thru a pair of openings in the rear wall toward the top of the firebox, travel down thru a cast iron and refractory plenum, then go back up thru the cat to reach the flue. It's the ultimate design for avoiding flame impingement and ash clogging (you will NEVER find fly ash on the cat in this stove), but the round-about exhaust path does make achieving initial light off a little more difficult. Also, since no exhaust travels thru the cat prior to closing the door, the cat probe usually shows 100F right up to the time you close the bypass, no matter how hot and long you run the stove in bypass.

18' of chimney, 8" flue and wood between 15 and 19%. It can take me up to 30 mins or longer to get stove pipe to 300* and cat probe up to 800* at the same time. I always have to live the door open to do this. Close door wait a min or two( most of the time flames go out) then close down the by pass to about a 1/4" wait a min or two no flames with the prime air open all the way and temps will drop to 600*. Re-pet until I can keep 800* temps on the cat probe. in a hour or two the temps will hit 1000* it will say here for about 2 hours.This is always the way the stove dose on start up or reload. If I would let the Flue get to 500* most of the wood would be gone. By the way I have only seen temp at 1500* twice

Let's keep this issue to your thread, and not muddy up another thread with the same facts already stated elsewhere. I suggest anyone wanting to discuss the issues with your Appalachian 52 go here: https://www.hearth.com/talk/threads/back-puffing.117696/page-5#post-1625768

 

[AppalachianStan]

Sound good to me Joful.

 

[HotCoals]

My stoves are downdraft catalytic, so there are never flames licking the cat. In bypass mode, there is a door open at the top rear of the firebox, which goes straight to the flue. When the door is closed, exhaust must exit the firebox thru a pair of openings in the rear wall toward the top of the firebox, travel down thru a cast iron and refractory plenum, then go back up thru the cat to reach the flue. It's the ultimate design for avoiding flame impingement and ash clogging (you will NEVER find fly ash on the cat in this stove), but the round-about exhaust path does make achieving initial light off a little more difficult. Also, since no exhaust travels thru the cat prior to closing the door, the cat probe usually shows 100F right up to the time you close the bypass, no matter how hot and long you run the stove in bypass.

Interesting...sounds like a well thought out stove.

 

[Ashful]

Interesting...sounds like a well thought out stove.

In many ways, yes. There are trade-offs and compromise in every design, though!