2023/24 VC Temperature discussion thread

[AsylumResident]

your secondary air is always full open, nothing to see. the 2n1 designs do not have active secondary air control.

Why did I think it did? Rhetorical question, but that just makes so many more questions now.

So if it's always completely open, it's rate of intake is entirely dependent on draft?

 

[AsylumResident]

I dont ever open up the stove. I have Never altered the course of it neither. I 100% let the stove do its thing. This is just my experience... and I haven't had alot of them either..

Most recently my cat temperature climbed to 1670. It never hangs at a peak temperature like that long. maybe 5/10 minutes.. then drops down and even it stayed there for 15 or so.. nothing really happens.

The only thing actually happening is killing the life of the cat. Me personally I don't see Crazy stovepipe temperatures in my double wall pipe.. Iv had the stove apart and the back of the stove is protected with insulation board so its not like the stove is going to crack

I just let it run its course never lasts long never any damage to the stove itself or stovepipe

Im definitely open to this discussion of why people get alarmed regarding this besides the damage to the cat what else could be a issue.

I know its unsettling and we want all of our temperatures to stay 1200 degrees, but why not just let it run its course

@arnermd whatnare your thoughts you probably have the most experience in this

So when my cat reaches 1800, nothing inside the stove, including the fire back or refractory engine (I think that's what it is called) is in jeopardy? Just my cat?

The other, more unsettling, thing to me is the flue gas temp when the cat reaches 1800. Flue gasses registering around 1200-1300 won't due any damage to the flue? I get that hot metal smell but nothing overly dangerous is happening?

I know you can't get tone from reading text but I'm legitimately asking. Right now I am making assumptions that something relatively dangerous is happening, or at least some sort of damage is happening when hitting those high temps. Stop worrying so much about it?

 

[arnermd]

Why did I think it did? Rhetorical question, but that just makes so many more questions now.

So if it's always completely open, it's rate of intake is entirely dependent on draft?

yep..... Although there are some other things that may be affecting it.... I have thought a lot about this over the years and my ultimate conclusion is I would rather have thermostatic control on the secondary air. Although folks with the older stoves have cat issues too..... I think it is less likely however (my opinion of course and I would absolutely love to hear from a VC designer on why they made the design choices they did with the 2n1 design)

But I digress..... Other things can affect secondary air flow, according to me....haha

• Draft is the obvious one and the key driver. Draft level is dictated by temperature in the stove pipe vs outside temp.
• Position of the damper: With the damper closed the pressure in the firebox will be higher as the secondary flow path is more restrictive, thus less secondary flow.
• Position of the primary inlet flapper: As the primary air flapper closes the pressure in the firebox / secondary will go more sub ambient. So secondary air will increase as the primary air flow goes down.
• Sizing of the EPA holes and any leakage: The more leaks the lower the secondary air flow will be
• Preheating of the secondary air in the refractory: If the secondary air increase temperature before it hits the restrictions in the refractory the mass flow of the secondary air will go down. So as the refractory gets hotter it tend to decrease the air flow via preheating.

Then there is the question of degree, some of these are probably minor some are major influences on the secondary flow rate

All just my opinion of course.... I welcome any corrections or alternative viewpoints.

 

[arnermd]

So when my cat reaches 1800, nothing inside the stove, including the fire back or refractory engine (I think that's what it is called) is in jeopardy? Just my cat?

The other, more unsettling, thing to me is the flue gas temp when the cat reaches 1800. Flue gasses registering around 1200-1300 won't due any damage to the flue? I get that hot metal smell but nothing overly dangerous is happening?

I know you can't get tone from reading text but I'm legitimately asking. Right now I am making assumptions that something relatively dangerous is happening, or at least some sort of damage is happening when hitting those high temps. Stop worrying so much about it?

I have spent many a night tending a nuclear stove pondering these very same questions..... I have reached out to VC in the past and got no response to these questions. I would dearly love to hear from them.

I think when we talk max temp capability there are a few things to keep in mind.

• It is not just temp but also the time at that temp. Spiking up to 1650F for a few minutes is not the same as cruising at 1650 for hours....
• Rate of change can also be a factor, i.e thermal shock. Obviously rapid changes in temps are harder on materials than slow changes.

Flue temps:

• You are measuring gas temps, not metal temps, so I would expect elevated readings, 1200-1300 is pretty hot but my guess is unless you hang there for a while (tens of minutes?) you are not doing any real damage. Don't get me wrong, I think that's really hot and warrants your attention..... and you should try to avoid it if possible....
• Found this: https://www.hearth.com/talk/wiki/what-is-a-safe-flue-temp-what-is-too-hot/

Cat temps:

• I think we all agree that 1500 - 1600+ cat temps are damaging to the cat. The longer you stay there the more life you take away from the cat. In my experience metal cats hold up better than ceramic cats at these temps and metal cats also result in lower peak temps (usually). I personally don't really care anymore, If i need to replace the cat every year I am fine with that, they are relatively inexpensive and easy to replace in the 2n1 design and I can run without one in a pinch.
• I am much more concerned with the refractory (expensive and hard to replace) and my personal opinion is that at 1600+ it is accelerating the aging of the ceramic. How much I do not know....
  • As we all know I am on my third refractory, but to be honest I am not sure what caused the first 2 failures. it may have been temperature, it may have been thermal shock. I don't know for sure.

So.... I am trying not to worry about cat temps in the 1650 range (my alarm is now set to 1700 cause I am tired of hearing it). I will just let it go, maybe tinker with air and draft but that's about it. If I get a real rager and temps are closer to 1700 I will put my plate over the secondary inlet and that usually kills it for the night. At some point my cat will die, I expect it and do not really care.....

Full disclosure: I have a full lifetime warranty on my refractory that VC has honored twice. So I worry less because of that. Although it requires a complete teardown to fix.

I will also add I never felt the stove was unsafe. (except maybe when flue temps go over 1000F, that's concerning, but happens very rarely and not for long). My cast iron temps have never run off and I have never seen glowing red cast iron.

This post is way tooo long.... as always this is all my opinion. Others welcome....

 

[arnermd]

I dont ever open up the stove. I have Never altered the course of it neither. I 100% let the stove do its thing. This is just my experience... and I haven't had alot of them either..

Most recently my cat temperature climbed to 1670. It never hangs at a peak temperature like that long. maybe 5/10 minutes.. then drops down and even it stayed there for 15 or so.. nothing really happens.

The only thing actually happening is killing the life of the cat. Me personally I don't see Crazy stovepipe temperatures in my double wall pipe.. Iv had the stove apart and the back of the stove is protected with insulation board so its not like the stove is going to crack

I just let it run its course never lasts long never any damage to the stove itself or stovepipe

Im definitely open to this discussion of why people get alarmed regarding this besides the damage to the cat what else could be a issue.

I know its unsettling and we want all of our temperatures to stay 1200 degrees, but why not just let it run its course

@arnermd whatnare your thoughts you probably have the most experience in this

I will try to keep this short......

• I have had cat temps cruise at 1600+ for over an hour or more.... Sometimes I try to bring it down, lately I just let it go.
• I will reduce airflow, sometimes that works to bring it back down, sometimes it drives it up. If it goes up I will increase airflow. Silly I know.....
• Blocking the secondary air flow completely has been effective lately, but it can take a while.

Opening up the griddle to shift wood around with a full load is a really bad idea.... I have done it too, it never ends well. A small load, yes you can get away with it. Dumping a ton of air into the firebox is not good and I would be concerned with the potential for thermal shock.

We all want our stoves to run good and last a long time and we are all willing to do what it takes to make it so.... but sometime these things are just inconsolable.

 

[JohnDaileyNH]

I dont ever open up the stove. I have Never altered the course of it neither. I 100% let the stove do its thing. This is just my experience... and I haven't had alot of them either..

Most recently my cat temperature climbed to 1670. It never hangs at a peak temperature like that long. maybe 5/10 minutes.. then drops down and even it stayed there for 15 or so.. nothing really happens.

The only thing actually happening is killing the life of the cat. Me personally I don't see Crazy stovepipe temperatures in my double wall pipe.. Iv had the stove apart and the back of the stove is protected with insulation board so its not like the stove is going to crack

I just let it run its course never lasts long never any damage to the stove itself or stovepipe

Im definitely open to this discussion of why people get alarmed regarding this besides the damage to the cat what else could be a issue.

I know its unsettling and we want all of our temperatures to stay 1200 degrees, but why not just let it run its course

@arnermd whatnare your thoughts you probably have the most experience in this

If mine goes high in to 1500 low 1600 I just let it run its course. I have found opening the window closest to the stove and letting fresh cold air in to the secondary will drove down cat temps. Thats my go to move now if my cat is out of control, but I haven't had to do that this year.

The more I've used the stove the more I've learned when to wait longer to reload to avoid a cat mess.

 

[JohnDaileyNH]

I have spent many a night tending a nuclear stove pondering these very same questions..... I have reached out to VC in the past and got no response to these questions. I would dearly love to hear from them.

I think when we talk max temp capability there are a few things to keep in mind.

• It is not just temp but also the time at that temp. Spiking up to 1650F for a few minutes is not the same as cruising at 1650 for hours....
• Rate of change can also be a factor, i.e thermal shock. Obviously rapid changes in temps are harder on materials than slow changes.

Flue temps:

• You are measuring gas temps, not metal temps, so I would expect elevated readings, 1200-1300 is pretty hot but my guess is unless you hang there for a while (tens of minutes?) you are not doing any real damage. Don't get me wrong, I think that's really hot and warrants your attention..... and you should try to avoid it if possible....
• Found this: https://www.hearth.com/talk/wiki/what-is-a-safe-flue-temp-what-is-too-hot/

Cat temps:

• I think we all agree that 1500 - 1600+ cat temps are damaging to the cat. The longer you stay there the more life you take away from the cat. In my experience metal cats hold up better than ceramic cats at these temps and metal cats also result in lower peak temps (usually). I personally don't really care anymore, If i need to replace the cat every year I am fine with that, they are relatively inexpensive and easy to replace in the 2n1 design and I can run without one in a pinch.
• I am much more concerned with the refractory (expensive and hard to replace) and my personal opinion is that at 1600+ it is accelerating the aging of the ceramic. How much I do not know....
  • As we all know I am on my third refractory, but to be honest I am not sure what caused the first 2 failures. it may have been temperature, it may have been thermal shock. I don't know for sure.

So.... I am trying not to worry about cat temps in the 1650 range (my alarm is now set to 1700 cause I am tired of hearing it). I will just let it go, maybe tinker with air and draft but that's about it. If I get a real rager and temps are closer to 1700 I will put my plate over the secondary inlet and that usually kills it for the night. At some point my cat will die, I expect it and do not really care.....

Full disclosure: I have a full lifetime warranty on my refractory that VC has honored twice. So I worry less because of that. Although it requires a complete teardown to fix.

I will also add I never felt the stove was unsafe. (except maybe when flue temps go over 1000F, that's concerning, but happens very rarely and not for long). My cast iron temps have never run off and I have never seen glowing red cast iron.

This post is way tooo long.... as always this is all my opinion. Others welcome....

I agree here. If my stove temp isn't out of control my concern is less. If I kill the cat I kill the cat

 

[NewGuy132]

I think you figured out the key information without realizing it. Great breakdown btw.
Here is what I think:
When you packed the stove full with the cat inside operation zone and a healthy bead of coals, all of that wood starts to bake and off gas. It's not burning except mabey the bottom layer and there is so much wood in the box, the flames don't get all the way to the top of the stove for combustion. The wood then absorbes the heat in the box preventing it from reaching the stove top (this explains the lower STT).
Your wood then is throwing a massive ammount of smoke and gasses into the 2ndary combustion chamber and your cat is rapidly trying to eat it all spiking the cat temps. The coals are keeping the smoke HOOOOT.

Now, how to fix and or prevent/manage that..... IDK
I have never had this problem. My draft has never gotten so strong where it sucks all of that smoke causing a runaway. Usually my stove top temp is directly related to my primary air control in the Duantless & how much wood is in my stove. It will always drop for me after a reload, then creeps back up over time.
Additionally, my flu temps never get over 300f unless my bypass is open regardless of the wood load and air control settings.

Thanks. I tried to keep on top of it and remember everything that I did. Most likely it was all of the wood off gassing at the same time one the deep bed of hot coals. I have a 30+ft chimney so I already have plenty of draft so I'm sure that didn't help the situation. I didn't have time for a fire last night, but I'll probably be back at it either tonight or tomorrow.

Do you think this happened because you did a full load on a large coal bed? Maybe since the stove and cat is already hot a full load can be too much fuel for the cat especially if the air is set too low and sending lots of smoke into that secondary burn chamber?

I think just about any stove has a better chance of overfiring with a large coal bed or hot reloads. I try and keep my coal bed to a minimum when I’m on a 8 or 12 hour reload schedule. Sometimes I’ll rake the coals and open the air full for awhile til it’s down to where I like it. Other times when it’s really cold out I don’t worry about the coal bed and just load a half load and burn a little hotter and load more often like you stated.

Yes this was probably all of the wood off gassing at the same time due to the bed of coals. I was home so I was doing 2-3 hours reloads of 2-3 large splits so there was quite the coal bed.

Just my experience when I reload over a real hot large coal bed and pack it to the top I cut the air back as soon as I close the damper. This cold snap I had one time where I didn't and the cat started to take off but I shut the air and rode it out cat quit at 1560.
Not familiar with your stove but it brings us back to secondary air intake questions. My stove has a secondary air intake flap on the back that is thermostatically controlled. It closes after first warmup and will open back as the cat gets to 1600.

Typically this is what I do when I'm just tossing in my usual 2-3 splits. This time I put in 6 or so and they stacked up to the damper flap. Also one of them fell right in front of the refractory so it was probably shooting flames back in to the 2ndary. My stove is also thermostatically controlled so aside from closing the air down there really wasn't anything I could do. I thought for a minute or two about taking some wood out and putting it in to a 5 gallon bucket of water, but that would have been a giant mess.

I dont ever open up the stove. I have Never altered the course of it neither. I 100% let the stove do its thing. This is just my experience... and I haven't had alot of them either..

Most recently my cat temperature climbed to 1670. It never hangs at a peak temperature like that long. maybe 5/10 minutes.. then drops down and even it stayed there for 15 or so.. nothing really happens.

The only thing actually happening is killing the life of the cat. Me personally I don't see Crazy stovepipe temperatures in my double wall pipe.. Iv had the stove apart and the back of the stove is protected with insulation board so its not like the stove is going to crack

I just let it run its course never lasts long never any damage to the stove itself or stovepipe

Im definitely open to this discussion of why people get alarmed regarding this besides the damage to the cat what else could be a issue.

I know its unsettling and we want all of our temperatures to stay 1200 degrees, but why not just let it run its course

@arnermd whatnare your thoughts you probably have the most experience in this

Opening the stove was probably the worst thing that I could do and I knew it right when I closed it. That cause the cat temp to take off like a rocket. I was thinking that I had a piece of wood back by the refractory shooting flames back in to the 2ndary. I could hear the afterburner sound. I wasn't sure that temp that cast iron melts at so that was my main concern(2200 if you were wondering). I don't care about replacing a cat even if I have to do it every year. I was just trying to see if I could get a 4 or so hour burn time out of my little stove so I wouldn't be doing a cold start every day.

 

[AsylumResident]

Thanks. I tried to keep on top of it and remember everything that I did. Most likely it was all of the wood off gassing at the same time one the deep bed of hot coals. I have a 30+ft chimney so I already have plenty of draft so I'm sure that didn't help the situation. I didn't have time for a fire last night, but I'll probably be back at it either tonight or tomorrow.



Yes this was probably all of the wood off gassing at the same time due to the bed of coals. I was home so I was doing 2-3 hours reloads of 2-3 large splits so there was quite the coal bed.



Typically this is what I do when I'm just tossing in my usual 2-3 splits. This time I put in 6 or so and they stacked up to the damper flap. Also one of them fell right in front of the refractory so it was probably shooting flames back in to the 2ndary. My stove is also thermostatically controlled so aside from closing the air down there really wasn't anything I could do. I thought for a minute or two about taking some wood out and putting it in to a 5 gallon bucket of water, but that would have been a giant mess.



Opening the stove was probably the worst thing that I could do and I knew it right when I closed it. That cause the cat temp to take off like a rocket. I was thinking that I had a piece of wood back by the refractory shooting flames back in to the 2ndary. I could hear the afterburner sound. I wasn't sure that temp that cast iron melts at so that was my main concern(2200 if you were wondering). I don't care about replacing a cat even if I have to do it every year. I was just trying to see if I could get a 4 or so hour burn time out of my little stove so I wouldn't be doing a cold start every day.

So ultimately, as long as my flue and my cat don't exceed 2,000 degrees I should be fine. Seeing that cast melts at 2200 and stainless melts as low as 2500. The only question left is what can the refractory handle? And to be clear, I never want to see 2000 degrees on any temperature reading. Is reaching that high of a temp even possible given the set ups of these stoves?

 

[NewGuy132]

So ultimately, as long as my flue and my cat don't exceed 2,000 degrees I should be fine. Seeing that cast melts at 2200 and stainless melts as low as 2500. The only question left is what can the refractory handle? And to be clear, I never want to see 2000 degrees on any temperature reading. Is reaching that high of a temp even possible given the set ups of these stoves?

I have no idea and honestly don't want to find out. At 1800 my temp was climbing rapidly still so I opened the damper to cool it down. Now in the past I haven't had the best burn practices so I was concerned about maybe setting off a chimney fire at the same time. I was figuring that the flue gasses were 1400+ and that could easily set off any creosote. I work from home tomorrow maybe I'll run the soot eater up there to see what there is to see.

 

[Hbob]

I am going to get a battery operated catalyst thermometer as I do not have ac power near my stove. I have had great luck with Thermoworks items in our business operation and they recommend the following thermometer/probe combination for this use. Probe is rated high enough and has protected cable. I do not data log and I know I will have to turn it on to check but unless someone has a better battery operated option, I think I will try it.

We would suggest https://www.thermoworks.com/mtc/ with a Ceramic cabled probe.

https://www.thermoworks.com/wd-08467/ or probe https://www.thermoworks.com/prb-k-420/

 

[Woodsplitter67]

I am going to get a battery operated catalyst thermometer as I do not have ac power near my stove. I have had great luck with Thermoworks items in our business operation and they recommend the following thermometer/probe combination for this use. Probe is rated high enough and has protected cable. I do not data log and I know I will have to turn it on to check but unless someone has a better battery operated option, I think I will try it.

We would suggest https://www.thermoworks.com/mtc/ with a Ceramic cabled probe.

https://www.thermoworks.com/wd-08467/ or probe https://www.thermoworks.com/prb-k-420/

were using the 6 inch Ktype 2k degree thermocoupler

just as a heads up

 

[Eman85]

I am going to get a battery operated catalyst thermometer as I do not have ac power near my stove. I have had great luck with Thermoworks items in our business operation and they recommend the following thermometer/probe combination for this use. Probe is rated high enough and has protected cable. I do not data log and I know I will have to turn it on to check but unless someone has a better battery operated option, I think I will try it.

We would suggest https://www.thermoworks.com/mtc/ with a Ceramic cabled probe.

https://www.thermoworks.com/wd-08467/ or probe https://www.thermoworks.com/prb-k-420/

https://www.auberins.com/index.php?main_page=product_info&cPath=20_3&products_id=22 This is the probe most of us use. You can order it with the mini connector which will plug into most other meters.

 

[Hbob]

https://www.auberins.com/index.php?main_page=product_info&cPath=20_3&products_id=22 This is the probe most of us use. You can order it with the mini connector which will plug into most other meters.

Thank you for that link. That probe is a bit less expensive than the Thermoworks probe. I wish the Auberins meter had a battery version.

 

[arnermd]

Thanks. I tried to keep on top of it and remember everything that I did. Most likely it was all of the wood off gassing at the same time one the deep bed of hot coals. I have a 30+ft chimney so I already have plenty of draft so I'm sure that didn't help the situation. I didn't have time for a fire last night, but I'll probably be back at it either tonight or tomorrow.



Yes this was probably all of the wood off gassing at the same time due to the bed of coals. I was home so I was doing 2-3 hours reloads of 2-3 large splits so there was quite the coal bed.



Typically this is what I do when I'm just tossing in my usual 2-3 splits. This time I put in 6 or so and they stacked up to the damper flap. Also one of them fell right in front of the refractory so it was probably shooting flames back in to the 2ndary. My stove is also thermostatically controlled so aside from closing the air down there really wasn't anything I could do. I thought for a minute or two about taking some wood out and putting it in to a 5 gallon bucket of water, but that would have been a giant mess.



Opening the stove was probably the worst thing that I could do and I knew it right when I closed it. That cause the cat temp to take off like a rocket. I was thinking that I had a piece of wood back by the refractory shooting flames back in to the 2ndary. I could hear the afterburner sound. I wasn't sure that temp that cast iron melts at so that was my main concern(2200 if you were wondering). I don't care about replacing a cat even if I have to do it every year. I was just trying to see if I could get a 4 or so hour burn time out of my little stove so I wouldn't be doing a cold start every day.

2200 wow.... I think that's a record.... Was that at the cat?

 

[arnermd]

So ultimately, as long as my flue and my cat don't exceed 2,000 degrees I should be fine. Seeing that cast melts at 2200 and stainless melts as low as 2500. The only question left is what can the refractory handle? And to be clear, I never want to see 2000 degrees on any temperature reading. Is reaching that high of a temp even possible given the set ups of these stoves?

Stuff can fail long before you reach the melt temp, I would not use that as a guide....

• Remember materials age faster at higher temps and with cycling, so it is a combination of temperature, time and number of thermal cycles.
  • Below a certain temp, cycle life is infinite, but I do not know what that temp is. We need a materials expert..... @U235 Care to chime in here?
• Rate of change can also damage material. Cast iron is great at high temps but drop it in a bucket of water and it will crack in a New York minute....
• We also have to think about gaskets, hot temp cycles can compress the gaskets and eventually they will take a set and leak at cold temps.

My opinion:
2000 is really hot... anywhere. At 1700 - 1750 I would be taking action to cool it down, air full closed, plug the secondary inlet, close the key damper if you have one. Another trick is to dump ash or sand on the fire, I have done that in the past.

Since I have been logging data (2 years now) the peak temps I have ever logged are:

• Cat: 1714
• Flue gas: 1388
• Griddle: 735

I record at 2 minute data rate so there were probably some higher peaks I did not capture but they were short lived.....

 

[arnermd]

Thank you for that link. That probe is a bit less expensive than the Thermoworks probe. I wish the Auberins meter had a battery version.

This is what I use for logging.
Perfect Prime TC0520

It runs on battery, 4 TC channels, records data and has an alarm, not very loud though. It has a USB port so you could plug in one of those battery packs for longer life. or you can use AAA's.

Only bad thing about it is the LCD screen is hard to read across the room but I also have Watlow displays that I can read from my TV spot on the couch so it is of no concern to me.

 

[AsylumResident]

I have had things more under control lately. Now that I've gone through a very cold snap I understand how the stove operates a little differently in very cold temps. Right now the cats cruising around 1000 and STT at 525.

 

[Eman85]

My cat has been reading 68 for 2 days now. 0 degrees last week 65 today outside, gotta love it. Anyone need any mud?

 

[arnermd]

I have had things more under control lately. Now that I've gone through a very cold snap I understand how the stove operates a little differently in very cold temps. Right now the cats cruising around 1000 and STT at 525.

View attachment 323770

Its a good looking stove, great pic, eye candy. No warming shelves? If you get the shelves they also include mitten warmers!

 

[arnermd]

Some big picture plots just FYI....

- Most of this data is with my metal cat installed
- Couple instances I had the flue go to 1200 (highlighted in yellow)
- Cat routinely peaks over 1600, max was 1678 last night....
- On 1/23 I blocked 4 of the fireback holes with screws
- On 1/25 I removed 2 of the fireback screws, only 2 of 8 were blocked.

this is a plot of cat hot time, for each burn I calculate how log the cat was over 1000. You can see where the cold weather came in, around 1/15. I was running bigger loads and more air.

This is a plot of cat time over 1600F. Not good..... Clearly the overtemp conditions are getting worse, more frequent and longer duration. Might be a correlation with colder outside temps, maybe draft related?
- Notice the spike on 1/14 went 1.5 hours (this was one where I blocked the secondary inlet and temps hung bad, not much sleep that night)

 

[AsylumResident]

Its a good looking stove, great pic, eye candy. No warming shelves? If you get the shelves they also include mitten warmers!

I was all about the shelves. My wife said we could do this stove, as long as I didn't put the shelves on it. So I don't have shelves on it...yet.

 

[U235]

Stuff can fail long before you reach the melt temp, I would not use that as a guide....

• Remember materials age faster at higher temps and with cycling, so it is a combination of temperature, time and number of thermal cycles.
  • Below a certain temp, cycle life is infinite, but I do not know what that temp is. We need a materials expert..... @U235 Care to chime in here?
• Rate of change can also damage material. Cast iron is great at high temps but drop it in a bucket of water and it will crack in a New York minute....
• We also have to think about gaskets, hot temp cycles can compress the gaskets and eventually they will take a set and leak at cold temps.

My opinion:
2000 is really hot... anywhere. At 1700 - 1750 I would be taking action to cool it down, air full closed, plug the secondary inlet, close the key damper if you have one. Another trick is to dump ash or sand on the fire, I have done that in the past.

Since I have been logging data (2 years now) the peak temps I have ever logged are:

• Cat: 1714
• Flue gas: 1388
• Griddle: 735

I record at 2 minute data rate so there were probably some higher peaks I did not capture but they were short lived.....

I’ll definitely agree with @arnermd that reaching the melting point is not required to achieve failure in any structure (or material). If I had to guess, the failure mechanism of refractories is fatigue. Since there are no significant pressures or forces in these stoves, the primary source of stress is likely thermal. Note that if you heat something up slowly and let it expand unconstrained, it won’t experience any stress. You get thermal stresses in something when there is a gradient in temperature either in time (thermal shock) or in location (very hot facing the catalyst, cooler facing the back wall). Bringing the stoves up to temp slowly (ie not forcing flames up the secondary to jump start the catalyst), avoiding opening the stove when hot (rushing cold air over hot surfaces), and keeping catalyst temps “reasonable” (keeping temperature gradient within the refractory emgine in control) will all keep the stresses low. I’m guilty of all of these. And Sometimes managing 2 and 3 will be challenging.

Here’s an article that uses a little more engineering jargon if you’re interested. https://www.sciencedirect.com/science/article/abs/pii/S0272884220311925 My takeaway was that if the thermal shock is severe enough, the stresses are high enough (and or strength is reduced enough) failure can occur with few exposures.

 

[Woodsplitter67]

So since iv put tue metal cat in my catalyst hasn't seen 1500 degrees.. if anything my catalyst hasn't gotten above 1450 ish

The weird this was.. I ran both cats during the cold snap.. as soon as the ceramic went back in.. the SHTF.. take the ceramic out and low cat temperatures again..

I think that Iv had the most issues with my stove with a mix of ceramic cat and cold temperatures.. Going forward.. Ill be sure to have the steel cat in when the cold snaps arrive and keep it in for the duration of the cold..

 

[JohnDaileyNH]

This is my favorite weather to run this stove. Mid 30s outside. Snow coming in. Half load of wood, 50% air and just let it cruise. Cat at 1080, STT 375. House at 70°. It'll burn on a half load like this for 3-4 hours. Rinse repeat all day