2023/24 VC Temperature discussion thread

[arnermd]

This is a situation where I would love to see what would have happened if you didn't touch the air. Would it have eventually plateaued out and come down? Or just go to the moon.

Yeah.... I am always 2 steps behind this stove. Before I cut the air it was in a pretty strong uptrend so I guess it would have gone to 1400+.... But who knows.

If memory serves: I too have seen really high cat temps with a small load, but it was caused by burning wood right at the secondary inlet channeling flame up into the refractory. As best I recall... I went in and moved the wood towards the front and the cat temps came right down and stayed down. Unfortunately I can not move wood around with a full load burn....

And.... you specifically said "big splits", they can give you a lot of smoke with a small fire, just not a lot of surface area for combustion and big splits will have more moisture as they take longer to dry. I have definitely seen this too. When I plan on doing a small fire I use smaller splits, I save the big ones for full load overnight burns and I put them in the middle/ top of the load, not the bottom, unless there is a very healthy bed of coals to keep the momentum up.

I have thought about modifying my secondary inlet to create another "turn". A carefully crafted sheet metal piece to pull gas from the top of the box and bring it down to the secondary inlet. Would take away from the wood load and small fires would probably be really hard to get up to temp....

Regarding your burn last night: My first thought is you had too much primary air and it was giving you complete combustion and diluting the exhaust temps. But I could be wrong....

Very curious to see what kind of draft readings you get when cruising with a full load. Keep the data coming!

 

[gthomas785]

With the short stack is your setup prone to back puffing?

So yes I do get backpuffing sometimes. My observations tell me that it may have a little bit to do with draft, but not really. The backpuffing behavior happens if there's a lot of heat in the box and it's really starved for oxygen. The fire goes into a cycle where smoke will build up in concentration until it hits the LEL and then explodes. I suppose stronger draft could help to draw more smoke out of the firebox but without primary air entering, the smoke concentration will still build up.
I don't really know how to stop it except by giving the fire more air, but then heats everything up even more. Since it doesn't usually last too long and my house is drafty enough that the smoke smell doesn't build up too much, I tend just to wait it out and it stops.

 

[arnermd]

So yes I do get backpuffing sometimes. My observations tell me that it may have a little bit to do with draft, but not really. The backpuffing behavior happens if there's a lot of heat in the box and it's really starved for oxygen. The fire goes into a cycle where smoke will build up in concentration until it hits the LEL and then explodes. I suppose stronger draft could help to draw more smoke out of the firebox but without primary air entering, the smoke concentration will still build up.
I don't really know how to stop it except by giving the fire more air, but then heats everything up even more. Since it doesn't usually last too long and my house is drafty enough that the smoke smell doesn't build up too much, I tend just to wait it out and it stops.

yeah that was my thinking as well.... not so much draft related, just starved for air.

 

[Woodsplitter67]

I didn't do a very large load but I was hoping to get the cat cruising north of 1000, which is typical, to see what the draft would be. My stove wasn't interested in getting there last night.

I was just asking because sometimes we get caught up in what we think is normal..

Just as a general guideline .. having different cat temperatures are normal.. Im happy with a temperature range of 800 to 1475.. as long as no smoke is visible.. I try to keep the catalyst temperature down

 

[Woodsplitter67]

yeah that was my thinking as well.... not so much draft related, just starved for air.

I feel its a combination.. starved for air and a buildup of gasses in the box.. you finally get an ignition and off it goes..

 

[AsylumResident]

I was just asking because sometimes we get caught up in what we think is normal..

Just as a general guideline .. having different cat temperatures are normal.. Im happy with a temperature range of 800 to 1475.. as long as no smoke is visible.. I try to keep the catalyst temperature down

I understand. So far I see no smoke north of 1,100 for cat temp as the temp builds. On the way back down I don't see smoke again until about 850 cat temp.

 

[arnermd]

I was just asking because sometimes we get caught up in what we think is normal..

Just as a general guideline .. having different cat temperatures are normal.. Im happy with a temperature range of 800 to 1475.. as long as no smoke is visible.. I try to keep the catalyst temperature down

I want to say there are different levels of combustion for the cat.... It feels like over 550 some compounds in the smoke are combusting but there is another level over 850 where more (maybe more complex) compounds are combusting....

Thinking it is like a petroleum analogy.... like the lighter hydrocarbons ignite first and then eventually the heavier ones.

I don't know, just theorizing.... I could be full of 💩....

 

[Woodsplitter67]

I want to say there are different levels of combustion for the cat.... It feels like over 550 some compounds in the smoke are combusting but there is another level over 850 where more (maybe more complex) compounds are combusting....

Thinking it is like a petroleum analogy.... like the lighter hydrocarbons ignite first and then eventually the heavier ones.

I don't know, just theorizing.... I could be full of 💩....

I think you are correct.. the lower like 550/600 your right.. I dont think that 850 much if anything is slipping by.. I think sometimes people get caught up on the number a little. That say normally my cat runs at 1200 but if someone sees it at 875 they feel that the stoves not running correctly.

I say this because I have had a number of people PM me and ask about different cat temperatures. This has gone on for the past 3 years.. Just for clarity Im not complaining and its ok to do so for those who read this.

I like to burn low.. really low .. like during shoulder season .. I burned with STT of 350 last weekend for most of the day last Saturday trying to keep the catalyst below 1000

I know its burning clean at the lower temperatures because there none of the higher stages of creosote forming in the upper part of the stovepipe..

 

[arnermd]

I gave the metal cat a vinegar bath. I did not boil it, just soaked it in hot white vinegar for 30 minutes, rinsed with distilled water.

Seems to have worked. Had some nice burns Sat and Sun. During the day I did some small fires, 3-4 small/med splits. Just to keep the coal bed going....

In the evening I raked coals to the back, loaded up (3/4 load) and let er go... 50% air. Looks pretty good to me.

So.... metal cat has at least 2 lives we shall see how long it lasts.

The metal cat seems less "edgy" to me, it seems harder to get it up over 1000, but peak temps are less. Like a ceramic on Xanax....

 

[Woodsplitter67]

I gave the metal cat a vinegar bath. I did not boil it, just soaked it in hot white vinegar for 30 minutes, rinsed with distilled water.

Seems to have worked. Had some nice burns Sat and Sun. During the day I did some small fires, 3-4 small/med splits. Just to keep the coal bed going....

In the evening I raked coals to the back, loaded up (3/4 load) and let er go... 50% air. Looks pretty good to me.

So.... metal cat has at least 2 lives we shall see how long it lasts.

The metal cat seems less "edgy" to me, it seems harder to get it up over 1000, but peak temps are less. Like a ceramic on Xanax....

View attachment 319031

I do like the steel over the ceramic.. Me personally I feel it lights off faster in my stove and certainly doesn't get as hot.. I really like that its all metal, as I broke a ceramic when cleaning the stove. Im pretty sure the highest peak on my metal cat was something like 1480

 

[AsylumResident]

This is my burn from last night. This burn is pretty much how all my burns went through the weekend.
- I rake the coals more towards the back
- Load it about 3/4 full with mostly ash
- Once flue temp hits 650, maybe to 700, close the bypass.
- 100% air until the cat temps reach 950 to 1000 then close air to 50%.
(I did play a little bit with air at 60% versus air at 40%. I get higher cat peaks with the air at 40% (1600+) with a slightly longer burn than at 60% with cat peaks just about 1500 and somewhat shorter burns, exactly what I would expect . Now I'm just playing with slight variations to see what happens.)



I also measured draft periodically throughout the weekend. What I found is that my draft is typically .08 to .1 pretty consistently with flue temps under 700. With a flue temp of 715 the draft read 0.11 and with a flue temp of 780 the draft read .115.

 

[arnermd]

Very interesting burn this morning.... I took vacation this week so I have plenty of time to sit and tinker with the stove

• A few coals left from overnight burn, raked them to back.
• 3 med ash splits, <1/2 a load
• Damper open, full air, let the load catch for a bit.
• At 650 on the flue gas: engaged the cat, popped off and climbed.
• At 1000 on the cat I started nudging air down, I did this in very small steps, maybe 5 "nudges" in 20 min down to ~ 30% air
• Flames died away, orange glow only and occasionally I would get an "aurora" (a slow moving flame that spreads through the firebox then goes out)
• Thought I had a real good burn going and then the gentle aurora turned more violent and I was getting back puffing of smoke from the griddle.
• I closed my key damper to kill the draft and all seemed better for a 1 0minutes but then I started getting backpuffs coming from the secondary air inlet.
• Opened the key damper and eventually got backpuffs from the griddle again.
• Started closing down the key damper gradually and I was able to find a happy medium where no back puffing was occurring, but still getting gentle auroras. Draft measured at this point was 0.08-0.09 iwc.

The plots below are 2 second data, so you can see where the ignition events were occurring, you can see it in cat temps and flue temps as noise....

Interesting the correlation between where the smoke was coming out vs draft level.
- Low draft smoke comes out the secondary inlet and rises from behind the stove
- High draft and the smoke comes from the griddle gasket.

 

[AsylumResident]

Very interesting burn this morning.... I took vacation this week so I have plenty of time to sit and tinker with the stove

• A few coals left from overnight burn, raked them to back.
• 3 med ash splits, <1/2 a load
• Damper open, full air, let the load catch for a bit.
• At 650 on the flue gas: engaged the cat, popped off and climbed.
• At 1000 on the cat I started nudging air down, I did this in very small steps, maybe 5 "nudges" in 20 min down to ~ 30% air
• Flames died away, orange glow only and occasionally I would get an "aurora" (a slow moving flame that spreads through the firebox then goes out)
• Thought I had a real good burn going and then the gentle aurora turned more violent and I was getting back puffing of smoke from the griddle.
• I closed my key damper to kill the draft and all seemed better for a 1 0minutes but then I started getting backpuffs coming from the secondary air inlet.
• Opened the key damper and eventually got backpuffs from the griddle again.
• Started closing down the key damper gradually and I was able to find a happy medium where no back puffing was occurring, but still getting gentle auroras. Draft measured at this point was 0.08-0.09 iwc.

The plots below are 2 second data, so you can see where the ignition events were occurring, you can see it in cat temps and flue temps as noise....

Interesting the correlation between where the smoke was coming out vs draft level.
- Low draft smoke comes out the secondary inlet and rises from behind the stove
- High draft and the smoke comes from the griddle gasket.

View attachment 319051

Why is is back puffing? I have yet to have a back puff that I am aware of.

 

[arnermd]

Why is is back puffing? I have yet to have a back puff that I am aware of.

Why ask why....

Back puffing occurs with low air settings where there is not enough oxygen to maintain a constant burn. So the combustion turns into a batch process, flammable gasses build up in the firebox until enough oxygen is present and then it ignites all the gasses at once, repeat....

Not clear to me why sometimes I get aurora / flash burns (very pretty with no smoke expelled) vs backpuffing (whoosh with smoke expelled). I believe they are the same phenomenon just one is more extreme than the other.

You may not have seen it yet because you are running with 50% air. I rarely experience it with air settings over 50%.

Quote of the day:
There are those that have experienced back puffing and those who will.... by me!

 

[AsylumResident]

Why ask why....

Back puffing occurs with low air settings where there is not enough oxygen to maintain a constant burn. So the combustion turns into a batch process, flammable gasses build up in the firebox until enough oxygen is present and then it ignites all the gasses at once, repeat....

Not clear to me why sometimes I get aurora / flash burns (very pretty with no smoke expelled) vs backpuffing (whoosh with smoke expelled). I believe they are the same phenomenon just one is more extreme than the other.

You may not have seen it yet because you are running with 50% air. I rarely experience it with air settings over 50%.

Quote of the day:
There are those that have experienced back puffing and those who will.... by me!

I've seen the aurora plenty of times, as you explained, when I turn the air down. I also have it happen when my cat gets above 1600. All of a sudden it starts aurora(ing) causing the cat temp to drop but I have not had it extreme enough to actually whoosh and back puff yet. Back in October when I was regularly turning the air from 100% to 10% I still never got the back puff.

 

[sargeott]

Very interesting burn this morning.... I took vacation this week so I have plenty of time to sit and tinker with the stove

• A few coals left from overnight burn, raked them to back.
• 3 med ash splits, <1/2 a load
• Damper open, full air, let the load catch for a bit.
• At 650 on the flue gas: engaged the cat, popped off and climbed.
• At 1000 on the cat I started nudging air down, I did this in very small steps, maybe 5 "nudges" in 20 min down to ~ 30% air
• Flames died away, orange glow only and occasionally I would get an "aurora" (a slow moving flame that spreads through the firebox then goes out)
• Thought I had a real good burn going and then the gentle aurora turned more violent and I was getting back puffing of smoke from the griddle.
• I closed my key damper to kill the draft and all seemed better for a 1 0minutes but then I started getting backpuffs coming from the secondary air inlet.
• Opened the key damper and eventually got backpuffs from the griddle again.
• Started closing down the key damper gradually and I was able to find a happy medium where no back puffing was occurring, but still getting gentle auroras. Draft measured at this point was 0.08-0.09 iwc.

The plots below are 2 second data, so you can see where the ignition events were occurring, you can see it in cat temps and flue temps as noise....

Interesting the correlation between where the smoke was coming out vs draft level.
- Low draft smoke comes out the secondary inlet and rises from behind the stove
- High draft and the smoke comes from the griddle gasket.

View attachment 319051

This is great data. Keep it up man. It's good stuff.

 

[DullAxe]

Burned some of my dry wood tonight instead of the NIELs logs, to have a change from the relatively mundane world of pressed sawdust.
I started the fire about an hour before dinner and added a bit over half a stove's worth of wood after the initial coals formed. That burned down over about 3.5 hours or so as I had turned the air down to a little under 50%. I did a smaller reload about 30 minutes ago on top of a large bed of coals that I had redistributed. The catalyst temp reached 1494 with the air at only 50% and it was still climbing slowly. Auroras (good name for those, by the way) rolling, subsiding, and reforming driving the temperature higher with each outburst. At that point I didn't really want to venture into higher temperatures so I opened the air to around 70% or so and temps started dropping again. It's been around 20 minutes and the cat has leveled out to around 1150.

 

[AsylumResident]

Burned some of my dry wood tonight instead of the NIELs logs, to have a change from the relatively mundane world of pressed sawdust.
I started the fire about an hour before dinner and added a bit over half a stove's worth of wood after the initial coals formed. That burned down over about 3.5 hours or so as I had turned the air down to a little under 50%. I did a smaller reload about 30 minutes ago on top of a large bed of coals that I had redistributed. The catalyst temp reached 1494 with the air at only 50% and it was still climbing slowly. Auroras (good name for those, by the way) rolling, subsiding, and reforming driving the temperature higher with each outburst. At that point I didn't really want to venture into higher temperatures so I opened the air to around 70% or so and temps started dropping again. It's been around 20 minutes and the cat has leveled out to around 1150.

That's interesting about the auroras. When my cat gets high and those start firing off, it starts lowering my cat. I'm assuming it's burning off excess smoke and gasses built up towards the top of the firebox, reducing fuel for the cat. But yours was increasing the temperature.

Most of my burns will go north of 1400 for a short period of time and they don't typically 'level' off. I know others discuss their stove as peaking and then leveling off but mine is pretty consistently more of bell curve that gets up to temp quick and then slowly drops off the back end.

 

[AsylumResident]

This burn surprised me. I did everything the same as I have the past few days but for whatever reason the cat barely broke 1000 (which is fine, just not typical) and this was the longest burn I have had to date. 10 hours later and there was a decent coal bed to work with. Air stayed at 50% for the entire burn. I would be ok with this kind of burn, just would like to see the STT a little higher; there were some pretty low dips in there.

 

[arnermd]

Burned some of my dry wood tonight instead of the NIELs logs, to have a change from the relatively mundane world of pressed sawdust.
I started the fire about an hour before dinner and added a bit over half a stove's worth of wood after the initial coals formed. That burned down over about 3.5 hours or so as I had turned the air down to a little under 50%. I did a smaller reload about 30 minutes ago on top of a large bed of coals that I had redistributed. The catalyst temp reached 1494 with the air at only 50% and it was still climbing slowly. Auroras (good name for those, by the way) rolling, subsiding, and reforming driving the temperature higher with each outburst. At that point I didn't really want to venture into higher temperatures so I opened the air to around 70% or so and temps started dropping again. It's been around 20 minutes and the cat has leveled out to around 1150.

Pretty similar experience to what I have been seeing.... Stove seems to run a lot different under 50% air. Sounds like you had a thick bed of coals, that may have been what was driving the cat up.

I have been experimenting with smaller loads (1/2 or less) on a small/moderate bed of coals, letting the load catch before engaging the cat and then nudging air down to 20 - 30%. Cat temps at reload are 500 - 600. The cat recovers to 1000 - 1200 pretty quickly and the burns seem to be going really well, I get the aurora's going with generally stable cat temps. But an hour or two later I start with the backpuffing and I have to increase air over 50%..... The other day I was able to find a balance with draft where it stopped backpuffing but I have not been able to duplicate that.

 

[arnermd]

This burn surprised me. I did everything the same as I have the past few days but for whatever reason the cat barely broke 1000 (which is fine, just not typical) and this was the longest burn I have had to date. 10 hours later and there was a decent coal bed to work with. Air stayed at 50% for the entire burn. I would be ok with this kind of burn, just would like to see the STT a little higher; there were some pretty low dips in there.

View attachment 319125

yeah that's a weird one.... It happens.

What are you using to measure STT? I know you have a TC but what kind? I am finding it hard to get a good STT reading, I am using a magnetic disk with a TC in the middle and it is reading low unless I insulate around it...

Looks like this.....

 

[AsylumResident]

I have this one from Auber. It reads, and has read, about 30 degrees cooler than IR gun. But, what is the margin of error for the IR gun?

 

[arnermd]

Yeah that's a better design, spring loaded. Difference is in the price.... mine was like $10, Auber is $60....

I may just make my own, I got some TC wire and magnets....

 

[DullAxe]

That's interesting about the auroras. When my cat gets high and those start firing off, it starts lowering my cat. I'm assuming it's burning off excess smoke and gasses built up towards the top of the firebox, reducing fuel for the cat. But yours was increasing the temperature.

Most of my burns will go north of 1400 for a short period of time and they don't typically 'level' off. I know others discuss their stove as peaking and then leveling off but mine is pretty consistently more of bell curve that gets up to temp quick and then slowly drops off the back end.

When the auroras were occurring during that burn the cat temp would increase slightly overall, the aurora would occur and the cat temp would fall slightly, and repeat the cycle. The cat temps after the aurora dips were higher than the previous incident - so an overall increasing trend.

 

[GrumpyDad]

I have this one from Auber. It reads, and has read, about 30 degrees cooler than IR gun. But, what is the margin of error for the IR gun?

View attachment 319131View attachment 319131

the cheap IR guns from amazon can be fairly accurate but depending on the surface some can be outright just so wrong it's incredible. Most of the time though people just dont know how to use them, and all IR guns have challenges w/ shiny objects to some degree. There's a distance to the surface that every thermometer should publish and you need to adhere to that, even if you see very little difference between 12" and 60" on a stove pipe, on other materials and temperatures it could be grossly inaccurate so for the best reading, read your manual and follow what it says.
I have a fluke, and they have a published page that shows you how to get the best results:

How to Get Great Results with an Infrared Thermometer

Infrared (IR) thermometers enable you to measure temperature quickly, at a distance, and without touching the object you're measuring. They are so useful, easy, and even fun to use that they have become as common in kitchens as they have on factory floors. Infrared thermometers are often used to...

www.fluke.com