2023/24 VC Temperature discussion thread

[AsylumResident]

Center of the griddle, closer to the back ~2" in front of the griddle hinge

My griddle reads ~30-50 deg low, as compared to an IR gun and a magnetic dial.

That makes sense, it looked weird that the temps were that low. I had to move my magnetic end from the griddle to the the black cast just behind the griddle because the temperature sensor would shift every time I opened and close the griddle. This would give me ridiculous temp readings and error readings. So I moved it to the just behind the griddle to keep it stationary which lead to relearning the right stove temps in a new area. I found that the readings are about 50 degrees lower in this position than on the griddle.

 

[AsylumResident]

I have been running differently than @arnermd lately. I have been running hotter up front for longer, letting things catch more than I have normally and turning the primary air lever to about 75% once I hit 1100 cat and leaving it there for about an hour and a half.


At about an hour and a half I turned the air down to close to 10% for the rest of the night. My temps don't stay as high as long as yours but this was a little more than a half load of locust and I had a nice bed of coals at 5:30am this morning. The cat peaked at 1364. Unfortunately my system only tracks two temps so my flue isn't on the graph. The flue temp hung around 700 for the higher cat times on the graph.

 

[Ashful]

DAQ:

• Perfect Prime TC0520: Amazon Link
  • Data is exported as a .csv file and I do plots and archiving in excel.
• Flue gas temp: 1/8" type K insertion probe, ~14" above the stove top
• Cat Temps: 1/16" type K insertion probe. Inserted in the factory provided hole. Tip is 1" below the cat in the center.
• Griddle: Magnetic type K, center of griddle 2" in front of griddle hinge line. Link here

Very cool. I had a similar rig on my old Jotul F12 downdraft cat stoves, but never bothered replicating the same on the BK's, as they're just so predictable that I never saw the need. I do miss the data collection side of things, though.
https://www.aliexpress.us/item/3256...b79297&afSmartRedirect=y&gatewayAdapt=glo2usa

That spike at the very end of the secondary burn (@01:40) is very typical of my burns. It is very normal to see that to varying degrees. I believe it has something to do with the state of the coals / fuel. I am not and expert in wood combustion phases....

I'm not a combustion expert either, but I suspect that big spike at 1:40 immediately followed a collapse of the wood load. You know, the logs on the bottom had been consumed far enough for the stack to lose structural integrity, upper logs collapse into the hole, and either just rearrange airflow through the stove or expose a bunch of surface that was previously out of the air path.

Maybe the last of the wood chunks are coming apart and that exposes more surface area for combustion just before the coaling stage? That might explain the oscillations, multiple chunks broke apart at different times?

I believe the dithering from 1:40 - 2:40 is just the normal behavior of your thermostat, nothing to do with what's happening with the fuel. Every thermostat must have some hysteresis to avoid oscillation, and I think that's what you're seeing there.

 

[arnermd]

I have been running differently than @arnermd lately. I have been running hotter up front for longer, letting things catch more than I have normally and turning the primary air lever to about 75% once I hit 1100 cat and leaving it there for about an hour and a half.

View attachment 320590
At about an hour and a half I turned the air down to close to 10% for the rest of the night. My temps don't stay as high as long as yours but this was a little more than a half load of locust and I had a nice bed of coals at 5:30am this morning. The cat peaked at 1364. Unfortunately my system only tracks two temps so my flue isn't on the graph. The flue temp hung around 700 for the higher cat times on the graph.

I think smaller loads also keep the peak temps down..... I am trying smaller loads during to day. I seem to have better luck.

 

[sargeott]

@arnermd
I still would like to see your data when you do a burn with bark removed from your wood. Here is my logical reasoning:
Bark is harder (on most species) to light and burn. I know there are exceptions, so if you do this test please mention what type of wood your burn is on. Bark will also require a higher combustion temperature to burn and makes lots of smoke.
this could be why you are see late spikes in cat temps over time.
Or, its the wood in the middle of your stove/top of stove that is baking as the lower logs burn and by the time the higher up logs ignight, they off gas later in your burn cycle.
My experience in testing:
I would load a hot box of pine/white oak mix with pine lower in the box and oak higher up. My logic: the pine with ignight, turn into coals and the oak will slow cook for my longer burn cycles.
My smoke out the stack is minimal on these. Then I have tried throwing some bark only chunks on the very top and that bark stays unburned for a few hours. It won't ignight or burn until the oak burns down and then BOOM the bark will catch and dump tons of smoke into the fire box and overwhelms my cat. When this happens I get lots of smoke out of the chimney even when all my temps are nice and hot.
I think bark is the key in cat temp issues.
Thoughts?

 

[arnermd]

Very cool. I had a similar rig on my old Jotul F12 downdraft cat stoves, but never bothered replicating the same on the BK's, as they're just so predictable that I never saw the need. I do miss the data collection side of things, though.

Yeah I would never invest the time and money to tracking data if the stove burned consistently..... My next stove will likely be a BK, but there are features of the VC I will miss.... Mainly the cook top.

but I suspect that big spike at 1:40 immediately followed a collapse of the wood load.

Certainly could be.... seems like a logical explanation. I almost always see a spike at the very end.

I believe the dithering from 1:40 - 2:40 is just the normal behavior of your thermostat, nothing to do with what's happening with the fuel. Every thermostat must have some hysteresis to avoid oscillation, and I think that's what you're seeing there.

I do not think so..... The thermostat really does not have a lot of control over the secondary temps.... they kind of do what they do. But I could be wrong.

 

[arnermd]

@arnermd
I still would like to see your data when you do a burn with bark removed from your wood. Here is my logical reasoning:
Bark is harder (on most species) to light and burn. I know there are exceptions, so if you do this test please mention what type of wood your burn is on. Bark will also require a higher combustion temperature to burn and makes lots of smoke.
this could be why you are see late spikes in cat temps over time.
Or, its the wood in the middle of your stove/top of stove that is baking as the lower logs burn and by the time the higher up logs ignight, they off gas later in your burn cycle.
My experience in testing:
I would load a hot box of pine/white oak mix with pine lower in the box and oak higher up. My logic: the pine with ignight, turn into coals and the oak will slow cook for my longer burn cycles.
My smoke out the stack is minimal on these. Then I have tried throwing some bark only chunks on the very top and that bark stays unburned for a few hours. It won't ignight or burn until the oak burns down and then BOOM the bark will catch and dump tons of smoke into the fire box and overwhelms my cat. When this happens I get lots of smoke out of the chimney even when all my temps are nice and hot.
I think bark is the key in cat temp issues.
Thoughts?

My gut is telling me this is not the cause of my issue.... but I have not tried it yet so I can't say for certain. I need to give it a try.
Wood I have been burning this year is all Ash and Oak. A lot of the ash was standing dead so it has minimal bark on it anyway. But the oak does.

I agree with you that bark creates a lot of smoke.... I have seen it too. I always thought it smokes because the bark smothers the fire and does not allow enough airflow for good combustion. But maybe that's only part of the reason.

 

[Ashful]

My next stove will likely be a BK, but there are features of the VC I will miss.... Mainly the cook top.

I can't speak to any of the other BK models, I didn't really like their cosmetics enough to really give them serious consideration, but the Ashford 30 has a lift-off cast iron top that exposes the hot top of the steel firebox below. Perfect for occasional emergency cooking during a power outage, but not super-convenient for daily use. You just lift the probe thermometer out of its hole, and then the top lifts right off. Not very heavy, it's function is mostly creating a nice convective jacket between firebox and outer stove body.

 

[Eman85]

Yeah I would never invest the time and money to tracking data if the stove burned consistently..... My next stove will likely be a BK, but there are features of the VC I will miss.... Mainly the cook top.

I can't help but agree with you. The glass front, the ash pan and the top load are the greatest things about the VC stove. We don't cook on the cook top much but it's nice.

 

[Ashful]

I can't help but agree with you. The glass front, the ash pan and the top load are the greatest things about the VC stove. We don't cook on the cook top much but it's nice.

I had three top load stoves before the current pair, and thought I would really miss it. In fact, I was holding top load up as a "must have" feature, when I was shopping for new stoves back in 2014.

However, now that I've run two stoves without topload the last several years, I'm glad I ditched it. It's another source of likely leaks, and almost eliminates the possibility of more efficient north-south loading. I wouldn't have believed you prior to 2015, if you told me I'd reverse opinion on this, but today I am so glad I got rid of the top load feature.

I can see where a cooktop would be desirable. We never cook on our stoves, even though we could, but I can understand why others would want and actually that feature, esp. if stove is installed in a kitchen.

 

[arnermd]

I had three top load stoves before the current pair, and thought I would really miss it. In fact, I was holding top load up as a "must have" feature, when I was shopping for new stoves back in 2014.

However, now that I've run two stoves without topload the last several years, I'm glad I ditched it. It's another source of likely leaks, and almost eliminates the possibility of more efficient north-south loading. I wouldn't have believed you prior to 2015, if you told me I'd reverse opinion on this, but today I am so glad I got rid of the top load feature.

I can see where a cooktop would be desirable. We never cook on our stoves, even though we could, but I can understand why others would want and actually that feature, esp. if stove is installed in a kitchen.

My Dad had an old Defiant, no cat and no glass doors. It had a side load door. That was really handy. I like the top load but often wonder if it is the best way.... I do find it difficult to get large 20" splits in at the top, I have learned over the years to save my shorter lengths for the top row. Real exciting wedging that last one in, realizing it wont fit and then can't get it back out with flames and sparks coming out the griddle at you... I got some elbow length welding gloves from Amazon, maybe this spring I will have hair on my arms and fewer burns on the forearms.

I had it wedged so bad one time I had to open the glass doors, take one out of the middle to get the last one in.... that one went out in the back yard on fire.

We don't cook the usual daily meals on the wood stove, temp is too erratic. But it is great for soups, sources, beans, jerky, dried fruit.... stuff I want to simmer all day.

Do you have an ash pan on your BK? If not do you miss it?

 

[Ashful]

Real exciting wedging that last one in, realizing it wont fit and then can't get it back out with flames and sparks coming out the griddle at you... I got some elbow length welding gloves from Amazon, maybe this spring I will have hair on my arms and fewer burns on the forearms.

lol... yeah, been there and done that, many times! I had the Jotul F12's with the top load doors for several years. Very convenient, and also a very easy way to get yourself in trouble. The worst incident was when a split of hickory or elm, both always a little gnarly with splintered faces, caught the gasket on the way thru the hole. So, there I am with the gasket falling off the top load door opening, flames licking out at me, and no good way to really seal the damn thing back up tight for a controlled burn. Glad I got rid of those stoves, just remembering that.

Do you have an ash pan on your BK? If not do you miss it?

My BK's have nice deep ash pans, with a nice heavy handle. Really nice setup. I don't know if all models have this, but at least the Ashford 30 has an ash pan standard, with a removeable 4" square plug in the middle of the floor for scraping ash into the pan. I pull the plug, drop a little round cast iron drain grate in its place, and rake the ash and coals over that. Ash falls thru into the pan and coals stay in the stove. Wonderful system, even though I had to source the drain grate myself.

 

[Eman85]

I guess we've all had our top load events with jammed pieces, burning embers popping out while loading and tearing the gasket. I guess top load wouldn't be a deal breaker. I have had front load and side load stoves in the past.

Just to keep with the topic of this thread I copied my temps from my other thread comparing with cat to without engaging cat.



Didn't want anyone calling the EPA on me so I flipped the damper and engaged my cat this evening.
Just for comparison with the cat my STT 425 Flue 475 and cat at 1320
From a previous burn with no cat - "Right now without the cat in STT is about 150* higher than the flue temp, right now 550STT flue therm 400. "

Thermometers in the same exact spots for both burns.

 

[begreen]

Not very heavy, it's function is mostly creating a nice convective jacket between firebox and outer stove body.

Not exactly lightweight either and it is big so one needs a place to set it down. IIRC it's about 40 pounds.

 

[Ashful]

Not exactly lightweight either and it is big so one needs a place to set it down. IIRC it's about 40 pounds.

It is indeed a big platter, but I'd be real surprised if it's that heavy. Always felt pretty light to me, but I only remove it once per year for the big annual cleaning. Next time one of the Ashfords is cold, I'll pull the top to get a weight.

The bigger issue than weight is that it's probably already hot or warm when the power goes out and you decide it's time to use the thing. So, you're talking oven mitts at the least, and then careful where you set it.

Like I said, a great option for the odd emergency, but not what you'd want to be using for daily cooking, if that's your goal.

 

[Dobish]

just wanted to pop in and say hello! I have been enjoying some more consistent temps this year since I added 4ft to my encore. When I first installed it, I went with just the bare minimum flue length (~13ft) but prior to burning this year I added in another 4ft section. It is amazing how much more draft I get, and how much more air control I have. I never used to be able to cut my air more than 1/2 way unless the stove was really hot, but now, even on a load of mixed punky stuff I can turn it down. Temps have been hovering around 1000-1400 on the cat, which never happened unless the stove was full of locust.
I did have an error with my AT100 but it turns out the wire had wiggled loose. My heart stopped when the alarm went off unexpectedly!

 

[arnermd]

This kind of stuff drives me crazy..... Below are 2 plots from the past 2 overnight burns, very different results.

• Stove was cold on both burns, started a small fire, 2-3 med splits
• Engaged the cat when griddle was > 450 - 500
• Waited for cat to peak, then loaded a full load on top of a very healthy, hot bed of coals.
• Imeadiately engaged the cat, waited for ~1000F on the cat and then dialed air down
• Went to bed.

First night: Air set to ~60%, Cat temps climbed up to 1550, not much wood left in the morning but a bed of coals. Glass was clean. Seemed like a good burn but the peak temps were a bit higher then I want to see.

Second night: Essentially the same process as the first but set air to 40% for the overnight. Cat temps crashed, woke to a half full box of charred wood and glass was black. Opened up the air and burned it all down for 3 hours..... total disaster.

 

[Eman85]

I've been burning with the cat since it turned colder here and find it much easier to control the cat with less than a full load. Half a box is real easy and 3/4 works good just have to plan the loading in time so I can go to bed. Still wake to a good bed of coals with 3/4 box
@arnermd I never saw you comment on my thread about burning without the cat. I look at your graphs and compare to my burns and one thing I notice is there is a lot of "dirty burn" time where the cat falls below 600*. Just from my experiments with burning without the cat it seems the only gain is the clean burn time when the cat is hot. I debate whether it's worth the worry some days to fool with the cat.

 

[arnermd]

I've been burning with the cat since it turned colder here and find it much easier to control the cat with less than a full load. Half a box is real easy and 3/4 works good just have to plan the loading in time so I can go to bed. Still wake to a good bed of coals with 3/4 box
@arnermd I never saw you comment on my thread about burning without the cat. I look at your graphs and compare to my burns and one thing I notice is there is a lot of "dirty burn" time where the cat falls below 600*. Just from my experiments with burning without the cat it seems the only gain is the clean burn time when the cat is hot. I debate whether it's worth the worry some days to fool with the cat.

I saw your last post about burning with the cat, to be honest I did not understand what you were saying..... sorry.

What differences are you seeing in your temps vs my plots?

Dirty burn time: I think when the cat falls off at the end of burn there is no more smoke to combust it is just coals which burn clean so no fuel for the cat. I could be wrong about that.....

Half loads: I think most of us have found partial loads are easier to control. That has been my experience for sure. It is still not 100% controllable for me, but better.

Cat: In my opinion the greatest benefit of the cat is achieving low air, long duration clean burns. Certainly we get some extra heat out of the cat but I think it is marginal. If you are running with moderate to high air flows then I think the cat is of marginal benefit and makes a small improvement in heat output and cleanliness.... all just my opinion.

I think I recall somebody advocating running with the bypass open (not sure if that was you or not) To me that is crazy and a massive waste of energy. Running with the damper open on my stove sends heat and flame right up the stack, maybe it is different on other models. The 2n1 stoves are meant to achieve secondary combustion even without the cat. Even the old non cat VC stoves were designed to have secondary burns for extra heat and cleaner burns. Running with the damper open defeats the entire secondary burn and heat exchange area.

Again.... all just my opinion and my experience with my stove.

 

[Rusty18]

This kind of stuff drives me crazy..... Below are 2 plots from the past 2 overnight burns, very different results.

• Stove was cold on both burns, started a small fire, 2-3 med splits
• Engaged the cat when griddle was > 450 - 500
• Waited for cat to peak, then loaded a full load on top of a very healthy, hot bed of coals.
• Imeadiately engaged the cat, waited for ~1000F on the cat and then dialed air down
• Went to bed.

First night: Air set to ~60%, Cat temps climbed up to 1550, not much wood left in the morning but a bed of coals. Glass was clean. Seemed like a good burn but the peak temps were a bit higher then I want to see.

Second night: Essentially the same process as the first but set air to 40% for the overnight. Cat temps crashed, woke to a half full box of charred wood and glass was black. Opened up the air and burned it all down for 3 hours..... total disaster.


View attachment 321070

View attachment 321073

Off the bat it looks like the first burn was 20 mins in before turn down. Second burn was only 10 mins in.

 

[arnermd]

More weirdness last night.....

• Did my usual small preburn to get a hot bed of coals and heat the cat up.
• When cat started to roll over I added a full load on top and engaged the cat after a few minutes.
  • Yes the cat was still pretty hot (1000F), but I wanted to go to bed....
• Woke up an hour later to cat alarming at 1600 and stove temps very high
  • Griddle was over 650, flue at 850, firebox was a very intense orange glow and lots of flame.
• Nudged the air down to 45% and saw temps starting to drop, went back to bed.
• Woke up in the morning to clean glass and a meager bed of coals. Burned seemed clean.

Confusing thing: Why would adjusting the prmary air, just a little, cause the whole burn to crash? There was plenty of wood in the firebox at the time.

• Maybe the primary burn was so clean there was no smoke for the cat? Seems unlikely.
• Maybe the cat is dead and I am only getting secondary burning with a vigoruous primary burn?

Switched back to my ceramic cat this morning to see if that makes a difference.

 

[U235]

@arnermd - man. What a hassle. 60 or 50% and it goes nuclear 45 or 40% and it slowly decays to nothing. Assuming these last couple graphs all have similar outside temps and same flue damper setting, IE similar draft for a given flue temp. it’s really tough to think what might be the issue.

I had two possible things to try, one was to close the damper based on flue temperature and not stove top temp… I almost exclusively cold start. With my setup, I can almost always get a good cat light off with a griddle temp <250 as long as I have the right flue temp-outside temp delta. This ensures that most of the initial off-gassing/catalyst warmup is dumped into heating up the cast iron. Note. This gives controlled catalyst light off, but produces minimal room heat.

The second suggestion was something we’ve discussed outside the group, but wood placement seems to have a huge effect in my encore. I wonder if you put something in the firebox to force there to maintain a gap between the wood and back wall. Maybe a rectangle of 1” steel. Then maybe you can leave the air at higher setting so it doesn’t crash and avoid having wood shift later in the burn and fall against the back wall. Would certainly want to pick something that isn’t going to pollute your catalyst and size it so that it can’t fall and break your glass. If there is always a gap such that smoke isn’t directly entering the engine, that should help your catalyst temp excursions.

Or maybe your metal cat is dead and you’ll be good tonight. Who knows?

Edit: prototype attached.

 

[arnermd]

@arnermd - man. What a hassle. 60 or 50% and it goes nuclear 45 or 40% and it slowly decays to nothing. Assuming these last couple graphs all have similar outside temps and same flue damper setting, IE similar draft for a given flue temp. it’s really tough to think what might be the issue.

I had two possible things to try, one was to close the damper based on flue temperature and not stove top temp… I almost exclusively cold start. With my setup, I can almost always get a good cat light off with a griddle temp <250 as long as I have the right flue temp-outside temp delta. This ensures that most of the initial off-gassing/catalyst warmup is dumped into heating up the cast iron. Note. This gives controlled catalyst light off, but produces minimal room heat.

The second suggestion was something we’ve discussed outside the group, but wood placement seems to have a huge effect in my encore. I wonder if you put something in the firebox to force there to maintain a gap between the wood and back wall. Maybe a rectangle of 1” steel. Then maybe you can leave the air at higher setting so it doesn’t crash and avoid having wood shift later in the burn and fall against the back wall. Would certainly want to pick something that isn’t going to pollute your catalyst and size it so that it can’t fall and break your glass. If there is always a gap such that smoke isn’t directly entering the engine, that should help your catalyst temp excursions.

Or maybe your metal cat is dead and you’ll be good tonight. Who knows?

Edit: prototype attached. View attachment 321130

Hey bud, thanks for the thoughts...

On cold starts I have been using flue temps as an indicator, notice on my pre-burns I engage the cat around 650F. Usually this puts my griddle temp right around 400 -450 anyway.

For the reloads notice the first one (the one that lit off) cat was engaged at flue = 400. The second one (the one that stalled) flue was at 500+.... so go figure.

Wood placement: Yep as we discussed before I always try to leave a space there at the secondary inlet. I like your idea there. I may have to scrounge around the shop and see what I got laying around for raw material.....

 

[sargeott]

@arnermd - man. What a hassle. 60 or 50% and it goes nuclear 45 or 40% and it slowly decays to nothing. Assuming these last couple graphs all have similar outside temps and same flue damper setting, IE similar draft for a given flue temp. it’s really tough to think what might be the issue.

I had two possible things to try, one was to close the damper based on flue temperature and not stove top temp… I almost exclusively cold start. With my setup, I can almost always get a good cat light off with a griddle temp <250 as long as I have the right flue temp-outside temp delta. This ensures that most of the initial off-gassing/catalyst warmup is dumped into heating up the cast iron. Note. This gives controlled catalyst light off, but produces minimal room heat.

The second suggestion was something we’ve discussed outside the group, but wood placement seems to have a huge effect in my encore. I wonder if you put something in the firebox to force there to maintain a gap between the wood and back wall. Maybe a rectangle of 1” steel. Then maybe you can leave the air at higher setting so it doesn’t crash and avoid having wood shift later in the burn and fall against the back wall. Would certainly want to pick something that isn’t going to pollute your catalyst and size it so that it can’t fall and break your glass. If there is always a gap such that smoke isn’t directly entering the engine, that should help your catalyst temp excursions.

Or maybe your metal cat is dead and you’ll be good tonight. Who knows?

Edit: prototype attached. View attachment 321130

Hey bud, thanks for the thoughts...

On cold starts I have been using flue temps as an indicator, notice on my pre-burns I engage the cat around 650F. Usually this puts my griddle temp right around 400 -450 anyway.

For the reloads notice the first one (the one that lit off) cat was engaged at flue = 400. The second one (the one that stalled) flue was at 500+.... so go figure.

Wood placement: Yep as we discussed before I always try to leave a space there at the secondary inlet. I like your idea there. I may have to scrounge around the shop and see what I got laying around for raw material.....

Im very interested to see if either of you or preferably both, put in a device to keep space for the smoke and gasses to freely flow into the engine.
I suspect flow blockage might be the issue. My resoning:

If there was an initial blockage as soon as you close the bypass the temps would crash and firebox would fill with smoke. If the blockage occurrs during the burn due to falling wood into the area where the exhaust needs to flow, this would make some sense.

@arnermd if your cat was dead, your engine/cat temps would be closer to your flu temps. The issue somehow surrounds the air fuel ratio in the firebox & or the cat area.
We have seen others @JohnDaileyNH for example do the manual secondary air control where he uses fresh air into the cat to lower temps.
Cats don't need much fresh air or any to do their job. BUT, there still needs to be flow of gasses passing the precious metals inside the cat which creates the chemical reaction to happen.
Think about vehicle exhaust cats. Those don't get fresh air into them to work. To much unburned fuel plugs them up or kills the material.

In my old job, i had worked very closely with Oregons only coal fired generation plant (RIP) before they demolished it. That plant was the cleanest burning coal plant on the west coast. They ran massive catalysts and amonia injection. They also monitored emissions in real time because OREGON is a big green state.
If the burners on the hot side the emissions were reduced and catalyst temps were lower, less amonia was injected and consumed. When we had to lower power output, the emissions were the same, but cat temps were very high and amonia consumption was higher.

Just my observations based on experiences.

 

[NewGuy132]

Something weird happening right now. I put a new cat in the stove last week and it’s been running a top. Today while I was at work the wife has been running the stove. She said good STT and cat in the 700-800’s all day. I get home and notice that the cat is about 600. 30 minutes or so goes by and now the cat is 520. I turn the air up and the cat jumps back to 600’s. I turn it down a little and now the cat is in the 400’s and the STT is 550.

We are going to let it go out and I’ll take a look at it in the morning. Feels like the bypass is a little loose, it is way to easy to close so I’m thinking that I don’t have a good seal.