Vermont Castings Burn Observations

[bullittman281]

Hello everybody,
WARNING LONG!

I have some general observations that don’t quite fit in the year performance thread and I don’t want to hijack any threads so a new thread it is.

I have had a bunch of free time to browse the forums and have some observations based on my own experience and the experiences here. I have a Dauntless with out the cat. It seems most here run all the VC stoves with the cat installed, whether mandated or not in the flex burns. Most seem to run temperature monitoring well beyond the included factory “probe”. The results every body posts are wildly varying and inconsistent. First observation is the stoves are hard to run. Obviously. But I have some of my own ideas.

The design of these stoves are a secondary burn stove possibly with a catalyst for final clean up. This is unlike, say a blaze king, where there is no secondary air tubes or burning and the entire premise is the catalytic combustor does all the “burning” and the fire intentionally smolders. Somewhat of a big difference. In theory, the majority of the energy release in a VC stove should happen in the so-called refractory engine, not in the catalyst. Or at least during higher burn settings. I believe this is where the problems start. The secondary burn in these stove is temperamental at best. Its not just VC. The lopi Lyden at the time was the same or worse for this.

I have a theory that the incredible temperature spikes on the catalyst people see are because secondary combustion never lights off and the cat has to cash the entire energy check. This is fine at a low burn rate. Not so fine at higher rates when it should have some support. My stove is very easy to tell if it has good secondary combustion or not because the combustion is not silent and the smoke output is tremendous if it doesn’t light. The fix is to re-arrange the wood and fiddle with the damper and air control. Everybody running a catalyst may not notice this except for spiking catalyst temps. This brings us to the combustors.

Vermont Castings seems to run only 2 or 3 refractory engines for all four models. The part number for Intrepid and Dauntless refractory parts are the same part number and the Defiant and Encore share some ceramic pieces. The large fire box for the combustion package seems to not work as well. The Dauntless and the Defiant. No hard science, just an observation. The Defiant crowd seems to kill catalysts the best. It could be that the larger fireboxes are simply too large for the combustion package. I think of all of the stoves the Encore hits its marks the best, but even it has its issues.

For burn characteristics I know I have to follow the manual EXACTLY to get my secondary combustion to light off. The shoveling and piling of the coals are very real. It wont go if I don’t shovel the coals to the back. The wood has to be piled tight against the back of the stove for it to light. If not, no secondary combustion and prodigious smoke. The stove shop I worked with had a Defiant on display. Their Defiant had the seemingly typical sloppy front cover so it was possible to see through the gaps and see when the secondaries lit with a blue-yellow glow. That stove seemed to light MUCH better than the dauntless but their display wood is stupendously dry pine, so that may be a factor.

I guess all if this is to say that maybe the temperature problem is a secondary burn problem. For those interested in experimenting it would be interesting to see if the cat behaved better if great effort was made to ensure secondary combustion actually lit. Maybe it does and I’m just delusional. I know many smart people have many hours trying to make these things work better.

One last note on glass clarity and back puffing. For me, maintaining an air setting that keeps SOME flame present in the firebox is critical. With out that the glass gets truly annihilated and the thing is liable to back puff like crazy. A bit more air calms all of these problems right down.

If you made it this far, hopefully its worth while and can help.

 

[VRB Farm]

Nice post! I think the issue with people running the defiant is they try and run the stove to low. That stove is a power house of btu production, folks try and cut it back way to much or run smaller loads. Sizing the stove to the application seems to get missed for cosmetics and not thinking the smaller box won’t produce what they need.

 

[dmccoole]

I'm going on my 5th year with the Encore and the temperamental operation of the cat still mystifies me! I had 30 years with a Noble(non cat) stove prior. I cut most of my firewood, burn 2-3 cords per year and burn 24/7 during the winter months.

With a good base of coals, I can usually get the cat to light off quite easily. I have troubles with the wide temp swings from burn to burn with the same wood, outside temps, wind, etc. From my observations, whatever is controlling the air to the cat is not working correctly for my stove or my setup.

But you have an interesting thought on "cashing". When I add splits on a hot reload, I have seen my cat temp at ~1000 but a lot of smoke coming out the chimney. The smoke will last 15-20 minutes and then goes smokeless. I'll try to keep my eye on the smoke levels during the day and try to correlate to temp swings. I've also observed my cat running in the 800 range for extended periods on the end of a burn. Is that really burning all the smoke or is it now cashing? Keeps my engineering skills engaged for sure!

 

[arnermd]

Nice write up and interesting thoughts.... I am not sure if I agree or not, but the lack of secondary burn is a new idea I think....

 

[bullittman281]

dmccoole, this is sort of what I'm talking about. In theory, on a hot reload the secondary combustion unit is well heated and should be ready to secondary burn nearly immediately after a reload when it gets fuel to burn (smoke). If it did light off there should be zero smoke, catalyst or not. Instead, the cat goes wild because its WAY over worked. A cat that is HOT, not over whelmed, and has a good air supply should not let any appreciable amount of smoke through it. I'm guessing the mid burn temp spike people see is the secondary combustion stalling. With out a cat this is when the fire smolders out as the stack goes cold and everything gets coated in tar. With the cat the stove powers through it, at the expense of very high temps. Again, just a theory. The late stage 800* you speak of sound the most correct and normal. Temps coming out of the fire box will be the hottest with only coals and the cat cleaning up whatever is left.

For somebody that has time, good weather and adventurous, pull that cat out and run a couple of small reloads. See what the smoke level does. Its not a completely fair test as the airflow through the stove is different with and without the catalyst in place. you WILL know if it has secondary burn or not with the catalyst out. Not sure how hot the temp probe would be with direct flame impingement.

When I get a change I want to add an EGT probe to my Dauntless even though there is no cat to monitor. I'm really curious whats going on in there. I intend to use a raspberry Pi for a low buck solution. I've added a couple of random pics and video of the stack that may help people out as well. These are a sequence of loading the stove only a few minutes apart. The movie was shortened so its time stamp is wrong. Hope this helps

 

[bullittman281]

Nice write up and interesting thoughts.... I am not sure if I agree or not, but the lack of secondary burn is a new idea I think....

I welcome disagreement and discussion. Thats the intent. Other stove brand don't seem to have these problems. SOMETHING is going on. Maybe this will help find a reason and a fix.

 

[arnermd]

I welcome disagreement and discussion. Thats the intent. Other stove brand don't seem to have these problems. SOMETHING is going on. Maybe this will help find a reason and a fix.

Agreed... "Something" is going on! I have been dealing with that "something" for 13 years.... Have not found it yet.

Please do not take my comment as criticism of any kind. I 100% support the discussion here.

I am so fed up with my ceramic cat right now I may pull it this afternoon..... Will report back.

 

[skb31]

I’ve run my Encore 2040 cat-c extensively without a catalyst. You can easily achieve smokeless burns and high refractory chamber temps with secondary ignition. You seem to sacrifice longer burn times is what I have noticed.

 

[AsylumResident]

I have never run my Defiant without the cat. I have begrudgingly been running much smaller loads so I don't have to deal with the run away cat temps, however it has been difficult to get my cat up to good running temps. I have been interested in running awhile without the cat to see how much build-up I actually get in the flue.

But great discussion. Since I have been on here I don't believe this specific item of the secondary burn has been addressed in this manner. I am very interested to see where this leads. But let's say you have properly diagnosed the issue, what would a solution be? Sell my Defiant?

 

[Smokey Da Bears]

It's interesting for sure. You've got the attention of 3 Defiant owners in @arnermd , @AsylumResident , and myself.

I recently did completely destroy a catalyst which I know we all enjoyed the pictures. I had a metal catalyst go 2.5 seasons before and my stove operation was all over the place as I was learning and experimenting. That catalyst demonstrated it's ineffectiveness by not having temps in the secondary above 900 and visible smoke in the exhaust. As soon as I replaced it, it was obvious. But the replacement catalyst didn't last a full year and was warped beyond what others had ever seen. But what was really interesting to me is @arnermd hit some temps 200 degrees above my maximums and didn't have any frame warping. So was my warping truly an operation issue, a design issue, or was it a catalyst lot build quality issue....no idea. It is what it is. I will say that Midwest Hearth after seeing the picture of the warped catalyst openly said "we've seen worse".

I also have never run my stove without a Catalyst installed and up until this point, hadn't even considered giving it a go nor do I think I'm willing to introduce the new variable.

The only thing I would add is that I can actually see the orange/blueish catalyst glow when looking in through the glass at the the top of my front access cover when my catalyst is lit off, at least with secondary temperatures above the 1000 range. This is not to be confused with flame impingement, as I've certainly seen that too. And have on many occasion rearranged the firebox to try to reduce that from a burn cycle.

Anyway, good discussion. I'm interested in and appreciate all of your opinions.

 

[bullittman281]

Howdy,
My thoughts would be to try to improve the odds of secondary combustion actually happening. On the smaller dauntless it takes carefully piling the coals and stacking the wood tight against the back wall. It take stacking the wood so some of the flame gets ingested as a sort of pilot light to keep the secondary burn lit. At least until the combustor gets screaming hot. It burns itself completely white after a good run. Secondary combustion is noisy and obvious with the lack of smoke. I wonder if the bigger stoves are the same. A test would be to make sure the mouth of the rear burner is buried in coals at reload time. Maybe this has already been tried. The manual does not offer much on coal management or wood placement for the Defiant. The instructions for the Encore are the same as the smaller Dauntless. The Encore uses at least some of the same part numbers as the Defiant for the combustor. It also has language that the catalyst is not required but recommended. Should anybody pull the catalyst for testing, I would consider removing the temp probe and using small loads. I'm not sure if the temp probe would get direct flame impingement or how much it would appreciate that. I don't have the big stove to test with. When I get a chance I want to build/install a temp probe for my Dauntless, despite not having a cat. I'm curious what the temps are and what they do with secondary burn. More to come on that.

 

[Woodsplitter67]

Me personally I think it has to do more with the wood off gassing more then anything. I know my cat is lit, sometimes the wood catches differently. I see my cat never going over 1450 on some burns. Most days it's hanging 12/1300. Others the cat will hang around 1k then spike, not because the cat isn't lit, because a 1k it most definitely is. Mostly it will spike because not a lot of wood caught in the beginning. That's what I see

 

[AsylumResident]

I will run an experiment, hopefully tomorrow, with piling the coals as you have explained to see what changes occur. I haven't even lit my stove today, highs in the upper 40's but tomorrow is back down to a high of 18. Love my Wisconsin weather!

 

[Smokey Da Bears]

I will run an experiment, hopefully tomorrow, with piling the coals as you have explained to see what changes occur. I haven't even lit my stove today, highs in the upper 40's but tomorrow is back down to a high of 18. Love my Wisconsin weather!

It's the same situation here today and tomorrow. My stove is cold today too.

 

[Woodsplitter67]

I'm not burning today. High of 60. The temps will fall today. I needed to clean the stove anyway, so good timing. The stoves been running a lot so far. Iv gone through roughly .75 of a cord

 

[arnermd]

I have seen a difference pushing coals against the secondary inlet. In general the cat heats up and lights off faster, but as always it is not real consistent. I don't always do it because I think it leads to a higher occurrence of over temps.... but I am not sure of that.

 

[AsylumResident]

Last week I finally got through all that maple I had, about a cord total. I'm now burning red oak and ash at 14% for the last week. What a difference! Very consistent, no high spikes. Still get an occasional back puff a couple hours into the burn but very minor. It was in the 40s here yesterday so I did a full clean out. Cat looked good with only a slight warp on the frame. It was 35 out when I lit the fire after sunset. Fire ran great last night though very warm in the house this morning. Cat was at 550 after 9 hour burn. Going to be upper 50s here today so I'll let it go out again today.

Sounds magical. When I'm on here and read words like 'consistent' and 'no high spikes' it makes me feel good inside. Brings me a happiness I never would have anticipated until I bought it VC stove and found my way to this wonderful website.

 

[dmccoole]

Sounds magical. When I'm on here and read words like 'consistent' and 'no high spikes' it makes me feel good inside. Brings me a happiness I never would have anticipated until I bought it VC stove and found my way to this wonderful website.

It was only a week but my hopes are up!

 

[Woodsplitter67]

I have seen a difference pushing coals against the secondary inlet. In general the cat heats up and lights off faster, but as always it is not real consistent. I don't always do it because I think it leads to a higher occurrence of over temps.... but I am not sure of that.

Your right about it. I tend to do that in shoulder season when draft is low

Doing that with an encore or defiant is a no no in winter especially when it's cold. In winter it's best with an even layer of coals not piled up