Ran the first test fire in our new VC Defiant

[U235]

Thanks for pulling this up.. gave me a starting point..

The front should have already passed your area.. did it cool

For sure - Christmas came early! 46 this AM.
Was able to squeeze in two evening fires before we hit the road for a fall break trip.
I’ll be burning black locust all season - getting used to coaxing that demon to light…. Need to get some storage and shoulder season wood, but for now, just burning what’s seasoned.

 

[gthomas785]

Didn't read the whole thread - just a comment that if your bypass damper is open you will get full unregulated secondary air flowing straight into the firebox. To get the full range of control from the air lever, the bypass damper needs to be shut.

 

[DullAxe]

Hey all, thanks for the information and for pulling out the threads from Woodsplitter's comments in the 22-23 VC users thread.

And gthomas - thanks for information about not having full range of control over air unless the bypass damper is shut.

 

[arnermd]

Welcome to the forum. I am particularly interested in your experience, I have a catalytic Defiant (model 1975 installed in 2012) as well. I don't think there are too many of us with the bigger stove and I believe it burns a little different than the Encores, although the same basic principles apply and I think the refractory engine / cat is the same or very similar.

I think you got some good info here already but I will concur with @gthomas785, when you are burning with the bypass damper open the air control lever has very little effect. I have had the griddle temps over 600F with the air full closed, bypass open. Early on I contacted VC about this and their response was do not run the stove that way..... I do not leave the secondary bypassed unattended anymore and I have an alarm on my stove top temp in case I get distracted by other things.

I do see a huge difference if I leave the ashpan door open. It will draft like a mother..... I never leave the ashpan door open except for a very short time if I am trying get a load going quickly and only for a few minutes at a time. Lately I have been opening the front doors rather than the ashpan when lighting off from cold, it is much less dramatic.

I am very curious to see how your secondary burns go. Do you have a cat temp readout? If not, get one.

Best of luck and keep us appraised.

 

[AsylumResident]

@arnermd I also have the Defiant 1975 cat-c installed this last spring. I had about a dozen burns in it last March and am looking forward to this season of burning. I have run a handful of burns in the past two weeks and have found that leaving the front doors cracked to get things started quicker works well. I did open the ash pan door once to get things started but I have a feeling it could get away from you pretty quickly.

I just got my AT100 yesterday and did my first run with that. Had some good temps.

I’m glad there a few people here who run the bigger stove to bounce some ideas off of.

 

[AsylumResident]

Today on a hot reload cat was 550 and STT was 450 I loaded a little more than 1/2 full with primary air all the way open. After about one minute I closed the by pass and cat temp jumped to 1,000 within two minutes. When cat temp hit 1,100 I moved primary air to about 75%. The temp slowly climbed to 1,300 so I closed primary air to 50%. Continued slowly climbing to 1,450 then I could hear some of the wood move and shift, flames started dancing around like crazy and the cat temp shot up to 1,575 so I closed my primary all the way, then my glass went mostly black and cat got to 1,620. From reload to 1,620 was about an hour and a half. It hovered around 1,600 for about 10 minutes then very slowly came down. The STT never got above 550. Two hours in and cat is down to 1050, STT is 525 and the slightly more than 1/2 load is basically down to coals. I specifically checked MC on this load, which was about 13%. After this I understand when guys say they aren’t too concerned with STT.

Based on how this went I’m assuming I should have dialed the air back sooner.

Do you have issues with glass going black with higher cat temps, lower MC, and decent STT temps? Should I be going through that much of a load in 2 to 2.5 hours? Wood too dry?

 

[Woodsplitter67]

Today on a hot reload cat was 550 and STT was 450 I loaded a little more than 1/2 full with primary air all the way open. After about one minute I closed the by pass and cat temp jumped to 1,000 within two minutes. When cat temp hit 1,100 I moved primary air to about 75%. The temp slowly climbed to 1,300 so I closed primary air to 50%. Continued slowly climbing to 1,450 then I could hear some of the wood move and shift, flames started dancing around like crazy and the cat temp shot up to 1,575 so I closed my primary all the way, then my glass went mostly black and cat got to 1,620. From reload to 1,620 was about an hour and a half. It hovered around 1,600 for about 10 minutes then very slowly came down. The STT never got above 550. Two hours in and cat is down to 1050, STT is 525 and the slightly more than 1/2 load is basically down to coals. I specifically checked MC on this load, which was about 13%. After this I understand when guys say they aren’t too concerned with STT.

Based on how this went I’m assuming I should have dialed the air back sooner.

Do you have issues with glass going black with higher cat temps, lower MC, and decent STT temps? Should I be going through that much of a load in 2 to 2.5 hours? Wood too dry?

When you turn your air all the way back your glass will turn black. This should not be a surprise as there is no air and you are purposely starving the stove for air for a longer burn. Blaze kings as well.as others do the same thing.. black glass when turning the air down. The thing is that your glass should stay clean when the air is half way..

 

[arnermd]

Agree with @Woodsplitter67 on the blackened glass, pretty common with low air settings.

Welcome to the 1600+ club.... I want to be clear that I do not know the answer to your questions with certainty, but here is what I think...

• I think 1600 is too hot (some folks might disagree, but I like to see cat temps 1100 - 1400)
• I suspect you should have throttled air back sooner, one thing I learned from @Woodsplitter67 is the initial state of the burn sets the tone for the load. If the whole load is ripping when you throw the bypass in it is very hard to get it back under control, especially when everything is good and hot.
• If you have a nice bed of coals going and cat is up at 500+ I will often load it and immediately close bypass, throttle the air back in a few minutes.
• Hot reloads are very prone to cat overtemps in my experience. I suspect it is because the whole load just goes up at once. Dry wood will make this even more pronounced I think.
• I have a suspicion that our stoves are more susceptible to this because the firebox is bigger and the secondary engine is the same. More fuel through the same size cat = hotter.
• I also wonder about the secondary air flow, I suspect on our stoves it is too low. Increasing the secondary air will decrease the temp.
• One of the things I do not like about these designs is that secondary air flow can mix with the primary burn and it is uncontrollable. I would much prefer the secondary air to be completely isolated from the primary burn zone, older VC's were designed to prevent this.

Things I have experimented with to recover from 1600+ cat temps

• Close the pipe damper to reduce draft. If you do not have a key damper in your exhaust you may want to consider adding one. I actually changed mine last year to a solid plate and made a seal around the disc so I can really clamp down on the draft. I have 8" pipe and ~25 feet of 8" liner. This is risky, as you can have smoke coming back into the house, so never leave the exhaust clamped down unattended.
• You can make a plate to block the secondary inlet and hold it in place with magnets. This works pretty well and avoids having the close off the outlet.
• If all else fails, open the bypass damper, but be ready for some big fire ripping up the exhaust pipe..... This is where the key damper comes in handy to cut back on the draft.

Good luck and let me know what works for you.....

 

[DullAxe]

I received my Auber AT100TC last Thursday, forgot to install it before starting a fire on Friday night. The weekend was too busy so I didn't get around to it. My in-laws just showed up, so I won't get to it until they leave...hopefully in a couple of days.

We have had a couple of fires now where we engaged the cat and, as gthomas mentioned, the air control was much more responsive when the bypass was closed.

 

[AsylumResident]

Agree with @Woodsplitter67 on the blackened glass, pretty common with low air settings.

Welcome to the 1600+ club.... I want to be clear that I do not know the answer to your questions with certainty, but here is what I think...

• I think 1600 is too hot (some folks might disagree, but I like to see cat temps 1100 - 1400)
• I suspect you should have throttled air back sooner, one thing I learned from @Woodsplitter67 is the initial state of the burn sets the tone for the load. If the whole load is ripping when you throw the bypass in it is very hard to get it back under control, especially when everything is good and hot.
• If you have a nice bed of coals going and cat is up at 500+ I will often load it and immediately close bypass, throttle the air back in a few minutes.
• Hot reloads are very prone to cat overtemps in my experience. I suspect it is because the whole load just goes up at once. Dry wood will make this even more pronounced I think.
• I have a suspicion that our stoves are more susceptible to this because the firebox is bigger and the secondary engine is the same. More fuel through the same size cat = hotter.
• I also wonder about the secondary air flow, I suspect on our stoves it is too low. Increasing the secondary air will decrease the temp.
• One of the things I do not like about these designs is that secondary air flow can mix with the primary burn and it is uncontrollable. I would much prefer the secondary air to be completely isolated from the primary burn zone, older VC's were designed to prevent this.

Things I have experimented with to recover from 1600+ cat temps

• Close the pipe damper to reduce draft. If you do not have a key damper in your exhaust you may want to consider adding one. I actually changed mine last year to a solid plate and made a seal around the disc so I can really clamp down on the draft. I have 8" pipe and ~25 feet of 8" liner. This is risky, as you can have smoke coming back into the house, so never leave the exhaust clamped down unattended.
• You can make a plate to block the secondary inlet and hold it in place with magnets. This works pretty well and avoids having the close off the outlet.
• If all else fails, open the bypass damper, but be ready for some big fire ripping up the exhaust pipe..... This is where the key damper comes in handy to cut back on the draft.

Good luck and let me know what works for you.....

I appreciate the details. I have been reading the entire 2022/2023 VC thread a piece at a time continuing to learn from others experiences.

Based your comment of increasing the secondary air would decrease the temp, why is that? I feel like I don’t have a decent understanding of the secondary air.

 

[arnermd]

I appreciate the details. I have been reading the entire 2022/2023 VC thread a piece at a time continuing to learn from others experiences.

Based your comment of increasing the secondary air would decrease the temp, why is that? I feel like I don’t have a decent understanding of the secondary air.

Adding secondary air will increase the cat temp until you achieve Stoich mixture, at that point you have just enough oxygen to combust all the fuel there is. If you add more air you are burning with excess air which just dilutes the heat of combustion and thus lower temps.

This all assumes there is a fixed amount of fuel for the cat to combust. If some of that extra air goes to the primary burn zone it will create more smoke (fuel) for the cat. This is why I do not like that our secondary air goes into the primary burn chamber. I would much rather see it be separated.

Last year I did a schematic that describes the air and smoke flows.
Post #1084

 

[AsylumResident]

Adding secondary air will increase the cat temp until you achieve Stoich mixture, at that point you have just enough oxygen to combust all the fuel there is. If you add more air you are burning with excess air which just dilutes the heat of combustion and thus lower temps.

This all assumes there is a fixed amount of fuel for the cat to combust. If some of that extra air goes to the primary burn zone it will create more smoke (fuel) for the cat. This is why I do not like that our secondary air goes into the primary burn chamber. I would much rather see it be separated.

Last year I did a schematic that describes the air and smoke flows.
Post #1084

Thank you for the schematic. I have been looking for exactly that since I got this stove. I figured after this years burning season I was going to break the stove down just to see it all and try to get a better understanding of it.