Managing Temp Output with the VC Encore Cat

[JV_Thimble]

Always thought this was easy, until I recently installed one of the Condar thermal probes to monitor Cat temp. Stove manual says something along the lines of 400-500 F (stovetop) is low, 500-600 medium and 600-800 high ,and I've never had a problem with exceeding those temps.

Now that I've installed the Condar probe, however, I've found several times when the stovetop temp is 500 and the Cat is as high as 1850! If I cut the air to a minimal level, it tapers down after a bit. It seems in general that when I load the stove up with dry wood, that I can reach these kinds of temps fairly quickly. The solution seems to be to get the stove going fairly well, cut to ~1/2 air till it gets hot at the cat, then back the air all the way down. Once the Cat temp drops below 1,000 or so, then I can open up the air gradually till it's full on.

This works, but does require a bit more attention than I'm used to. And I don't like exceeding the max recommended Cat temp of 1700 - which seems quite easy to do.

Thanks in advance for you thoughts on this.

John

 

[JV_Thimble]

Ok, I take it that my operational protocol is generally ok.

At the moment, though, I'm sitting on minimum air with a cat temp of 1850. This is overtemp, and I don't like it. And stovetop temp is only ~520. Absent the Condar probe, I'd have no idea this was too hot, and would likely have the air opened up even more.

Suggestions?

 

[BrowningBAR]

Ok, I take it that my operational protocol is generally ok.

At the moment, though, I'm sitting on minimum air with a cat temp of 1850. This is overtemp, and I don't like it. And stovetop temp is only ~520. Absent the Condar probe, I'd have no idea this was too hot, and would likely have the air opened up even more.

Suggestions?

Feed it more air and I think the probe temps will drop. I think.

With the cat at 1850 what is the temp on the back panel of the stove that holds the cat and assembly?

 

[Gridlock]

I used to have that problem all the time with my Defiant; I actually saw CAT probe temps of 2300 degrees on a couple of occassions! In my situation, I had other issues including backpuffing which were all cured when I installed a new insulated 8 inch liner that replaced a 6 inch flex liner. I still occassionally see CAT temps of 1700-1800 degrees, but only when the firefox is stuffed to the gills. How packed is the firebox when you see those temps? Do you have any other draft related problems?

 

[JV_Thimble]

Thanks for the thoughts.

Didn't take a back panel reading with my IR this time, but have never found it to be very high.

Packed to the gills with wood when this just happened. Freezing rain changing to snow here.

I've had backpuffing once, but not since. Draft seems to be fine. Much better with the new insulated liner that was installed almost a year ago than with the old unlined masonry flue.

Once I back off the air, the cat temp levels off and eventually declines (may take an hour). It's 700 F now, so I just opened the air up to 1/2.

 

[JV_Thimble]

Ok, I take it that my operational protocol is generally ok.

At the moment, though, I'm sitting on minimum air with a cat temp of 1850. This is overtemp, and I don't like it. And stovetop temp is only ~520. Absent the Condar probe, I'd have no idea this was too hot, and would likely have the air opened up even more.

Suggestions?

Feed it more air and I think the probe temps will drop. I think.

With the cat at 1850 what is the temp on the back panel of the stove that holds the cat and assembly?

A bit afraid of opening up the air at high temps to try this out. Does this work for some of you folks?

 

[BrowningBAR]

Ok, I take it that my operational protocol is generally ok.

At the moment, though, I'm sitting on minimum air with a cat temp of 1850. This is overtemp, and I don't like it. And stovetop temp is only ~520. Absent the Condar probe, I'd have no idea this was too hot, and would likely have the air opened up even more.

Suggestions?

Feed it more air and I think the probe temps will drop. I think.

With the cat at 1850 what is the temp on the back panel of the stove that holds the cat and assembly?

A bit afraid of opening up the air at high temps to try this out. Does this work for some of you folks?

Others with more experience will be able to chime in. Todd and Leeaves I think both have probs and are pretty good with cat temps.

 

[Gark]

In the Encore, firebox (stovetop) temp is only loosely related to the cat burn. Ya can have no flame (low griddle temp) but if most/all the splits are outgassing, the cat gets serious hot handling the huge amount of smoke. What size splits is the stove being "loaded full" with? We don't have a cat probe so I can't address what you're seeing, but fewer much larger splits would generate less smoke than lotsa meduim & small splits. Also, what species of fuel is loaded when you see the real hot cat? Metal or ceramic cat?

 

[JV_Thimble]

In the Encore, firebox (stovetop) temp is only loosely related to the cat burn. Ya can have no flame (low griddle temp) but if most/all the splits are outgassing, the cat gets serious hot handling the huge amount of smoke. What size splits is the stove being "loaded full" with? We don't have a cat probe so I can't address what you're seeing, but fewer much larger splits would generate less smoke than lotsa meduim & small splits. Also, what species of fuel is loaded when you see the real hot cat? Metal or ceramic cat?

Thanks, Gark

Variety of species - maple, cottonwood, hickory, elm, ash. And generally larger pieces - mostly 4" and bigger. Cat is ceramic, newly re-installed about a month and a half ago under warranty. They must be all reaching peak outgassing at the same time, which would make sense with this batch loading process.

What amazes me most is that without the Condar probe, I'm sure I would be running this stove much hotter at the cat than should be done. Have seen someone else on these forums say this is essential to this sort of stove's operation, and I have to agree. And I only bought one after a badly warped cat and refractory box were replaced under warranty...

 

[Gark]

Thanks, JV_ Having read about experiences with the Encore on this forum & others getting warped firebacks and fried refractories, I have never loaded the stove completely. Without a probe under the cat, there's no way to know what's going on back there. The wood piled full in the firebox covers the hood (can't see it) so it could be glowing like mad. The only way we could limit cat overburn was smaller loads, splits as big as can fit through the doors, burn the fire from one end and restrict the amount of air coming into the EPA holes.

 

[JV_Thimble]

1950 F now. Air shut down, but will definitely be keeping an eye on this.

 

[pen]

That's hot enough to do damage to the cat.

pen

 

[JV_Thimble]

That's hot enough to do damage to the cat.

pen

Yes, I know. It was glowing. Down to 1600 now, about 2 hours later. I need to change something here. Wish this stove wasn't so finicky.

 

[JV_Thimble]

Since I'm following the written manufacturer instructions and having these problems, I'm of more than half a mind to make a warranty claim as a defective product. I don't think they'd actually go so far as to replace the stove, though. And such a fight would take heaps of time and energy. But I am still well within one year of purchase, and they have already replaced the cat and refractory box...

 

[JV_Thimble]

I had thought that if I shut the air down completely shortly after I closed the damper that things would work ok. I was wrong.

Start with damper and air control open full.
Clean out ash, and start off of coals.
Add some small wood scraps (from splitting) and some small diameter (<2â€) wood.
Then add mostly larger wood (3-5â€)

Check wood moisture content (fresh splits)
Maple 16.7%
Ash 15.6%
Elm 15.4%

Time Stovetop Temp Cat Temp
Start 190 Cool (<350) Add some wood
16:00 300 Cool Add more wood
16:06 325 Cool Last piece, stove now full
16:10 400 Cool
16:13 450 350 Close damper
16:14 450 550 Close air, flames die right down
16:23 400 1200
16:38 400 1600
16:45 375 1750 Too hot!
17:02 400 1850
17:12 450 1950

 

[Gark]

JV_ we've seen ours do the same in the 3 years it's installed. When you close the primary air handle all the way to the rear,by design (I think) there is still fresh air going into the firebox. Two EPA holes let air into the ashpan cavity. And when the air control is all the way to the rear, maybe your air shutter (lower rear of stove) is not fully closed. The white gasket between the shutter frame and stove body kept our shutter from closing completely. Whether this is intentional or design/assembly goof, I don't know.. we only half-load the stove. Still get all night burn. What also seems to slow the cat overload is burning from one end. For reload, I shove all/most of the coals to the far left (or right) and reload. This seems to let the fuel stack burn from one end to the other (somewhat) instead of all sticks outgassing at once and overfiring the cat. This is our first EPA stove after using a smoke dragon and this 2550 acts very persnickity compared to so many other stoves (have read hundreds of posts here & elsewhere). I give ours one more burn season....
It sounds like your cat is working too well. Rest assured, after it gets clogged with ash (weeks) and it suffers flame.impingement (see the flames going under the hood?) it will lose effectiveness gradually. Is your secondary air intake shutter operating smoothly and is the secondary bimetal probe burned away?

 

[Gark]

Just read your post about the innards glowing.. was it the hood and maybe even the upper fireback? Yeah, been there. I'm convinced there's no way a hot cat can make cast iron glow. Thus, (secondary fresh air comes up through channels behind the lower fireback and mixes with smoke BEFORE it all goes into the cat) the stove gets secondary combustion without the cat's help. Non-cat stoves do this on purpose. Ours does it by mistake. Suggest you try closing the damper sooner (say, 400 griddle temp. or 375). My owners manual says to close the damper right after a reload on coals, not to wait for griddle 450 before closing the damper. Worth a try....

 

[JV_Thimble]

Thanks for all of the thoughts, Gark. I'll see what I can figure out about the air controls, etc. Some really good operational suggestions. And I'll read the manual again to see if I'm doing everything VC says I should, as I don't recall the recommendation to close the damper down right after adding wood onto hot coals. I'm starting to lean towards closing the damper when the cat temp reaches 450 (light off temp) rather than paying any attention to the stovetop temp.

Overall, to me, though, this just smacks of poor design. I'm feeling like I should turn my operational woes into VC as a warranty claim while still in the first year of ownership. Goal would be to get an exchange for the Encore Two-in-one, but only if I were certain that it actually worked better.

One bit that I doubt is related is the gaskets around my fireback - https://www.hearth.com/econtent/index.php/forums/viewthread/83217/. They are in less than ideal shape. I was planning on replacing them at the end of the burn season, but let me know if you guys think it's essential to do right away.

John

 

[JV_Thimble]

Gark -

Some of your suggestions have been quite helpful.

Smaller loads works, but I am trying to get the stove to run on a full belly (as I think it should). I'm still in denial on this one...

Blocking one of the EPA-Holes (no pun intended) seems to help.

Burning from one side to the other (thought this was BS) turns out to be a big help.

Closing the damper early also seems to help.

Thanks,

John

 

[jharkin]

JV...Sorry to hear you are still having issues. You are not alone - Ive seen those temp spikes as well. 1800 a couple times and once 2000 when I wasn't looking. My stainless combuster is warped, but thankfully still works.

A few things Ive observed that may or may not help...

- Every time Ive seen temps over 1800 Ive also had the glowing hood and visible flames under the hood. I agree with the theory posted up thread - these temps ignite spontaneous secondary combustion before the cat which is what overheats the fireback.

- When I get 1700+ temps this is what I do:
#1 I immediately close the air completely. This usually does the trick and within 5 minutes it drops to 1650 or less
#2 If that doesn't work then I open the bypass and let it dump heat up the flue. Wait for the cat temp to drop below 1500 then engage on low air and watch it.

Every time Ive had the issue this has worked. In my 3rd year with the stove now and I have not had a scare this year even on full loads of 2+ year old oak and apple. As time goes on I guess you learn the tricks to avoid it.



The problem seems entirely related to dealing with full loads. Ive never had this happen on a 3 or 4 split load. To avoid the problem starting I have tried:

-I redid every gasket till they all seal tight enough to tear a dollar bill. Much better control

- Sometimes I find that if you let it burn down to few coals then start a full load and try and close the damper too early the cat will stall and just sit around 700-800... At some point it eventually takes off suddenly and the massive smoke volume sends things nuclear. It seems that waiting longer to get the load REALLY hot (700 griddle) and then turning the air down in stages allows a more gradual cat takeoff and may avoid this.

- Another option that seems to help is reloading earlier when the cat is still fairly active (800-1000) and the coal bed is big. You can shut down the damper early without smothering the cat and get it going before the entire load was charred. You have less smoke volume that way.

 

[JV_Thimble]

JV...Sorry to hear you are still having issues. You are not alone - Ive seen those temp spikes as well. 1800 a couple times and once 2000 when I wasn't looking. My stainless combuster is warped, but thankfully still works.

A few things Ive observed that may or may not help...

- Every time Ive seen temps over 1800 Ive also had the glowing hood and visible flames under the hood. I agree with the theory posted up thread - these temps ignite spontaneous secondary combustion before the cat which is what overheats the fireback.

- When I get 1700+ temps this is what I do:
#1 I immediately close the air completely. This usually does the trick and within 5 minutes it drops to 1650 or less
#2 If that doesn't work then I open the bypass and let it dump heat up the flue. Wait for the cat temp to drop below 1500 then engage on low air and watch it.

Every time Ive had the issue this has worked. In my 3rd year with the stove now and I have not had a scare this year even on full loads of 2+ year old oak and apple. As time goes on I guess you learn the tricks to avoid it.



The problem seems entirely related to dealing with full loads. Ive never had this happen on a 3 or 4 split load. To avoid the problem starting I have tried:

-I redid every gasket till they all seal tight enough to tear a dollar bill. Much better control

- Sometimes I find that if you let it burn down to few coals then start a full load and try and close the damper too early the cat will stall and just sit around 700-800... At some point it eventually takes off suddenly and the massive smoke volume sends things nuclear. It seems that waiting longer to get the load REALLY hot (700 griddle) and then turning the air down in stages allows a more gradual cat takeoff and may avoid this.

- Another option that seems to help is reloading earlier when the cat is still fairly active (800-1000) and the coal bed is big. You can shut down the damper early without smothering the cat and get it going before the entire load was charred. You have less smoke volume that way.

Thanks, jharkin

I've also found that opening up the bypass helps. As for shutting the air all the way down, it sometimes takes a couple of hours for that to work once I cross 1700. So I try and stay at or below that temp.

John

 

[jharkin]

Hmm if I'm just touching 1700 or 1750 closed air works fast.... Its only when it gets into the 1800 1900 range that it becomes hard to recover for me.

Wonder if you still have an air leak someplace. I assume you checked all the gaskets and main air flapper. Have you popped that small cover off the back to look at the secondary air intake flapper? Maybe its stuck open? Even cold its only open a hair... Its adjustable by turning the screw on the bimetallic coil but I cant remember the setting off hand.. Its something like setting the end of the coil at around 4 or 5 o'clock - which results in the flapper being only open 1/4" or less when cold.

 

[JV_Thimble]

Hmm if I'm just touching 1700 or 1750 closed air works fast.... Its only when it gets into the 1800 1900 range that it becomes hard to recover for me.

Wonder if you still have an air leak someplace. I assume you checked all the gaskets and main air flapper. Have you popped that small cover off the back to look at the secondary air intake flapper? Maybe its stuck open? Even cold its only open a hair... Its adjustable by turning the screw on the bimetallic coil but I cant remember the setting off hand.. Its something like setting the end of the coil at around 4 or 5 o'clock - which results in the flapper being only open 1/4" or less when cold.

Right, yes, recovery takes a while when at 1800 +. A bit easier now, though, with one EPA hole blocked.

The main and secondary air controls look ok to me - checked those a day or two ago. Gaskets inside the stove (around the fireback) need some work. I was thinking that could wait, but maybe not so...