High catalyst temperatures on VC Defiant Encore

[OlyRon]

Hi. I'm new to the forum, and hoping that someone may have the experience to tell me whether I should be concerned about my cat temperatures.

I bought a new VC Defiant Encore in the late 90s, and ran it for a number of years without really knowing what I was doing. Over time, the cat went bad, internal castings warped, and performance became poor. Since we basically like the size, and couldn't find a similar cast iron top loader in a new stove, I decided to rebuild the VC. This was also about 1/4 the cost of a new stove. So, I installed a new fireback kit from Wooodman's and a Steelcat from Condar, made sure all the gaskets were tight, and replumbed my outside fresh air supply. I also installed a digital temperature monitor from Auber Instruments - the VC had a port for a cat probe, but never had one installed, and the standard mechanical gauge would not be easily visible behind the stove. The digital meter is trick, as it can be set to give maximum temp during a burn, so if I leave the stove overnight, I can see how hot it gets. It's also fun to watch the cat kick in when I close the damper.

Soo... What I'm seeing is that I can easily regulate my stove to comfortable temperatures, with the stovetop at 350-400F and pipe a foot above the stove around 300F, air lever slightly cracked open. However, my cat temps shoot up to what seem to be the danger zone, over 1500F. The max I've recorded was 1720F on a full load overnight burn (8-9 hours)with the air shutter fully closed, no visible flame in the firebox. The temperature gradually decreases as the load burns down. With a fully closed air setting, my stove and pipe temps drop to 350F and 275F respectively, so I'm nervous about getting creosote - but, none so far. No smoke from the clay flue masonry chimney, and much reduced ash compared to before rebuild. I cleaned the chimney last week.

So far, after a week of burning, it doesn't seem to have affected the cat, but I'm concerned that it will. I'm burning two year old alder and maple seasoned outside under cover. Also, I've confirmed that the new secondary air probe is working properly, closing the shutter at cat temp of around 600F. I'm sure I have some tiny air leaks, as the fire doesn't just die when I close the primary all the way, but I don't think they are significant, since my box temps are good.

Glad for input if anyone has an idea here - I can't think of anything else to do except maybe find some green wood! Thank you.
Ron

 

[Diabel]

Hi Rob,

Welcome to the forum.

To me what you are describing sounds pretty normal. My cat will hit 1700 once in a while (not sure why). It will easily reach 1500 on each load.

 

[jetsam]

1700 is pretty hot, but new cats do get pretty hot. They calm down as they age. Condar recommends keeping jt under 1500°, and Firecat suggests 1400° as a maximum.

I'd try to keep it under 1500 without worrying too much if a new cat briefly goes higher once in a while.

 

[OlyRon]

1700 is pretty hot, but new cats do get pretty hot. They calm down as they age. Condar recommends keeping jt under 1500°, and Firecat suggests 1400° as a maximum.

I'd try to keep it under 1500 without worrying too much if a new cat briefly goes higher once in a while.

I was wondering if it would sort of break in. There really isn't anything I know to do about it, so my attitude has been just to run it and see. I did contact Condar, and the manager there said that the Steelcat could take higher temps than ceramic, but that I was getting in the danger zone.

Thanks to you both for your thoughts

 

[defiant3]

So when you did the rebuild, did you remove and reseal the top? That's a thing many times on Encores, the exterior box doesn't need rebuilding as with older models, but the cement around the top casting seems to deteriorate. Also, if you have a 2190 or 2550, the back corner seams where the sides meet the back can become compromised when you remove the upper fireback and damper assy. SSSSSStrangely, its the 2 bolts that hold the upper fireback that also tie the sides and back together. Having the top on does keep everything in place, but the back seams should get a good squirt of cement just to be sure they're filled in.

Finally, though it's "cheating", you can fill in the bleeder holes in the ash pan area. They are 5/16" holes drilled vertically through the sides of the base which provide a constant flow of primary air. Probably on a stove that old there are enough places where air sneaks in, so go ahead and plug 'em.

This is just basic stuff, and these are not all necessarily things that feed air to the cat., but every bit helps in Encores so they really can't be too tight. It sounds like you got it right during the rebuild basically and there may actually not be a significant problem. I never liked those metal cat.s for the record mainly cuz they don't seem to last as long. Maybe they just like it hot! Some do I'm told...

 

[OlyRon]

I did not remove the top. A bit of cement came out of the back corners where the upper fireback attaches. I was concerned about how well the new assembly would seal, so I gooped up the channels in the back pretty heavily. Still, I'm sure there are some small leaks in the stove. I'll plug those bleeder holes, although I believe those just feed air to the box. I'm guessing that there is also leakage around the shutter for the secondary air vent. It's as good as new, but it's not a tight design.

I'll see what kind of life I get out of this cat, and think about a ceramic one the next time.
Thank you.

 

[RandyBoBandy]

You should head over to the VC owners thread and do some reading. There is some good info in there. When the stove is cold check the timing of your secondary air shutter. Where the rod connects to the coil is what you are looking for. If not timed correctly the coil will end up expanding to far and start open the shutter again allowing more secondary air in and sending the cat into orbit. Some guys have even disengaged their secondary shutter by removing the rod. And some have even taped over the opening with foil tape. What dive splits are you burning? Larger splits will help control cat temps as well as keeping a good layer of ash in the firebox.

 

[OlyRon]

I looked at that forum. and it seems to be for models older than mine, but perhaps some are the same. Mine is a 2550. I did not find a search function that was specific to that forum, but I'll try to peruse the threads when I have time.

I did what you suggested - the secondary air was not opening too far when hot, but I did remove the rod and taped it closed, as it was sloppy. On one load so far, it definitely took longer for the cat to accelerate in temperature, but it still reached a peak of 1670F about 1 hour into the burn. Taping the shutter definitely tightened the stove some, as I had to give it more primary air. With primary air turned down all the way, I got some puffs of smoke out the griddle that stopped when I cracked the air open, so I think the stove is pretty tight. No smoke leaks out the back corners during this, a trace from the doors.

My wood varies, but I'm mostly burning larger stock when the stove is warmed up. Seems to help a bit.

I'll report back after a few cycles of wood.
Thanks

 

[OlyRon]

So, just to add what bit of info that I can. After several days of burning, the blocking of the secondary air seems to take a bit off the peak temps, with max now in the 1450-1600 F range, none in the 1700 range. Definitely slowed the kick-off of the cat when started from cold, and does take more primary air. The stove is most stable if I burn it half full and throw in a couple of splits from time to time. This works well when I'm around. I do get 8 hours on a full overnight load, but the peak will be in the 1500s at 45-90 minutes.

Btw, this stove does not have bleeder holes in the ash tray area.

I'd be interested in whether others have a parallel experience with their 2550.
Thanks again for the suggestions.

 

[Diabel]

The 2550 has two air holes on each side of the ash pan. When the stove is cold, open the ash door and you can feel them with your finger. They are very hard to see from the outside of the stove.