What's Going On With These Crazy Hot Cat Temps?!?!?

[Ralphie Boy]

I’ve had my Buck 80 since January of this year and it has been both a blessing and a curse. When it’s right it’s great; plenty of heat and 12+ hour burn times. Maybe I’m just still in the new dumb operator mode, but I seem to have problems keeping the cat temps down to what I think is a safe level.

This is what I do: When starting a fire from a cold stove, which does not happen this time of year very often, I begin with a few small pieces and a quarter of a Super Cedar and let things get going fairly well. Then I add enough splits to fill the box and leave the air controls wide open until things get rolling at a good pace. Once the cat probe reads about 600, I set the timer for 20 min, and sometimes, slightly close the air controls. Once the cat has stayed 600 for 20 min I close the bypass and the air controls. It will hang at anywhere between 1200 and 1400 for long enough for me to be lulled into a false sense of security and leave the house to walk my property for 15 or 20 minutes. Upon my return I find the cat temps approaching critical mass and it’s “Quick, pull the bypass!” Once the temps fall to 1200 to 1300 I close the bypass again. Within a few minutes the temps are at 1500 at which point I pull the bypass again, even though it’s technically not too hot. I may do this 3 or 4 times before it settles into about 1400.

To reload a hot stove I usually wait until there is nothing left but a nice bed of coals and a cat temp of between 800 and 1100, then I fill the fire box as full as I can, after raking the coals forward, and close the bypass. At this point I’ve tried leaving the air closed, a quarter and one half open with seeming no different results, except at one half or more open it just gets hotter faster
.
I have my burns timed so that I reload about an hour before bed. It’s the same ritual as above with the same results; open, close,open, close. God only knows where the temps go after I hit the rack! It actually seems worse this burning season than last season.

Here is what I’ve done, besides read, to try to correct the problem: Replaced the cat probe….three times! I figured common things are common, maybe the probe is off. The second probe from Condar had one burn and stuck at 800! They promptly replaced it with the third probe, so really I have no idea how accurate either the first or third probes are. Believe it or not, I replaced the cat and gaskets and still nothing better. Most likely a foolish expense but what the hey, I’ve got an extra cat for when I need it. Someone said when it gets hot, don’t open the bypass but open all the air controls wide open, tried that and that’ a no, no, unless you want to smelt iron!

So what goes on here; what am I doing wrong! Too much wood? Why have a 2.5 Cubic foot fire box if you can’t fill it? Besides I can get almost the same results with 3 splits and some coals as I can with 8 splits and coals.

BTW: burning ash split and stacked, single row for 2+ years.

 

[Highbeam]

What is the problem? There's a reason you have numbers up near 2000 on your cat probe, they get hot. Let it run, mine will often glow bright orange and also be up over 2000 on the gauge.

There was a time when these things didn't even have cat temp gauges.

 

[weatherguy]

What do you consider critical mass? I know with mine if I wanted to run it cooler I'd just turn the air down quicker and let it creep up a bit but doesn't go too far, not sure if that would work for you.

 

[Ralphie Boy]

What do you consider critical mass? I know with mine if I wanted to run it cooler I'd just turn the air down quicker and let it creep up a bit but doesn't go too far, not sure if that would work for you.

I call 'critical mass' a notch over 1500 . I've read and been told by Applied Ceramics, the people who make the cat, that at 1600 damage to the cat can start.I've seen it hit 2000 more than once. I usually keep the air cut back all the way. I've even adjusted the aircontrol slides to reduce the air flow thinking it was getting too much air when fully closed. However I'm still closing in on 1600 many time before things settle at around 1400.

 

[weatherguy]

Ralphie, do you have a super strong draft?

 

[Ralphie Boy]

Ralphie, do you have a super strong draft?

My house was built in 1998 and is pretty tight. When it was an open fireplace we had problems with smoke rolling out. The stove has an 8 flue and was a professional install but anything is possible. I've seen some posts about an 8' flue creating an exceptional draft. I'm not sure how I check for a strong draft. Any suggertions?

 

[Kool_hand_Looke]

Draft checker, manometer?

http://m.grainger.com/mobile/product/DWYER-INSTRUMENTS-Manometer-2T650

 

[jharkin]

Condar says anything over 1700 will start to destroy the catalytic coating.

 

[rdust]

I just let mine burn, I don't put much faith into the cat probe once the stove is warmed up. I just use mine as a guide on when to close the bypass on start up. If you're running the stove the way the manufacture designed why worry about the cat temp? I'm sure they ran the stove much harder than your are during r&d.

Larger splits will slow the offgassing down which should keep the cat temp lower.

 

[davidmc]

I had the same concerns with my 91. I called Buck and they told me not to worry and let her work because the cat was good well past the 2000 on the thermometer. That was 3 years ago and mine has seen 2000 more times than I can count. Just my 2 cents.

 

[jharkin]

I had the same concerns with my 91. I called Buck and they told me not to worry and let her work because the cat was good well past the 2000 on the thermometer. That was 3 years ago and mine has seen 2000 more times than I can count. Just my 2 cents.

Im suprised they said 2000 was OK, as most catalytic element manufactures say thats far too hot. I once had mine get away from me to 2000, the result was glowing cast iron inside the stove and a warped cumbustor. I'm amazed I didnt warp or crack one of the interior castings.

 

[pgmr]

Is the door gasket tight? Is the bypass damper shutting all the way (can't see it when the door is closed, so you might need to wait until the stove has cooled)? Is the ash pan gasket intact?

It sounds like you have either too much draft (long flue?) or uncontrolled air leak.

The model 80 has a secondary air system that feeds air directly to the cat. The perforated angle iron behind the cat housing is fed from channel iron welded to the outside of the firebox to preheat the air. You can see this channel iron if you remove one of the sheet metal corner pieces. If you have excessive draft (long flue or bypass damper that doesn't close completely), you might be getting too much air through these secondaries.

 

[Ashful]

I've done a bit of reading on this, and it seems most / all cat manufacturers state that prolonged temps at or above 1800F will significantly shorten the life of the cat. What happens at this temperature is that the precious metals plated onto the ceramic substrate begin to delaminate from the substrate. This won't kill the cat instantaneously, but seriously shortens its life.

I have noticed with my own stoves is that if I get the fire going to vigorously before engaging the cat, then my cat may want to go high (1700 - 1800F is as high as I've seen mine go). The reason for this, I suppose, is that you've gotten the wood off-gassing at a very rapid rate, and the cat must try to process all of that fuel. If you shut down on the air control to stop it, you may see back-puffing. If you open up the air control, the reaction continues at it's rapid pace. The only answer is to reduce the throttle incrementally, trying to maintain the cat below 1800F. Over time, I learned to NOT let the fire get going quite that vigorously, before engaging the cat.

I say all of this because I don't understand why you'd leave the stove run in bypass for 20 minutes AFTER the cat has already reached light-off temperature. Why not just engage when the cat hits 600F? I think this should help you avoid the over-temp situation, unless I'm misunderstanding something.

 

[Highbeam]

I call 'critical mass' a notch over 1500 .

You are trying to fix a problem which does not exist. Further, your instrumentation is unable to accurately measure temps at that level.

 

[pgmr]

... I say all of this because I don't understand why you'd leave the stove run in bypass for 20 minutes AFTER the cat has already reached light-off temperature. Why not just engage when the cat hits 600F? I think this should help you avoid the over-temp situation, unless I'm misunderstanding something.

I missed that part. That's likely the cause of your issue. That mechanical cat probe is probably a couple minutes behind the actual temp, so you'd probably be ok to shut the bypass at 400, if the wood is burning well.

 

[_CY_]

those temps are way too high to be accurate .. consider verifying your cat thermometer against a digital pyrometer .. mine read 200f degree low.

my Buck 91 is set to cruise at 1,200f

 

[HotCoals]

Over time, I learned to NOT let the fire get going quite that vigorously, before engaging the cat.

I do the same. No reason to burn up a 1/4 of the wood before engaging.

 

[jdonna]

Not sure if I would worry too much about 1500 degrees? Usually if there is more air for the primary fire the cat temps will be lower, the more smoke you feed a lit cat(Air Cut) the hotter it will get. At least that is my experience with woodstock stoves.

 

[Ralphie Boy]

those temps are way too high to be accurate .. consider verifying your cat thermometer against a digital pyrometer .. mine read 200f degree low.

my Buck 91 is set to cruise at 1,200f

where do I find such a device and what's the cost?

 

[mellow]

On your Buck I think you could use the Condar Digital Cat probe, the thing to make sure of is that it is reading from the exhaust side of the cat about 2-3 inches back to get correct readings.

If not, pickup an AT-100 and a k type 2000+ thermocouple from Auberins.com, that would be around $80.

 

[_CY_]

where do I find such a device and what's the cost?

here's the latest version for $175. mine is the older version, had mine for about 5 years. I'm a tool nut .. your local HVAC supplier may have a different brand. ask for a digital pyrometer with a range to 2,000f .. http://www.check-it-electronics.com/chec06higser.html

(broken image removed)

 

[_CY_]

On your Buck I think you could use the Condar Digital Cat probe, the thing to make sure of is that it is reading from the exhaust side of the cat about 2-3 inches back to get correct readings.

If not, pickup an AT-100 and a k type 2000+ thermocouple from Auberins.com, that would be around $80.

no need for a new pyrometer if you have a way to calibrate. existing thermometer has a nut to loosen to move dial. don't assume your new pyrometer is accurate either.

probe tip is directly above cat .. when taking temp with digital pyrometer. place tip at same location. also it's nice to take a reading barely off cat so you can tell difference between cat surface temp vs air temp 2in away.