AAARG! Another Cracked Combustor!

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Todd

Minister of Fire
Nov 19, 2005
10,323
NW Wisconsin
It happened again. Some of you may remember a couple years back my cat had this problem and I figured it was from some kind of thermo shock from wet wood or engaging the combustor too soon. Well the last couple years I was very careful about dry wood and giving it proper time to engage. Everything seemed fine til yesterday when I did my spring sweep and inspection. The cat is cracked just about everywhere and there is a little crumbing or broken pieces, but not too bad yet.

I gave Woodstock a call. They have been keeping notes on me since I bought the stove. I think thats good, they can help troubleshoot. How can this be, I ask? Wood moisture is 20% or less and I always give 10-20 minutes before engaging the cat. After a good long discussion on how, what ,where, why,and when, they came to the conclusion it has to be overdrafting and recommend a pipe damper. They say my internal flue temps of 600-800 are too high and you could be sucking flames into the cat causing it to crack? What? 600-800 is the normal range for my internal probe, I thought cracking was from thermo shock, but they say flame impingement also causes cracking.

I don't know, I'm a little puzzled and upset. Chimney is 25' from top of the stove, outside wall brick chimney with 5.5" stainless liner. Wouldn't one think if I'm overdrafting I'd be close to overfiring too. Not so, I've been over 700 only a couple times and brought it back down quickly. The stove always seems under control and I don't have a roaring stream of flame going up into the cat. Since the cat is waranteed for 3 years, they are sending a new cat free of charge again, and I'm going to install the pipe damper for next season and see what happens. I wonder how many time they will let me go on this til they charge me for replacement. If it were me on the other end, I'd be thinking this guys burning wet wood and overfiring his stove. They seem to have great patience.
 
I really doubt it is some wet wood or anything like that.

Is this cat "canned" - meaning is it ringed with stainless steel and a gasket?

Cats crack - that can happen in a week, month or year - but they usually hold together and therefore do the job. In other words, cracks in themselves do not mean a lot. Only when large chunks fall out would there be a major problem.

Yes, a pipe or baro damper might just less flame impingement and therefore less shock.
 
Todd, my stack temps are nowhere near what yours are. We don't have a probe but just a magnetic thermometer on the horizontal section of black pipe and except when reloading, that temperature is usually around 300 degrees max.
 
Definitely put a pipe damper on that thing. My basement chimney is a 5.5 just like yours pulled through the thimble. With the damper wide open a couple of days ago I could hold the stove door a half inch away from closed with a fire burning and it would slam shut when I let go of it. On a 60 degree day!

Methinks those 5.5s get hotter and crank up a bunch of velocity. If mine was insulated I would have to put rocks on top of the splits. I can watch it sucking ash up the pipe when it is burning. It isn't hard to imagine yours pulling flame into the cat.
 
Webmaster said:
I really doubt it is some wet wood or anything like that.

Is this cat "canned" - meaning is it ringed with stainless steel and a gasket?

Cats crack - that can happen in a week, month or year - but they usually hold together and therefore do the job. In other words, cracks in themselves do not mean a lot. Only when large chunks fall out would there be a major problem.

Yes, a pipe or baro damper might just less flame impingement and therefore less shock.

Yes, it has a gasket and is incased in a iron frame. This thing has cracks everywhere going all the way to the other side, almost every honeycomb. Some of those honeycombs are falling apart where there should be 3 or 4 separate honeycombs there is one big one. I was told they usually don't start to crack til the end of their life.
 
Backwoods Savage said:
Todd, my stack temps are nowhere near what yours are. We don't have a probe but just a magnetic thermometer on the horizontal section of black pipe and except when reloading, that temperature is usually around 300 degrees max.

With an external magnetic thermometer I was running anywhere from 250-400. I installed a probe this year just to get a better idea what the internal temps were. I figure if it's over 500 in the pipe the cat has to be working.
 
Todd we have compared #'s before, and I always thought that your probe temps being higher than stovetop were weird. I kinda thought it was do to the soapstone. My probe temps are always lower than stovetop (when cruising) but then againI burn a totally different animal.
 
BrotherBart said:
Definitely put a pipe damper on that thing. My basement chimney is a 5.5 just like yours pulled through the thimble. With the damper wide open a couple of days ago I could hold the stove door a half inch away from closed with a fire burning and it would slam shut when I let go of it. On a 60 degree day!

Methinks those 5.5s get hotter and crank up a bunch of velocity. If mine was insulated I would have to put rocks on top of the splits. I can watch it sucking ash up the pipe when it is burning. It isn't hard to imagine yours pulling flame into the cat.

I think your right BB, Same thing has happened to me with my loading door. I just finished installing the damper and while I was, I lit a match and stuck it next to the crock and it blew it out! Not that I really want one but the wife says I can't buy another stove so I hope this is the fix.
 
Gunner said:
Todd we have compared #'s before, and I always thought that your probe temps being higher than stovetop were weird. I kinda thought it was do to the soapstone. My probe temps are always lower than stovetop (when cruising) but then againI burn a totally different animal.

Yea, I remember. My external pipe temps were always lower than my stove top (when cruising) but since I installed the probe they cruise at 600-800 when the stove top is 500-600. I thought that was a normal reading, thinking the internal was a little over twice the temp of the external? What are your temps?
 
INTERNAL PROBE 18" from collar is almost always 200deg lower than stovetop at cruising... 400probe is 600 stopvetop.

If you are getting good long burns, have good control over the fire, and no runaway temps how are you overfirng?

Is the flame contact theory suppost to be from when cat is not engaged and you are charring a new load or when the cat is engaged and you have those nice lazy flame?
 
Gunner said:
INTERNAL PROBE 18" from collar is almost always 200deg lower than stovetop at cruising... 400probe is 600 stopvetop.

If you are getting good long burns, have good control over the fire, and no runaway temps how are you overfirng?

Is the flame contact theory suppost to be from when cat is not engaged and you are charring a new load or when the cat is engaged and you have those nice lazy flame?

I don't know, I'm scratching my head on this one. The only thing I can think of is when I engage there is alot of flame for a few minutes then it settles down to that low lazy burn. Maybe the draft is really rippin before engaging and I should slow it down some before engaging? But when I look up at the cat after engaging I don't see any flames hitting the cat, they kind of disperse at that protection screen.
 
While my stove is a non cat I do have a probe installed 18" above the collar and during intial fire build up my stove will hit a stack temp pretty easily to 800 and a couple of time I walked away for a few minutes with the dampner open (installed above the probe) and have hit probe temps around 1,100. Close the dampner down elminates the high probe temps.

I have also after having an established large coal bed on refueling the stove without raking coals forward to the glass had fully dampned stove controls and open dampner (pipe) and can easily hit 800 plus, so I dampen down the pipe as well.

You need a dampner in place for sure from what I have read.

I brushed my liner on Sunday and put a grocery plastic bag over the pipe and it almost sucked the bag into the pipe.
 
Struggle,
So when your cruising along at 500 stove top what kind of internal pipe temps do you shoot for?
 
Once the fire has settled it will drop around 400 and be fully dampned down both pipe and stove it will cruise around 400.

Getting to the 500 degrees though it will maintain 600 stack temp with the pipe dampner closed half way. If I dampen everything down to fast it will kill the fire.
 
Thanks guys, I'm definitly running too hot then. I installed a pipe damper yesterday.
 
Todd, I think I remember Tom (Sweep) mentioning the percentage difference between 5.5 and 6" pipe and it was signifiacant so I think BB's got a great point. I'm off in the opposite direction with a flue that's abit bigger than optimum. In regards to stack temp vs stove top, seems to me the Woodstocks have a couple of differences from other stoves. The first being that it's a cat and the combustor can get mighty hot even when the firebox isn't all that warm. The second is the insulating air layer between the double wall soapstone in the Woodstock construction. Between the two, it seems feasible to me that your stack temps would run hotter than the stove top in your Fireview. It's my experience with my Keystone that when my external stack temp is 275+ and rising, I'm good to go in engaging the cat even if my stove top is under 250. Don't have a probe but my impression is that my flue gas temps may be close to twice the external reading. Haven't pulled my cat out in a couple of months but it sure is firing good. Could be all chewed up for all I know but I don't think so. Craig's comments about cracks etc agree with my understanding too. Gotta like Woodstocks customer service, sending you new cats for free and all.
 
jpl1nh said:
Todd, I think I remember Tom (Sweep) mentioning the percentage difference between 5.5 and 6" pipe and it was signifiacant so I think BB's got a great point. I'm off in the opposite direction with a flue that's abit bigger than optimum. In regards to stack temp vs stove top, seems to me the Woodstocks have a couple of differences from other stoves. The first being that it's a cat and the combustor can get mighty hot even when the firebox isn't all that warm. The second is the insulating air layer between the double wall soapstone in the Woodstock construction. Between the two, it seems feasible to me that your stack temps would run hotter than the stove top in your Fireview. It's my experience with my Keystone that when my external stack temp is 275+ and rising, I'm good to go in engaging the cat even if my stove top is under 250. Don't have a probe but my impression is that my flue gas temps may be close to twice the external reading. Haven't pulled my cat out in a couple of months but it sure is firing good. Could be all chewed up for all I know but I don't think so. Craig's comments about cracks etc agree with my understanding too. Gotta like Woodstocks customer service, sending you new cats for free and all.

My external pipe temps use to run about 275-400 with stove tops of 500-650. Now the internal pipe temps run 600-800. I just figured the internal temps were double the external? Woodstock told me the internal temps are too high and I should be running a 300 external. They never told me what internal temps to run, wonder why, I should of asked. Next time I burn I'll double check the internal/external temps and see what the exact diffrences are. This is giving me a headache.

I'm thinking the problem is a combination from the 5.5" liner and me engaging while that draft is sucking too hard. I'm going to have to watch the pipe temps a little closer and give it less air when egaging. Also think the pipe damper will help some.
 
Yeah, it will be interesting to see how the damper affects this for you. I've always thought it might help if my draft was better, now I'm wondering if it's better that it's not!.. The season's just about over too. Guess we'll have to wait til next year to find out huh?
 
Todd: or you could just buy one of those big 3.1 cu.ft bears and give it a big hug. You know, the bear with the kodiak steel disguised as fur. :coolsmirk:
 
sonnyinbc said:
Todd: or you could just buy one of those big 3.1 cu.ft bears and give it a big hug. You know, the bear with the kodiak steel disguised as fur. :coolsmirk:

Ha, Ha, the wife won't let me buy another stove. She loves the Woodstock look. Me on the other hand would love to have about 3 or 4 different stoves and change them out every so often. So many good stoves out there and so little time to burn them all. If only Woodstock made a 3cu ft, downdraft, cat, burn tube, soapstone, cast iron, toploading, EBT stove, i could die a happy man. :lol:
 
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