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Yikes; temperature of CAT probe hitting 2000 degrees!

Post in 'The Hearth Room - Wood Stoves and Fireplaces' started by Gridlock, Mar 24, 2010.

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  1. Gridlock

    Gridlock Member

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    For the second time (that I know of) the temperature of the CAT probe hit 2000 degrees. I was in bed reading last night and started hearing an unusual number of metal pinging expansion sounds when I noticed what the CAT probe was reading. I also smelled some non-wood burning, and noticed the CAT combustor glowing very brightly, so immediately opened the damper to cool down the CAT and burn down the wood somewhat. After re-engaging the CAT, the temperature was hovering around 1,750 when I went back to bed.

    I am using a Candor digitital gauge (http://www.condar.com/digital_monitor_woodstoves.html) and have heard that it may read 200-300 degrees high, which would still be quite hot. The manual for my stove mentions that normal CAT operating temperature should be between 1000 and 1700.

    Why did the temperature go up so high? I noticed that there was very little flame, just the hot coals at the bottom and some charred wood. Would wood that is wet or not well seasoned cause a lot of smoke which can cause the CAT to work hard raising it's temperature? How do I deal with this once it happens? Does increasing the air control cause more or less smoke? Lowering it seems to make sense since it would cause the wood to smolder more; but raising it also makes sense since more combustion = more smoke. What do you think?

    Thanks

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  2. REF1

    REF1 Feeling the Heat

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    I don't know that a cat in the circumstance you describe is working hard, as it is working very well, and you just have to keep the air intake closed a little more. Cats love smoke and volatile gases. Your load was producing them, so the cat was burning them and getting hotter as a result. Just back off your intake to reduce overnight combustion a little in the same load circumstances.
  3. Gridlock

    Gridlock Member

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    I had the air intake almost closed completely when this happened, which I thought may have been contributing to the problem since I thought it may cause more smoldering. The slight burning smell also worried me and the fact that VC suggests not running the CAT temperature above 1700 degrees.
  4. REF1

    REF1 Feeling the Heat

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    Sounds like you were smelling hot iron. A very distinct odor, hot iron and steel. The very fact that VC recommends not running the cat above 1700 (common recommendation) shows that the cat can exceed that temp fairly easily. If the load was down to coals and charred wood, it seems odd the cat would be that high, but if you heard the expansion of metal and smelled the odor of hot metal it is unlikely the thermometer was reading improperly. As long as the stove wasn't glowing, itself, it may be your cat goes through such a cycle regularly and you just sleep through it every night?
  5. Gridlock

    Gridlock Member

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    Yes, it's entirely possible, though I noticed that this time there was almost no flame unlike most times before going to bed when I noticed at least some flame. Only the outside of the wood was charred; I had filled the stove almost completely on top of a nice bed of coals, let it burn for about 15 minutes wide open, then engaged the CAT, at which point the CAT probe temperature rose until it hit 2000 degrees (which took about 30 minutes after engaging). By the way, the stove top griddle temperature was reading only about 400 degrees at the point the CAT probe read 2000.
  6. REF1

    REF1 Feeling the Heat

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    Oh, so you witnessed the cat hitting 2000. You went to bed with the cat running at that temp? Yikes. I'd respect the thermometers reading and not count on it being a few hundred degrees off and either not load so much, or shut it down even more, or install a damper in your stove pipe. I had to do that with my cat Elm years ago. I'd shut the air intake down to the thickness of a framing nail and the cat would still rise above where I wanted it, so I installed a damper in the flue above the stove and that helped control strong draft quite a bit and calmed down the combustor. I just had to find the right angle to set the damper to do the job and not snuff things out.
  7. grommal

    grommal Feeling the Heat

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    Not sure if your Defiant works like my old Defiant Encore did, but on that stove the air intake had a bimetallic thermostat. The bimetallic element was located in the side of the stove near the air intake handle, so it was tweaking the incoming air based on firebox temperature. So, with a fairly cool firebox like the one you describe, it would open the air more even if I had it pretty much shut down, regardless of the cat behavior.

    The flip side was also true, where it would choke off the input air even if I wanted to let more in to get out of a backpuffing situation.
  8. Gridlock

    Gridlock Member

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    Well, when I went to bed I had just closed the damper, and the temperature was not that high. I only noticed something was going on when I heard a lot of metal expansion noises and smelled a bit of burning. Thanks for the info about the pipe damper; I'll check with the folks that installed the stove.
  9. Gridlock

    Gridlock Member

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    Interesting, I hadn't thought of that. That does certainly seem it could explain what happened. The stovetop temperature was definitely lower that it is normally when running with the damper closed with a full load of wood. It would make sense that the thermostat opened the air intake more which could have resulted in more smoke generated, therefore high CAT temperatures.

    I'm not quite sure what the value is of a thermostatically controlled air intake.
  10. hothead

    hothead New Member

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    Are you saying that your cat probe was reading 2000 degrees (coupled with a burning metal smell) and that NO part of the stove was glowing? That seems unbelievable...My stove (Lopi Leyden) will behave very similar to your stove. If I have a good coal bed and load the stove with wood and close the intake down, the wood will char black and the back of stove (where the combustor is located) will glow red. The griddle top only registers about 500 degrees because it's somewhat insulated from the coal bed and is not being hit with a direct flame. I am not experimenting with a flue damper to see if that helps.
  11. Gridlock

    Gridlock Member

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    The only part of the stove I noticed that was glowing was the CAT combustor; I didn't see any metal part glowing, but the area around the combustor could have been obstructed by the wood in the stove, and I didn't look behind the stove (the back is also somewhat blocked from view by the rear heat shield). I did not notice any outside part of the stove that was glowing.

    I assume you mean you are NOW (as opposed to NOT) experimenting with a flue damper? Do you know what the temperature is in the combustor chamber when the combustor is glowing?
  12. slindo

    slindo Member

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    Can you really see your cat when the stove is burning? That sure would be handy.

    Don't know about your stove, but the older VC cat stoves like our Defiant Encore have a separate air intake just for the secondary cat combustion, with its own thermostat to regulate how hot it gets. The thermostats burn out fairly regularly, usually this leaves them in the closed position. But if one managed to jam in the open position it could cause unusually high secondary combustion temps. The cat is also in a refractory box, which pretty much insulates the outside of the stove from the secondary burn heat, so it could get awful hot without the outer iron showing it.
  13. hothead

    hothead New Member

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    Sorry, I meant to type "now" instead of "not". I just installed the damper and haven't used the stove in the last two weeks. Unfortunately, I have no idea what the actual temp of the combustor is, but the cast iron enclosure surrounding the combustor glows red. The first area to start glowing red is near the output ports of the combustor. Eventually, the entire back will start to glow (from orange to light red) if I load up the box with wood. The rear heat shield does block the view somewhat but if you look down along the side you may be able to see it (it helps to turn off the lights in the room to see the glow). I am not happy about having to use a flue damper, but I need to be able to sleep at night without fear of my stove melting down...
  14. fbelec

    fbelec Minister of Fire

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    i was hoping some of the people from other threads would chime in. i don't have a cat stove but i read on an thread or two here that if you choke down the primary air to much you'll make more smoke for the combuster to fire. so if your combuster is running to hot open the air a little for more flame and less smoke for the combuster to burn. it sounded weird to me also but it makes sense in a way. calling all vet cat stove burners.
  15. fire_man

    fire_man Minister of Fire

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    This is exactly what I do when my Cat temperature starts to climb way too high. The only times I see excessive Cat temps is when I have choked back the air supply for a long burn and there is no visible flame in the firebox. I think what happens is the Cat is getting stuffed with tons of smoke and as soon as I open the air supply and get a little flame going some of that smoke gets consumed in the firebox before entering the Cat, thus reducing its food supply and temperature. It's a little backwards, but more air means lower cat temps. That's my take on it.
  16. Mandoo

    Mandoo Member

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    +1

    The only time I get too high of a cat temp is with it choked down and too much smoke. Don't close the primary all the way with a full load of charred wood. I usually nudge it to 1/2 3/4 closed.

    Heck of a heater isn't it? Just don't make the stainless cat mistake I did! Going back to ceramic.
  17. Gridlock

    Gridlock Member

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    Yes, I can see the CAT through the holes in the throat (a piece of iron which protects the CAT from direct flame). I don't know about a secondary thermostat; it may be there but I haven't seen it; I'll need to look into this, thanks.
  18. Gridlock

    Gridlock Member

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    Yeah, I understand your worry about this. If this happens again (or when the combustor gets to the high end of its normal temperature operating range, I'll take a peek inside the heat shield to see if anything is glowing.
  19. Gridlock

    Gridlock Member

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    I spoke to the sweep earlier today who installed the stove, and he mentioned this exactly. Reducing the air supply creates more smoke which can over-work the combustor, if there is a lot of wood in the box (which there was) and the air is choked down too much. In my case I believe the situation was exacerbated by the fact that I didn't burn the wood long enough when I packed it, so the firebox wasn't hot enough, thereby producing a lot of smoldering smoke.
  20. Gridlock

    Gridlock Member

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    Yep, that does seem to be the consensus!
  21. Gridlock

    Gridlock Member

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    +2 for chocking down the air too much with too much wood.

    Yes, it is a heck of a heater! I'm amazed at how much heat it produces for such a long period. And it looks great too!
  22. Gark

    Gark Minister of Fire

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    Our Encore CAT 2550 does the same thing (overfire the CAT) when too many logs are hot enough to outgas at once and then close the damper. The cat eats too much smoke and gets way hot.
    The Encore is a smaller version of your 1945. Why torch all your fuel before closing the damper when your manual states:
    "NOTE: If the remaining charcoal bed is relatively thick and if your fuel is well seasoned, it is possible to add fresh fuel (smaller pieces first), close the door and damper, and reset the primary air thermostat for the desired heat output."
    (see page 23 of your user manual).
    Also, you can shove most of your coals to the far left (or right) of the firebox before loading those 22 inch logs (tightly packed -no spaces between logs). This will make the fuel load burn from one end to the other end- like a candle. So on a bed of coals:
    1. Shove all/most of the coals to the east or west end of the firebox.
    2. Load 'er up with 22" logs, tightly spaced, no gaps between sticks.
    3. Close the damper and set your primary intake to where it will cruise all night.
    This method requires proper timing. The coal bed has to be down to where coals shoved to one side are 3" deep before reloading.
    You bypass the charring of a new fuel load and don't overfire your cat. It's how we get a long even burn from our Encore 2550 cat.
  23. hoverp

    hoverp New Member

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    Sorry for the partial hijack, but what is wrong with your stainless CAT? I love mine in the BK Ultra.
  24. Mandoo

    Mandoo Member

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    [/quote]

    +1

    The only time I get too high of a cat temp is with it choked down and too much smoke. Don't close the primary all the way with a full load of charred wood. I usually nudge it to 1/2 3/4 closed.

    Heck of a heater isn't it? Just don't make the stainless cat mistake I did! Going back to ceramic.[/quote]



    Sorry for the partial hijack, but what is wrong with your stainless CAT? I love mine in the BK Ultra.[/quote]





    All was fine and the last three weeks it started to give us problems. I pulled it out and sure enough it was partially clogged and warped like the others. A few referenced this problem in different threads.

    I'm not too sure what it's clogged with I tapped it ever so gently brushed it with a soft brush and blew through it. Still partially clogged but it does light off and perform ok with a hot stove. If it wasn't distorted I'd give it another chance. Here is one of the threads.

    Stainless Cat Problem
  25. Gridlock

    Gridlock Member

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    Thanks much for the info and suggestion. So it seems based on your technique, that you are relying mostly on the CAT to produce heat, since if you aren't lighting up the wood on a new load, you aren't going to get much direct heat from it. I also wonder if this will produce an excessive amount of smoke, since the firebox may not be hot enough to burn a lot if it on its own, relying almost completely on the CAT. Then again, if you aren't charring all the wood, I suppose not much of it will be producing smoke at once.

    Anyhow, it's certainly an interesting idea and I will try it later. By the way I think I hit a record last night: I briefly noticed 2100 degrees on the CAT thermometer and 750 degrees stove top at the same time... yikes!!
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