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Stovepipe Temp occasionally takes off during peak of burn

Post in 'The Hearth Room - Wood Stoves and Fireplaces' started by MikeNH, Nov 27, 2012.

  1. MikeNH

    MikeNH Member

    Joined:
    Nov 27, 2012
    Messages:
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    Loc:
    Temple, NH
    Good day to you all,

    I own an Earthstove BV400C which was manufactured in 1987. This is a catalytic stove and the cat is 2 seasons old. I've been having an intermittent issue which I'm trying to resolve. First here is my setup...

    the stove is in the basement surrounded by concrete (it's inside an area that was built to be a foundation chimney jog.) There is a doublewall pipe that extends from this space, up and out the top of the chimney jog, and is attached along the side of the house. To attach the stove to the double-wall pipe, I used two black singlewall pipe 90 degree adjustable elbows, which fits perfectly between the stove and the bottom of the doublewall pipe (in an S shape). This single-wall pipe sits in a 1" lip inside the top of the stove and everything is screwed together. I have a probe thermometer in the black pipe about 10" up from the top of the stove that normally reads anywhere between 700-1000 when the cat is lit (the cat probe usually reads between 800-1200 at this point).

    Here is my problem...every so often, the temp in the stovepipe takes off...it will climb to over 1000 and keep climbing. the other day it was at 1500 and still climbing when I caught it. I opened the bypass and the stove door, which seemed to extinguish the problem and the temp dropped back down to 900. My chimney is clean and that black pipe will gather creosote now and then, but I normally clean out the whole stack monthly during a burn season. I'm trying to figure out why the pipe does this and wondering if it may be due to air leaking in at the joint between the stove and the pipe causing a burn behind the catalytic combustor and inside that pipe.

    The strangest part of this is, I've had this stove for 10 years and this only started happening - occasionally - 2 seasons ago. the only change in that time for anything with this setup is the catalytic combustor, but the cat that was in there before this one was the same style, size, manufacturer, etc, and this cat itself appears to be running normally.

    Any help would be appreciated and thank-you for your time. Please let me know if more info is needed.

    Mike

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  2. Backwoods Savage

    Backwoods Savage Minister of Fire

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    Welcome to the forum Mike.

    I'm going to bump this to the top so we make sure others get to answer it. I'm going to state right off that it sounds like you have a wood problem to start with. With a catalyst, you should have zero creosote. We've had a cat stove now for over 5 years and have yet to get creosote but we make sure our wood is very dry. We usually give the wood 3 years after being split before we burn it and that is why we don't have the problem. It also matters what kind of wood you are burning. Perhaps you've changed the type of wood you are burning? For example, if you've maybe switched to burning oak, that would cause a creosote problem if the oak has not been 3 years in the stack. Other types of wood will do fine after a year but not oak. And if there is creosote in that flue and it lights off, that could explain the climbing temperatures.

    As for that setup on the flue, I have a difficult time picturing it. Perhaps you could post some pictures?
  3. MikeNH

    MikeNH Member

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    Thanks for the reply and the warm welcome. It's good to be here. I will take a picture of the setup when I'm at home later today. This particular problem has happened maybe 4 or 5 times in the last two years, but normally at the end of the season. I don't remember the wood condition for when it happened last year, but for this year, the wood that I loaded when the issue happened was a dry mix of oak and maple. The creosote buildup was probably caused by the first month of burning this year in which I wanted to get rid of a quarter-stack of wood but I don't think it was completely seasoned. It was also a mix of oak and maple. Maybe this was a combination of the creosote buildup and the nice hot fire that got going with the first good load of dry stuff. It hasn't happened again since but I'm now at a point in my woodstack where the wood has been seasoning for 2 years. The cat has been steady at about 1200 with a nice orange glow, and the connector pipe stays steady at 700-900 during the cat burn. I'm going to install a setup similar to what others have done here on this site in order to monitor the flue temp and sound an alarm if it starts to rise. Going downstairs and seeing the flue thermometer pinned at 1600 is a little unnerving.
  4. HotCoals

    HotCoals Minister of Fire

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    Is there a gasket for the cat and is it in properly?
    There must be a by-pass on that stove..does it seal good?
    Your stack temps sound way high for a cat stove.
  5. MikeNH

    MikeNH Member

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    Hi HotCoals,

    The cat is installed correctly and it's gasketed. There is a bypass, though when it's closed its metal on metal and thus not a perfect seal. This morning I ran is with a load of 5 logs, maple and birch. During the one hour it was at its peak, the cat temp was at 1200, the flue temp was steady at just below 900.

    Backwoods Savage - I've attached a picture of how the single wall pipe attaches to the stove and to the doublewall flue. Let me know if you have any questions and thank-you both for assisting me.

    Mike

    Attached Files:

  6. MikeNH

    MikeNH Member

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    So an update, today I had some time to fiddle with this. When I reloaded it, I put in about six good, dry logs, oak and maple. Cat temp got up to 1200 as expected, but the flue temp at one point started to climb to 1200 and would have kept going. I opened the cat bypass, and the flue temp dropped back down. Closed the bypass, temp rose back up. I watched it pass 1050 and I opened the bypass again. Flue temp dropped again. I had assumed opening the bypass would have the opposite effect. I'm confused simply because we've had this stove for 10 years and didn't have this problem up until two seasons ago. Right now, 2 hours after loading that particular load, it's running steady at 1100 on the Cat (with a nice glow) and 850 on the flue. Stovetop reads 375. The way it used to run, for years, would be the cat at 1000-1500 and stovepipe at 800 during the peak of the burn like Old Faithful. What might I be doing wrong? More info if this might help, the flue is double-wall steet outside the house, about 35 feet. It's 8" all the way. The top is clean and unobstructed. Maybe this is a draft issue? Thanks again for your time guys.

    Mike
  7. Backwoods Savage

    Backwoods Savage Minister of Fire

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    Wow Mike, that looks like a mean hookup and certainly not recommended. It also does not sound like a good chimney as you need insulated. In addition, does the manufacturer recommend 8"? It does seem like the earlier models of that stove did want 8" but I'm not up to date on them at all. But if they want 6" and you have 8" that could be a problem but it does not seem so with the type of problem you have. I definitely would put part of the blame on the wood and I also wonder about that bypass as I've not known any bypass to not have a gasket. That gasket is usually located so it is difficult to see. If this is the case with the gasket, this also would explain the low stove top temperature.

    As for the excessive draft, I see a damper in that flue so it it were excessive you have the tool to tame it.
  8. MikeNH

    MikeNH Member

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    Hi Dennis,

    Thanks for your reply. I really appreciate you taking the time to help me with this. The chimney is Hart and Cooley type HT - double walled with insulation between I think. I didn't mention that in previous posts. That black stovepipe connects directly to the bottom of the chimney. The builders of the home were supposed to extend the sides of the foundation in that area higher than they did, but that didn't happen and I'm stuck with this configuration, which I never liked. It just never gave me issues until the last couple of seasons.

    You mentioned that the setup isn't recommended. I want to learn and if there's a better way I can hook this up, I'm definitely open to any suggestions if you have any.

    I have the instruction manual for this stove. It calls for an 8" flue. I also looked through the instructions for any information about a bypass gasket and found nothing, but I think parts are still available for this stove, so I can start hitting the web and look to see whether replacement parts have a gasket or not. The parts listed in the manual do not mention a damper gasket.

    Honestly what I would really love to do is buy a new stove, but we're not going to be in the financial position to do that for at least another few seasons, so I have to make this one workable and safe.

    Mike
  9. MikeNH

    MikeNH Member

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    Just an update. I found out this weekend when I spent some quality time with this stove that the baffle area in which the catalyst housing fits is cracked where its welded to the top of the stove, so I'm thinking a good portion of my issue is coming from that. this stove is 25 years old. I don't owe it anything and I can't ask much more from it. I think its time to move on. Thanks guys however, for helping me with this issue. Much appreciated.

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