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Cracked stoves, cracked blocks, and cracked operators

Post in 'The Hearth Room - Wood Stoves and Fireplaces' started by thechimneysweep, Oct 23, 2012.

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  1. thechimneysweep

    thechimneysweep Minister of Fire

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    I suppose most folks drive cars with automatic transmissions these days, but I drive a stick. Cars with manual transmissions like mine have a device, called a tachometer, that displays the rpm of the engine. The tach has a "red zone" at the high end that tells the driver it is time to shift to a higher gear, lest he or she causes damage to the engine. Driving in the "red zone" for extended periods of time can result in a cracked block.

    Cars with automatic transmissions are designed to NEVER LINGER IN THE RED ZONE, so they usually don't have tachometers.

    Wood stoves don't have tachometers either. The problem is, wood stoves can't automatically "shift gears" to a lower draft setting when the red zone looms. The only cues for the driver of a wood stove are what can be seen through the viewing window, and the temperature of the fire.

    If you have an EPA approved stove, and both the primary and secondary flames are raging at the same time, you're in or near the red zone, and it's time to adjust the draft control to a lower setting.

    If you have a stovetop thermometer and the temperature in the center of the top plate, just in front of the flue collar, is rising into the 600-650 degree range, it is time to adjust your draft control to a lower setting.

    Wood stoves react slowly to draft adjustments, so when you "shift gears" at 650, your stove will likely peak in the 700-800 degree range, as my stove frequently does. But today's stoves are designed to withstand that brief and occasional foray, and will soon settle down to a more reasonable temperature.

    The bottom line: if you chose a wood stove that is too small, or if your climate and/or house insulation (or a myriad of other factors) creates that you need to drive your wood stove in the red zone for extended periods, you're going to eventually crack your block. There are a couple of ongoing "cracked stove" threads in this forum wherein the poster has indicated that the stove in question has been systematically overfired. If anyone is interested (Sisu? Wxman? Hogwildz?), I'll be happy to post specific examples.

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  2. My Oslo heats my home

    My Oslo heats my home Minister of Fire

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    That was well put, great analogy!
  3. rdust

    rdust Minister of Fire

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    My automatic vehicles all have tachometers, just sayin'. ;)

    Nice post though. :)

    I thought I remember reading these inserts in question have had a redesign along the way? I assume this was due to a known issues with the stoves cracking since a manufacture isn't going to change a working design just because.
  4. fossil

    fossil Accidental Moderator Staff Member

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    Good stuff, Tom...thanks! Just like other, much more complex systems, our simple woodburners have "operating envelopes". In our case we really only have to deal with one variable...temperature. Easy-peasy...but, just like any more complex system, if we continually push the system past the outside of the envelope, we are bound to eventually cause the system to fail. Rick
  5. rdust

    rdust Minister of Fire

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    To continue using the car analogy it sounds like our modern stoves could benefit from rev limiters just like our modern cars. Most cars will limit fuel or spark to keep them in acceptable/safe ranges if we should get careless for a short period of time. It would be slick if these stoves would limit secondary or primary air as required and open it back up once these settle back in. My Endeavor like to run hot due to my chimney height with the primary air closed shut, if the secondary air could have been regulated that stove would've worked much better for me.
    ditchrider likes this.
  6. Gark

    Gark Minister of Fire

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    Going with the car engine analogy; what about the old addage of "taking the big-block town car out on the highway to blow the carbon out of it" once in awhile?
    n3pro and Wildo like this.
  7. BrotherBart

    BrotherBart Hearth.com LLC Mid-Atlantic Division Staff Member

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    You are going to rue the day you did the car analogy Tom. ;lol

    The designer knows how long the exhaust pipe is going to be and has precise control of the combustion air. And a thermostat that opens and closes to maintain block temperature. And cops to control the rest.
    n3pro, rideau and pen like this.
  8. Woody Stover

    Woody Stover Minister of Fire

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    Except for thermostat stove like the BK or the old Resolute III. But you have to set the thermostat correctly...
  9. DexterDay

    DexterDay Guest

    Put a magnetic thermo on the stove top (speedo) amd probe thermo in flue (tach).

    Before stove top reaches a setpoint, I try to react to the flue. On start up or reloads. The probe rises higher and faster than my stove top.

    Great analogy. The 2 thermos are a must. IMO. The stove can be ran without them. But it would be like driving the car with no speedo and no idea of RPM.
    n3pro likes this.
  10. fossil

    fossil Accidental Moderator Staff Member

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  11. charly

    charly Guest

    Here's my tach!;lol
    100_6380.JPG
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  12. pen

    pen There are some who call me...mod. Staff Member

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    The car analogy is fun, but bogs the point down here. There is a difference between running a vehicle, or a stove, "hard", and abusing it.

    If I run my stove up to 750 degrees, I'm not causing unnecessary stress on it, that's the stress the machine is supposed to experience to do the job it was intended to do.

    The problem is, people that don't realize when they are doing something that is abusive or not. I think this comes down to a manufacturer issue where they need to be more specific in what temps constitute over firing, where to measure that from, and with what to measure that with. (essentially, give stove operators an accurate tach)

    Also, more from the manufacturers to help people understand what fuels they should be putting in their stoves, as well as what stove will suit them best.

    In the end, I'm asking for a lot of impossible things to get this system better :confused:

    pen
  13. pen

    pen There are some who call me...mod. Staff Member

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    Take it off of idle already and do a burnout Nancy :p
  14. BrotherBart

    BrotherBart Hearth.com LLC Mid-Atlantic Division Staff Member

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    At least two members here over the years have called PE and asked if burning at 900 degrees stove top would hurt the stove and were told that it would be fine. I cringed when I saw that. Keep them things down under 700 folks. And five to six works just fine if you want the thing to last.

    If that won't heat your house then you have other problems. More stoves, more insulation, a moving company or whatever.
    BrowningBAR and rideau like this.
  15. thechimneysweep

    thechimneysweep Minister of Fire

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    Pen, you do an exceptional job moderating this forum, and I respect your opinion, but I must suggest to you that this response is shooting from the hip. And not likely to get much support from any wood stove manufacturer I've ever dealt with. Your "machine" is only expected to achieve 750 deg. temperatures occasionally, for brief periods of time. Cold rolled steel and cast iron will both fail if subjected to that extreme temperature for extended periods.

    What I'm proposing here is the same thing I've recommended to my customers (including your fellow moderator BeGreen and several other forum members) for many years: that you select a stove that will heat your house on its lowest (longest burn) setting. This will ensure that you're always warm, will give you some overhead during occasional cold snaps, allow you a decent night's sleep, and extend the useful lifespan of your stove.

    I don't speak in a vacuum here: My Pacific Energy Spectrum (original design) turned 20 this month, and is still on its original (mild steel) baffle.
  16. pen

    pen There are some who call me...mod. Staff Member

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    With all due respect sweep, you saying extended periods of time is the same as them listing "overfiring is when external parts glow red"

    I have NEVER seen red on any part of my stove, even with temps on the thermo over 850 for brief times.

    The fisher that lived for nearly 30 years in this home glowed religiously (not saying that is right, but that's what it did in parts) and never had a single warp or weld issue.

    I'm putting the burdon on the manufacturers to set the redline, where to measure that, and how to do it.

    My concern is that a stove, when run too cold, will produce creosote. With a proper install, too hot should only be a stove issue, not a safety issue. If they burn too cool constantly, then suddenly get things hot, that's when the chimney goes up.

    As you mentioned, the problem often comes from folks using too small a stove, trying to do too much. In those cases of stove damage, I'm betting 750 is much lower than their actual temps and they are simply unaware.
  17. thechimneysweep

    thechimneysweep Minister of Fire

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    Pen, that recent change in PE's owner's manuals was made specifically due to a member of hearth.com, who has stated repeatedly outside this forum that he feels free to habitually run his stove so hot the flue collar "glows bright red" because that practice isn't specifically prohibited in the manual. That member has totally fried a 22-lb. stainless steel baffle, caused the area around his door to develop hairline cracks, and persisted in his habits until the repair welds opened up.
  18. pen

    pen There are some who call me...mod. Staff Member

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    And therein lies the problem. Manufacturers need to plan on the general public not knowing better, and become more specific IMO.

    pen
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  19. thechimneysweep

    thechimneysweep Minister of Fire

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    Maybe they would, if the "problem" was more prevalent. As it happens, it seems the great majority of us have the common sense not to beat our stoves to death. For example, PE sells tens of thousands of stoves every year, and the number of cracked stoves reported in any given year has never been more than six. Nonetheless, the folks at PE, whom I've come to know as fundamentally good people, figured out a way to make their stoves even more bulletproof, a design change that took 5 years to implement. At this writing, not a single one of the new-design models has cracked, even in the hands of a true abuser.
  20. BrotherBart

    BrotherBart Hearth.com LLC Mid-Atlantic Division Staff Member

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    Totally agree Pen. "If any part of the stove is glowing red" you are over firing is a cop out. By all of them. Tell them where to measure the temp and how. Or just replace the thing if it gets busted. I consider any wood stove warranty to be worth its weight in kindling. Because "Our stoves would never break. You had to have over-fired it.".

    I love Tom like a brother and respect his experience. But over firing an already cracked stove for a year 24/7, (who did they pay to hang around and keep feeding it), for a year just means it was already cracked where it was going to crack.

    And if somebody thinks they are going to talk me into heating this house with a cracked wood stove, they need to take another toke off of the crack pipe.

    Edit: Tom and I were typing at the same time. So a design change was made but they don't replace the stoves that busted before it was made?
  21. pen

    pen There are some who call me...mod. Staff Member

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    Part of me then is thankful they are so vague in their manual, and that their (or any stove company's) directions are allowing fools to help, by in home trial, create an even better stove for the masses ;lol God that's terrible, but it sounds like it's the case.

    If a stove cracks, that sucks. But if the guy was following the guidelines of the book that came with the unit, as much as I might think the person should have had more common sense in many cases, I blame the instructions he was reading. After all, those same instructions clearly told him how to safely put the unit in his home!

    pen
  22. rideau

    rideau Minister of Fire

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    Lorin at Woodstock told me to burn between 400 and 600. Said regular burning over than is hard on the cast iron.

    My stovetop thermometer indicates clearly that 750 is in the overfiring range.
  23. thechimneysweep

    thechimneysweep Minister of Fire

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    BB, I love you back, but I believe the point BeGreen was trying to make when he mentioned the ongoing laboratory abuse of the cracked stove was, the cracks have proved to be totally benign: they never grew longer, and they never opened up enough to allow any transfer of air or exhaust in either direction. In fact, if they ever did open up, it would simply add air to the conduit that feeds air to the airwash system. But the nature and location of the cracks create that they don't even do that: in no instance have the cracks proved to be more than cosmetic. And again, those cracks have only appeared in six savagely abused stoves per year, and only in stoves manufactured before 2008.
  24. thechimneysweep

    thechimneysweep Minister of Fire

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    I'm not a spokesman for PE, but it is my understanding that they are willing to replace any stove that suffers in any way with regards to performance, longevity or safety due to hairline cracking, even though every instance of said cracking they have investigated has been totally due to operator abuse. Case in point: the most outspoken forum member with a cracked stove has been authorized to receive a new stove.
  25. BrowningBAR

    BrowningBAR Minister of Fire

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    Which is precisely the reason why I went as large as I could. I was able to heat the house with the Heritage, Intrepid, and Vigilant. But, it was a pain to do so. Everything had to stay hot which resulted in awful burn times. Do I need this much firepower? No. But it sure as hell makes things a lot easier on me and the stoves.
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