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Your thoughts on ideal stack temperatures

Post in 'The Hearth Room - Wood Stoves and Fireplaces' started by Diabel, Nov 12, 2008.

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  1. Diabel

    Diabel Minister of Fire

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    Measured with magnetic exterior thermometer.

    I like to see mine at around 400*-450* anything below that I consider a less of a clean burn (of course coaling stage not considered here). Over 600* I get uncomfortable & I feel like I am wasting fuel.

    Your thoughts:

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  2. EatenByLimestone

    EatenByLimestone Minister of Fire

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    I always worry more about how the stove is running. I figure if the stove is burning all of the smoke there is nothing to worry about regarding a clean burn in the singlewall and chimney. My stack always seems to run cooler than the stove.

    Matt
  3. ikessky

    ikessky Minister of Fire

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    I thought that the temp of the magnetic thermometer needed to be doubled to find out the internal stack temp of your single wall.
  4. Jags

    Jags Moderate Moderator Staff Member

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    A surface mount thermo will read approx. half of the internal flue temp. (i.e. 450F surface = 900F internal). 900F internal flue temp is getting to the upper limits of recommended safe zones by most mfgs of stacks. Food for thought.

    Edit: 600F surface = TOO DARN HOT.
  5. HittinSteel

    HittinSteel Minister of Fire

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    I keep mine in the 300 to 400 range (single wall pipe mounted temp. gauge). I figure that is 600-800 range internally and should be enough to keep most of the creasote at bay.
  6. Wrigley

    Wrigley New Member

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    Class A chimneys are rated for 2100 degrees, right? If so, why is a 450 stack, i.e., 900 internal flue temp, too high?
  7. Jags

    Jags Moderate Moderator Staff Member

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    That is a temporary heat capacity (think chimney fire). We are talking about long term, sustained temps. All steel has a temp that they can handle before nuclear meltdown. As well as all steel has a temp that can be safely obtained and repeated through out its life time. Most mfgs. of stainless stacks advertise that safe operating temps FAR south of the 2100F. Under 1200F for any that I am aware of. If my stack gets to 1000F (internal) I start to get nervous and sure as heck wouldn't maintain that temp. Not to mention too high of temp, but thinking about all that heat being vented to the outdoors when it should be heating my home.
  8. 3fordasho

    3fordasho Feeling the Heat

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    Seems high. I have a probe type thermometer installed about 2' above the stove. I'll see 400F when charing a new load of wood,
    but once the air is cut back and cat engaged it will only run 200-250F.
  9. Diabel

    Diabel Minister of Fire

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    Yeah, with my post I was hoping to get several opinions.

    The other night for some reason the conditions must have been just right. Stove was running at around 500* but the stack for some reason spiked to 700* that 1400* internal :gulp: Needless to say it made me nervous! It stayed there for good 1.5hrs before slowly settled at 450*.

    The question is how long would the pipe last at such temperatures?
  10. Jags

    Jags Moderate Moderator Staff Member

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    Dang good question that I don't have an answer for. One things for sure, I ain't gonna be the test subject. I don't want to discover the failure point. :bug:

    There is simply no reason (other than sometimes it just happens) that a stack should be maintained at 1000F (internal) intentionally. Safety and stack concerns aside, that is simply too darn much good heat that is being exhausted to the outdoors. It is WAY above the temps needed to keep a good clean stack, and then throw the safety/ stack lifetime arguments on top of that and well.....you get the idea. Just one dudes opinion.

    Edit: Food for thought: All these mag thermos that are constantly being talked about are usually designed for surface temp of the stack. Everyone I have ever seen, has the "overfire" temp at either 500F or 550F. So there you go, by the mfg of the thermos 1000F to 1100F internal flue temp is considered and overfire. Now its not just my opinion. ;-P
  11. ikessky

    ikessky Minister of Fire

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    Since my wood furnace is not EPA rated (no cat or secondary burn), I try to make the initial fire in the morning reach ~400-450 on the magnetic gauge. I figure this helps to burn out or minimize the nastiest that may have started to accumulate with overnight burns. After I load a full load, I open the air up to char the wood nicely, and then I adjust the damper back down. It has an automatic damper that is basically a bimetal spring that opens and closes depending how much heat reaches it. If the fire is really hot I take it down in two steps because I don't want to go from wide open to closing the damper all the way. Once it is to that stage, I try to put it at a setting so that the magnetic guage reads ~200-250 (roughly 400-500 interal temp).
  12. Diabel

    Diabel Minister of Fire

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    Jags,

    I appreciate your opinion. I strive to run mine at 900* internal & your opinion is, that it is too high....I am wasting fuel!!! At 600* internal I will likely get a stall & smoke.
  13. Jags

    Jags Moderate Moderator Staff Member

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    WOW! you really gotta run that high just to keep the stove operating? Not doubting you, but that seems like a high temp to maintain. Do you go through what you would consider a high volume of wood for the heat produced for your home?? These are honest questions, like I say, I learn something new every darn day I am on this site.
  14. 3fordasho

    3fordasho Feeling the Heat

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    I think it maybe quite useless to compare flue temps as there is much variation in these cheapy surfacemount thermometers. I've compared the woodstock thermometer that came with the stove to a rutland version (both on the stovetop) and seen 100-150F differences. (FWIW the woodstock supplied unit seems closer). Then throw some of these on the flue, now are we talking single wall or double wall? To make matters worse, I had one on double wall pipe, but it was an adjustable section so it actually had 4 layers of sheet. I've heard the inside temp will be double the reading on the outside of the pipe, but again is this for single wall or double wall? I thought I would get accurate flue temps with Condors probe type thermometer, but that read way off because its not a true probe thermometer with the coil in the probe, and the 4 layers of material in my adjustable section of pipe threw it way way off. I currently have a teltru industrial process probe type that has the coil in the probe, I think I am getting accurate readings- just have to be careful and not exceed 800F with it, that can damage the coil (measuring element) in the probe. It is a 200-1000f range unit, +/-1% full scale accuracy. 800-1000F intermittent use ony.
  15. Jags

    Jags Moderate Moderator Staff Member

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    This discussion has all been concerning single wall pipe.
  16. trailblaze

    trailblaze New Member

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    i get mine up to approx 400 degrees (this is also when my stove top hits 550ish) with the damper open and air at 50%.....

    once i get a nice coal bed, i shut the damper and the temp drops to 300-325ish.... when the wood is mostly burned out (5-7hrs) the temp is 250 ish and falling...

    this is with a DW non-cat stove
  17. Diabel

    Diabel Minister of Fire

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    I don't think I burn more than others with similar stoves (2.1 box), but than again what do I know :)

    I load every 6-8hrs depending how cold it is outside, two three splits of hardwood.
  18. Jags

    Jags Moderate Moderator Staff Member

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    That doesn't sound out of place. Hmmm...
  19. Diabel

    Diabel Minister of Fire

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    Yeah, I don't think I am out of place in terms of fuel quantity burnt.
  20. Jags

    Jags Moderate Moderator Staff Member

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    Have you checked your thermo for accuracy?
  21. mikeathens

    mikeathens New Member

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    Did you have a loud rumbling coming from your stove? That's one of the reasons I got rid of my DW NC. It seemed to go into "meltdown mode" for no apparent reason. Like 800*-900* on my surface thermometer. I don't know if it actually helped or not, but you might want to make sure you have a GOOD seal between your flue collar and connector pipe. I actually used gasket cement in mine. The instances of meltdown appeared to be reduced, but I didn't have the stove too much longer to be certain. Those temperatures you have seem a bit high to me. But what do I know... :roll:

    On my Mansfield, I let my stack internal probe thermometer get up to 600-700 before I knock the primary air back. It will hover at 600 or so for a while before dropping back to 400. ~400 is exactly where I like to keep it - I know secondary is working well, and the stove is at a nice temperature (400-500). I keep the primary open more if I want the stove above 500. I have only let the probe temp. get above 700 a couple of time. Usually attributed to beer.
  22. Todd

    Todd Minister of Fire

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    My single wall external temps are 200-250 low burn and 250-300 on higher burns. Stove top temps read 450-650. When I have the bypass open the temps are much higher. They were about 100 degrees higher last year before I installed a pipe damper. My thermometer is a Woodstock and is very close according to an oven test. I've had Rutland and others and they all seemed to read hotter. My stack thermometer is 18" above the flue collar.

    I remember those everburn stoves were reading very high stack temps in all those other threads last year and I think it was due to the afterburner in the rear of the stove. It seems most non cats run a little hotter stack temps probably because they need those higher temps to get that secondary burn?
  23. Todd

    Todd Minister of Fire

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    For chits and giggles could you put your external next to your internal and see what the diff is? I find it hard to believe your running 200-250 internal unless it towards the end of the burn. A while ago I asked Woodstock for some internal temp info and they told me they have an internal probe 6' up that reads 400 on a full load.
  24. mikeathens

    mikeathens New Member

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    Todd, I remember my DW Cat running really low flue temps with the cat engaged...it's been so long ago. I don't know if they were that low, but a lot lower than my non-cat, for sure.
  25. Diabel

    Diabel Minister of Fire

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    That does not sound right 200-250 internal that's 100-125 external unless the 1/2 formula goes out to lunch at this stage of the burn.

    Right now my stack (external magnetic) reads 200* stove top (griddle) 450*...this is 4.5hrs into the burn, (coaling stage & light load). These downdraft stove definitely have to run at much higher stack temps vs cat stoves or burn tubes stoves.
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