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Flue temp - stove top temp ?

Post in 'The Hearth Room - Wood Stoves and Fireplaces' started by Billybonfire, Oct 15, 2012.

  1. David Tackett

    David Tackett Member

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    My stove hangs around 300 on pipe and 500 on top.
    Billybonfire likes this.

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  2. swagler85

    swagler85 Minister of Fire

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    Question on the stove top reading, are you getting the reading directly on top of the stove or on the flue right where the pipe exits the stove? Also on the flue how high up are you checking the temps?
    Thanks
  3. Billybonfire

    Billybonfire Feeling the Heat

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    Morning Swagler,
    I normally leave the thermo on the pipe about a foot above the stove, generally reads between 300f-500f, down to 200f when coals an then I reaload.
    Was just curious as to differences between stovetop temps and pipe temps.

    regards

    Billy.
  4. swagler85

    swagler85 Minister of Fire

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    Ok thanks, last year was my first year burning and I didn't run a thermo. I bought one this year and want to make sure I'm doing it right.
    Thanks
    Billybonfire likes this.
  5. remkel

    remkel Minister of Fire

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    Check your stove manual on stove top thermometer placement. My stove recommends one of the four corners. I placed it on the corner that is consistently the highest temp.

    Each stove may recommend a different location. On the flue, 12-18 inches up should do.
    Billybonfire likes this.
  6. joecool85

    joecool85 Minister of Fire

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    That's where we let our stove cruise. Below 350F or so and it isn't burning that clean, above 650F and it will cook you out of the house...plus it seems when you get in that range it's a bit unwieldy and very easy for it to keep climbing. I've had our 17-VL up to 750F or so before, no glowing but it was a pucker moment and boy did the living room get hot! It was 15F or so outside and 92F inside....
  7. Jclout

    Jclout Member

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    Why is it that the secondaries took off when the stove top was 400 and then the air shut down?
  8. Ryan Clark

    Ryan Clark New Member

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    I took bits of info from the good folks on here and tried to find what worked better than what i was already doing. 400 is a good hot point where moisture has been cooked off and char is forming. Air goes down slowly and the gases build up from less flame. The secondary burn takes care of the gases and puts more heat in the box and less up the flue. Huntingdog and Backwoods Savage gave me lots of advice on this. Correct me if I'm wrong guys, but thanks!
  9. Jclout

    Jclout Member

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    So the burn is clean and more efficient in putting heat in the room than when the primary air is open more because it is naturally sending more heat up the chimney? Are you actually getting more heat from the secondaries alone with less air rather than - more air, more flame on the wood, and secondaries burning? I will try this with my Quad, thanks Ryan
  10. rideau

    rideau Minister of Fire

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    Shutting the air down makes the smoke travel out of the stove more slowly, gives the stove more time to burn the gases, the burning gases (secondaries) give off lots of heat. Draft higher, less time in stove, less gases burn, fewer secondary flames, less heat.
    Ryan Clark likes this.
  11. corey21

    corey21 Minister of Fire

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    I have found that if i wait till 400 stove top then close the air half way the smoke starts burning then at 500 i close it to just barely open and i get a nice secondary burn and no smoke out the chimney.
  12. Huntindog1

    Huntindog1 Minister of Fire

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    Well thats a complicated question, your asking what ratio of wood burning flames to secondary flames in the top is the best heat output. Well I think you can get alot of heat out of these stoves no problem with good dry wood. I think people usually have a big enough stove to get the heat out of them. There are a few people using under sized stoves. The thing most people are trying to do is to get longer burns for over night burns so they dont way up or dont come home from work to a cold house.

    What that is all about is getting the stove heated up to the point you can start shutting the air down to get the stove in the secondary flame mode. If getting the heat up in the stove takes too long as you have low quality wood then alot of your wood load , you loaded for a all night burn will be used to get the stove up to temps to get it shut back down. The quicker the heat comes up in the stove the quicker you can shut the stove back down, dry wood helps alot in this process as when guys say use wood thats been cut stack split for 2 to 3 years thats why they say that.

    Look up rake your coals forward as its a technique used to get the hot coals to the front of the stove so you can load a majority of the wood in the back of the stove not on hot coals thats the wood that starts to burn more slowly while you can load small kindling in the front on those hot coals that will very quickly get the stoves temps up to levels for secondary burn. This is specially important if your wood is not the best but usable.
    Billybonfire, Joful and Ryan Clark like this.
  13. Huntindog1

    Huntindog1 Minister of Fire

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    The stove has a certain amount of draft or suction pulling air into the stove thru the openings primary air, dog house air and secondary air inputs. By closing the primary air the ratios change if less air is coming from the closed primary ports then more air is being pulled into the secondary input holes.
    corey21 likes this.
  14. Jclout

    Jclout Member

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    Alright so if there is more air being fed to the secondaries it must increase the amount of heat you get from them right? Also why does waiting till the wood to be charred matter (from other stuff I've read) and how much of that load should be charred before you start to close down, just the splits in the very front of an E/W load? This is great info by the way, thanks guys! I don't think I've ever run my stove most efficiently, I hope I can change that this year, if it ever gets cold enough.
  15. Mo Par

    Mo Par Member

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    If I really crank up the Fisher the top reads 700, stack 400 (measured at the top of the elbow before entering the chimney). I usually try to keep the top around 4 - 500 and the stack 300 or so.
  16. DianeB

    DianeB Feeling the Heat

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    the manual for my stove (Jotul Castine) says once the stove has reached a surface temperature of 400-600, adjust the primary air control lever as necessary to generate heat output and burn time desired" I read that to mean the mfg. does not want the stove to exceed 600. I am sure there is some engineering safety net, perhaps to 700 but as a rule, don't go there. My manual shows me where to place stove top thermometer.
    The thermometer I use was made by Condar and it says between 400-600 range is "best zone" creosote range is 100 to 400 and too hot zone is over 600 to 900. I guess off the chart over 900.

    I bought 2 therm. to put them on the stove top to the right and left to make sure both sides burning the same way...in the beginning wanted to make sure the door gaskets were tight
  17. BrotherBart

    BrotherBart Hearth.com LLC Mid-Atlantic Division Staff Member

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    I have never had a clue what the flue temp is. The stove top is what I am interested in. If the wood is dry and the flames are at work the pipe is gonna be fine. The pipe was tested at 1,000 degrees continuous. The stove wasn't.
  18. corey21

    corey21 Minister of Fire

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    Correct me if i'm wrong but stove top temp is useful as to know when to make air adjustment and if i take care of that the pipes will be fin?
  19. Joful

    Joful Minister of Fire

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    I could not add anything to Huntingdog's excellent post, but perhaps to simplify what he's saying... given a fixed set of draft conditions and how you stack it in the stove, the wood is going to burn at a certain rate, with your only control over that being your primary air control [1]. When you have the primary air control open wide, most of the gasses generated by burning the wood are being consumed/burned directly in the firebox, and although you're sending a lot of air volume through the secondary system, there's not much flammable material left in the exhaust for it to re-burn. More heat goes up the chimney in this state, simply because of the velocity at which you're moving air thru the system.

    When you close down on the primary air control, two things happen: (1) system velocity decreases, and so less heat goes in the chimney, and (2) firebox temperature drops, and so less of the exhaust gasses are burned directly in the firebox. This is where the secondary system will "take off", so to speak, now burning the exhaust gasses generated (but not burned) in the firebox. In this mode, you are still producing some heat from the firebox, but perhaps more from the secondary system doing its re-burn.

    As to which mode produces more heat, there's probably a happy medium where both are working in unison -- which varies from installation to installation, and depending on weather and draft conditions. You are correct that it is more efficient to burn slower, in that you're throwing less heat up the chimney, but running WOT [2] may actually be the mode in which you are "getting more heat" out of the stove. In other words, your stove has two potential heat sources, the firebox and the secondary system, and your primary air control is your mixing valve, controlling how much work each of those two systems is doing.

    [1] - in the absence of a flue damper or manually blocking off your secondary air inlets.
    [2] - WOT = Wide Open Throttle
  20. rideau

    rideau Minister of Fire

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    Great simple clear description.

    I would only add a footnote that "getting more heat" out of the stove, = getting more heat per hour, but a shorter burn cycle.
    Ryan Clark likes this.
  21. Woody Stover

    Woody Stover Minister of Fire

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    I've got a thermo lying on the horizontal (stainless) tee snout, maybe 6" behind the flue collar. I saw the pipe start to glow faintly once when that thermo was approaching 800 surface which from what I understand would be over 1000 internal. I don't want to see anything glowing in my setup so if I start with the air full open, I am cutting back the air fairly soon, maybe within a few minutes. I'm not in that big a hurry to get the stove up to temp so I ramp up the temp moderately, never with full air except at the very beginning. My goal is to avoid unnecessary stress on the stove or the flue pipe. Since my stove top lags so far behind flue temp, I like to use thermos on both.
  22. Jclout

    Jclout Member

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    Thanks for the explination Joful
  23. bag of hammers

    bag of hammers Minister of Fire

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    The experiences in this thread are a great help - overall in general I'm kinda leaning towards "arbitrary" myself, the more I read, and the more I burn. My Osburn flue probe shows from 400 to 950 as a 'safe' range. Isn't this kind of misleading especially for a newbie (I mean, an extended burn @ 900 deg in the chimney can't be a good thing, based on my own experience letting a start up fire get away on me once). The gauge is great, but I'm always developing a kind of a "feel" for when the stove is cruising nicely (and it's nowhere near 900 deg - usually much more towards 400 - 500 ). Seems I'm learning to not pay too much attention to the "ranges" on the dial, and just focus on the actual temp.
  24. begreen

    begreen Mooderator Staff Member

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    Yes, the burn is more efficient when the primary air is closed down enough to make the burn lazier and for almost all combustion to occur within the stove. That will pull in more air through the secondaries resulting in a cleaner hotter burn. Sending hot unburnt gases up the flue is both inefficient and dirty. If the flue gases condense on the walls of the flue while in this state, creosote will build up.
  25. begreen

    begreen Mooderator Staff Member

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    Good plan. The ranges are somewhat generalized. It's ok to get the flue hot for a brief period of time. I often will take the flue up to 800F (probe temp) with the first burn in the morning. But usually it doesn't get much over 600F.

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