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"Losing heat up the flue"

Post in 'The Hearth Room - Wood Stoves and Fireplaces' started by nola mike, Dec 29, 2011.

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  1. nola mike

    nola mike Feeling the Heat

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    Keep seeing this posted again and again on this site, that leaving the air open somehow leads to lower stove temps and losing all of your heat up the chimney. I think this leads to people closing down the air too early and ending up with ultimately lower stove temps. While having the air open does heat up your chimney, and lead to lower efficiency, I don't think it leads to a cooler stove. In fact, if you look at all the overfire stories, they mostly involve forgetting to shut down the air, leaving a door open, leaking gaskets, etc. I've found that letting the stove burn open for a little longer before shutting down leads to ultimately higher cruising temps and better heat output. It also lets me close down further without choking the fire. Also, if max heat output is your goal (vs. longer burn time), shutting down all the way isn't always the way to go, at least on one of my stoves. While I can get a hot fire when closed down, or 1/8 open, I get a hotter fire 1/4 open. There's definitely a sweet spot. This is all probably obvious to most on here, but it took me a year to figure out as a new burner...
    Oh yeah, and more secondaries doesn't necessarily mean a hotter stove.

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  2. MTMike

    MTMike Member

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    Mike,

    We have the same stove and I too have found this to be true in the week that I've been burning it. I find that if I leave it open for 7-10 mins (instead of 3-5) the fire is hotter and more intense, and when I shut the air down incrementally and cruise at 1/4 (instead of close or 1/8) I seem have better heat output and more activity in the secondaries. I took the advice in my newbie post last week and then applied it and came to this conclusion in the last few days.

    Mike
  3. oldspark

    oldspark Guest

    Good topic,YRMV, some people cant get that through their thick heads and try and impose what works for them on the rest of the world, then you reply it doest work that way on your stove and the finger pointing starts. :cheese:
  4. oldspark

    oldspark Guest

    Can you provide a list of those stoves?
  5. LLigetfa

    LLigetfa Minister of Fire

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    My RSF uses a thermostatic control for combustion air. While it does provide a degree of automatic regulation, I still find that it has a sweet spot. Less is more.

    For years I ran the stove with too much air and wasted a lot of wood. It seems counter-intuitive to turn down the air to get more heat out of the stove. I now will not run the stove air set above the half way point. Most often it is at 1/4 or less. I even modified the zipper air to be able to cut it back.
  6. HotCoals

    HotCoals Minister of Fire

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    On secondary air?..interesting if they do.
  7. Oldhippie

    Oldhippie Minister of Fire

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    I'm thinking you mean thermatically controlled. Does that mean temperature controlled?

    I think I get it, if "it" is finding the sweet spot between getting the airflow high enough to raise the stove temp to maximize heat transfer to the home the stove is in over an acceptable burn period, while minimizing the lost heat sent out the chimney to heat the neighborhood.

    But it is a bit of an art, isn't it?
  8. gyrfalcon

    gyrfalcon Minister of Fire

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    Oh, brother, ain't it the truth. And there are sooo many darn variables. I have a harder time with this because my stove is so small and not really up to the task, but if I don't get the heat out of it I got the last burn cycle, maybe the splits are too large/too small, not quite the same amount, not exactly the same temperature when I reloaded, not the same depth of coal bed, etc., etc., etc., it's really hard to make sense of what it was that gave me, say, only 400 instead of 450. All vastly complicated by the time lag between what's going on in the firebox and when the temperature registers on the outside of the soapstone. Grrrr.
  9. begreen

    begreen Mooderator Staff Member

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    What Harman wood stoves have a thermostatic damper? FWIW, I think most of the stoves mentioned have a thermostatic damper on the Primary air.
  10. oldspark

    oldspark Guest

    Secondary air control is a new one on me, that's why I asked but its a no go huh? Not that familar with the brands he mentioned.
  11. LLigetfa

    LLigetfa Minister of Fire

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    I cannot speak for all stoves, nor for the stoves mentioned, but highly doubt any EPA stove would have unregulated air, either primary or secondary. Doghouse (zipper) air is the exception. If by regulated you mean only thermostatically, I still cannot speak for them.

    Stove manufacturers cannot even agree on what is primary and what is secondary. They also do not all provide separate controls for primary versus secondary air. Now the zipper air would be considered primary but the zipper does not provide 100% of the primary air. The airwash for the door glass is usually considered to be primary air. The superheated air to the "secondary" tubes would be considered secondary air.

    On my RSF, there is but one air control where the OAK connects. If thermostatically regulates all the air except for zipper air. Some of the air washes down the glass as primary and some of it comes out the secondary tubes.

    If the manufacturers cannot agree on the nomenclature, how are we to agree?
  12. oldspark

    oldspark Guest

    OK now you have me confused, the summit has a wide open hole to the baffle all the time so help me out here.
  13. woodmiser

    woodmiser New Member

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    I thought the holes that feed my Clydesdale's secondaries were unregulated? See the square hole down in the lower left? There is one on each side.

    Attached Files:

  14. oldspark

    oldspark Guest

    Woodmiser-I am sure they are not regulated and I think BB said it was not on his 30 so like I said I am confused on what he is saying.
  15. Backwoods Savage

    Backwoods Savage Minister of Fire

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    Mike, perhaps your post or this thread is aimed at me because many times I have told people that leaving the air full open wastes heat going up the chimney. I stand by that statement still. However, perhaps some misunderstand what I am getting at. I see folks who leave the draft open full for a half hour or more and this is where I mean they are wasting heat and fuel. Also please realize this can vary a lot by the fuel you burn! Yes, the fuel is still the main factor.

    On a cold stove, when you close down the air will be a lot different from when you are reloading the stove. For example, I can reload on a large coal bed and have the draft turned down within 5 minutes or 10 minutes tops. When I start with a cold stove that time lengthens a lot. For flue temperature, we try to get our flue to 400 or a maximum of 500 and this is measured on a horizontal single wall flue pipe.

    I can even go back to my days as a young lad which was a few years before the epa stoves. I learned very quickly to turn the flue damper down once the fire got a bit riled up. Otherwise things would get out of control and I do remember seeing our stove pipe red hot a few times when someone else was tending the stove. That scared the heck out of me even as a young lad. Does it even worse now. But the key to getting heat was not to get that fire roaring, but to tame it down and keep the heat in the stove rather than the chimney.

    Definitely every stove and installation can vary a bit but there are still some general guidelines that still work. Also, most folks want to talk about a time factor. That is, we leave the draft open x minutes then cut it down to half for x minutes, etc. For the most part, I still go by what the fire is doing and what the stove and stove pipe is doing for setting the draft. I can not say definite that I wait 5 minutes to turn the draft down because the may be right sometimes and may be wrong other times.

    For those who want to "clean" their chimneys with super hot fires, go right ahead. As for this house, we'll stick with burning good fuel and not getting things super hot.
  16. LLigetfa

    LLigetfa Minister of Fire

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  17. oldspark

    oldspark Guest

    You did read the last long thread about the EBT did you not, I have a WIDE OPEN hole to my baffle ALL THE TIME.
  18. Battleaxe

    Battleaxe New Member

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    The secondary air intakes are unregulated on my performer, but the hotter it gets the better the chimney draws and the more air the secondary tubes will suck in as the primary air intake is closed down. The doghouse air intake is also unregulated, so it also draws more air as the fire gets hotter. So the hotter the stove gets the more doghouse and secondary air it sucks in and the less primary air it needs. Ideally the stove gets hot enough that you have an active fire without any primary air. There are a lot of variables that need to be adjusted for with each fire: outside temp, wood type, wood moisture content, wood arrangement in the stove, points at which you decide to close the air down a bit, fans on the stove or not, etc... I look for nice lazy secondary flames to not burn through the wood too fast, but you need the fire to remain active so you can't close it down too much. Sometimes I close it down all the way, sometimes not. If its cold out and I want to warm up the house then I get the stovetop hotter (~6-700) even though I'll burn through a bit more wood. If its not so cold out I stay in the ~450-500 range to conserve wood and not get the house too hot.
  19. seeyal8r

    seeyal8r Feeling the Heat

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    On my insert Large Regency and all variables aside

    I need enough primary air to keep the coals hot which is about 40-50% open, for me usually. With enough heat in the box itself to cause enough draft to pull air through the secondaries. If my coals don't get air, I don't get much secondary for very long. If my coals get too much air through the primary then the draft being pulled through the primary doesn't result in enough draft through the secondaries for any visible burn unless its happening above the visible firebox (which I have no way of knowing).
  20. LLigetfa

    LLigetfa Minister of Fire

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    OK guys, cut me some slack.

    There's a difference between unregulated air and what a lot of people call the EPA port. Many EPA stoves limit how much you can turn down a stove. That doesn't necessarily mean the secondary air is 100% unregulated. Again, I am not familiar with the inner channels and workings of all models, so this is a generalization.

    My RSF has a notch cut out of the butterfly that prevents the regulator from cutting off the air 100%. It's like the idle screw on the carb of my chainsaw.

    Now we can't even agree on the term "regulated".
  21. oldspark

    oldspark Guest

    Your words not mine, unregulated air means, drum roll please-unregulated, self defining IMHO, it will pull air from the path of least resistance and saying you are regulating it by turning down the primary air is a stretch if that is what you are saying.
  22. Huntindog1

    Huntindog1 Minister of Fire

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    Good topic, I would say it depends on how good your chimney draws. I think mine draws too much as I can close my pipe damper fully and close my intake air fully when the stove is hot and the thing keeps cruising along.
  23. woodmiser

    woodmiser New Member

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    Same here with my Equinox.
  24. LLigetfa

    LLigetfa Minister of Fire

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    I had the same model RSF in my former home and it had a much taller flue and so I had too much draft for the size of the EPA notch and the size of the zipper air. When I loaded it up for the night, it would run-away to the point it melted the air wash diffuser and permanently etched the glass. I plugged the hole for the zipper air but then it would build up with too much coals and I'd have to work at burning down the coals. The dealer suggested replacing the butterfly with one that had a smaller notch but that would have meant pulling out the insert and I had it all tiled and a mantel surround already. I sold the house instead.

    My current RSF has a smaller notch and a shorter flue. I also added a control on the zipper air so that I can close it when I want or open it to burn down the coals. I can now close the primary/secondary air regulator all the way and not have a run-away issue regardless how dry the wood or how I load it. I also added a positive shutoff to the OAK although it only gets closed if the stove is cold.
  25. woodmiser

    woodmiser New Member

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    What is zipper air?
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