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Whats up with these Different BTU ratings ?

Post in 'The Hearth Room - Wood Stoves and Fireplaces' started by HDRock, Jan 18, 2013.

  1. HDRock

    HDRock Minister of Fire

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  2. Woody Stover

    Woody Stover Minister of Fire

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    I would take all the ratings with a grain of salt, EPA or mfgr. My little Dutchwest 2460, 27300 and the 30, 28337? Doesn't seem like there would be much difference... :confused: Or maybe these 30 guys are just pulling our legs, talking about how much heat they toss. ==c On the other hand, not really sure how the companies come up with their stove output ratings, either...
    BrowningBAR likes this.
  3. ddahlgren

    ddahlgren Feeling the Heat

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    It seems hard to believe that you could put some absolute rating on the BTU output with wood.
    things that come to mind is what kind of wood oak or pine
    kiln dried or 30% moisture or more.
    low and slow for a long burn or over fired
    Wood is justnot a fixed btu per unit volume fuel like oil gas or coal.
  4. jeff_t

    jeff_t Minister of Fire

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    Don't waste any of your brain thinking about BTU ratings. There is no standard for what a manufacturer can write, and EPA tests aren't exactly real world. Look at firebox size.
  5. jotulguy

    jotulguy Feeling the Heat

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    Here is an explanation.....i hope it uploads.

    Attached Files:

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  6. Huntindog1

    Huntindog1 Minister of Fire

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    BTU's ratings can be calculated in many ways. Plus if a stove can let more air in it will burn at a higher rate and BTU ratings are usually BTU per hour.

    If you look at the BTU rating for a certain type of wood per pound of that wood. Or you can look at BTU per cord and you know how many cubic foot of wood is in the cord of wood. You then can calculate down how many btu of wood you can get in say a 3 cubic foot fire box.

    Its an approximation for sure.

    When your shopping around and do want to compare something then make sure your using the EPA tested BTU rating. Ask the manufacturer for the EPA test results.
    As the EPA testing is a standardized test that has to be done by a Certified lab. It uses the same type wood and the same process for every stove. The number will be lower as the EPA uses a lower quality wood to make for a worse case scenario to make the stove can burn pretty clean. But they use the same lower quality wood for every stove and every test. Its not perfect but as consistent as they can reasonably get.
  7. HDRock

    HDRock Minister of Fire

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    Ya it works , Thanks that helps

    That is all a given, obvious

    When your looking for a used stove , to fit your needs you have to have something to go by, and if I can't find any other info on a stove, besides whats in the EPA stove list, then I need some idea why the numbers, are so different than what manufactures state.
    Some people selling used stoves don't list , or even know ! things like fire box size , unless they actually go measure the inside of the box, and just because the person selling a stove knows nothing about the stove , it doesn't mean it's not a good stove.

    Finding a used stove to fit your needs is very different than selecting a new one.
  8. Huntindog1

    Huntindog1 Minister of Fire

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    Dont forget its also depends on how well your house is insulated. Having good windows helps alot.

    There are guys buying big stoves to heat the world not as much their house.
  9. HDRock

    HDRock Minister of Fire

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    ;lol Thats funny cuz ,I can almost heat the world with the 8cbft fire box stove I have
    If I wanted it to be 100 in my house ,I could get it there, no prob
  10. Huntindog1

    Huntindog1 Minister of Fire

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    There is a hugh increase in heat when I use my good dried oak or hickory.

    So focus on good wood supply also.
    milleo likes this.
  11. Jags

    Jags Moderate Moderator Staff Member

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    Take the model that you are considering and use your googlefu to locate the manual for it. Firebox size is one of the only true ways to rate a stove. The other considerations are: tube burner, cat burner or a combo of both or smoke dragon.

    Basically, that is it. You should have already decided on a short list of specs to fit your need (ie. 3 cu. ft tube burner, or 2.7 cat burner, etc.) then find the stove that fits your needs.
  12. ddahlgren

    ddahlgren Feeling the Heat

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    The EPA doc is interesting and actually does nothing useful in testing. A better test would be to put the stove in a sealed room or one with a known heat loss and run the stove for an hour with a standard wood and measure the temperature change. The current EPA test does not account for thermal efficiency. How much wood a stove can burn in an hour has little to do with BTU rating output only BTU input. If I add a secondary heat exchanger to my stove it will put out more heat but the EPA test numbers will not change. So in my personal opinion useless. They would be a lot more useful if they at least took into account stove temp and stack temp as it would give a clue as to how much heat goes into the house rather than up the stack pipe.
    Trilifter7 likes this.
  13. kborndale

    kborndale Member

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    How would your insulation and windows change the btu output of your stove? I would certainly keep the heat in longer but the stove is going to be able to put the same btus regarless. If anything little insulation and bad windows would increase your btus because you would have a less restricted draft.
  14. Jags

    Jags Moderate Moderator Staff Member

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    Not sure I buy that theory. You would have to be comparing it to a completely air tight home. So tight that it would have negative pressure if ANY air went up the stack. If that was the case, you wouldn't even be able to get a fire going.
  15. clemsonfor

    clemsonfor Minister of Fire

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    Its similar to thier effeciency rating. Myseriously all CAT stoves according to them are 73% efficient and all tube or reburn type stoves are like 62%????

    But i think thier test wood is not dried to 20% like many of us try and use so we get more btu's our of a cuft then thier test and they also i think test with doug fir as well.
  16. ddahlgren

    ddahlgren Feeling the Heat

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    It seems like most stoves I looked at when thinking about a new one and got some sticker shock was they all have very similar design heat exchangers. I ended up buying a used one though finding out way too small. I am seriously thinking about either finding a used larger one in the summer or building a secondary heat exchanger so at least I can get more heat for the painfully too short burn. According to the manual for the one I have it is listed at 68%.
  17. WoodpileOCD

    WoodpileOCD Minister of Fire

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    Was doing a little research on an Osburn 2400 I saw on CL and found this on their site. Talk about a difference in results.

    Don't know how you would get 100k BTU out of a 3.2 cu ft box but this is what they claim.

    • Maximum output - EPA test wood44,100
    • Maximum output - seasoned cord wood100,000 BTU/h
  18. Jags

    Jags Moderate Moderator Staff Member

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    Huh...wonky numbers from a MFG. Who wudda thunk.
    35 ton splitter anyone??
    Just another example of marketing hype.
  19. rideau

    rideau Minister of Fire

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    Since LHV per pound of hardwood is around 6000 BTU/pound, I guess you'd have to burn 17 pounds of wood per hour minimum to get that much heat. If you could get 85 pounds of good dry 20% MC hardwood in the stove, your coals would be toast in 5 hours.
  20. rideau

    rideau Minister of Fire

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    Yes, they test with dimensional Douglas Fir, but I would think for sure it is dry. First of all, it is cut, then processed to a small dimension with a lot of surface area that will dry quickly, even if not kiln dried, which it may be.
  21. rideau

    rideau Minister of Fire

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    If how much wood a stove can burn in an hour has little to do with BTU rating output, then ther gall those arguments that only firebox size matters.

    I definietly agree that BTU input into the heated area is the crux, and should be measured and available inforation for purchasers. Wish we could ge the EPA to test for this. You'd think they'd realize that the smaller the stoves we could use, the less emissions, the less wood gathering, the less trees cut, the less gas and oil used in chain saws and autos, the less secondary emmissions caused by each stove fuel acquisition. We're a big group. Why doesn't someone start a lobby to the EPA to test for this? Maybe also to the consumer protection agency? Any takers?
  22. ddahlgren

    ddahlgren Feeling the Heat

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    Consumer reports??? They test everything else it seems. And the more plentiful wood becomes too BTW.
    Being an engineer and ex boiler mechanic 40 years ago it has gotten my interest. There is a very large difference between combustion efficiency and thermal system efficiency.. I see a K wire themocouple and note pad in my immediate future ..like tonight.
  23. Jags

    Jags Moderate Moderator Staff Member

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    Very interdasted.
    But how will you compare input to output? Gonna weigh the wood? Monitor stack temp? Inquiring minds want to know.
  24. Machria

    Machria Minister of Fire

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    There is a good strong discussion about this topic (EPA tests) in the Woodstock PH thread, starting about page 11 and goes to about 15 or so. Some flame throwing (no pun intended!) but, I think a good discussion with lots of different viewpoints. Mine of course is the only on that is correct though! :) http://www.hearth.com/talk/threads/woodstock-soapstone-progress-hybrid-stove.88516/page-11

    In summary, I personally have thought alot about this long and hard. While I have very little stove experience (just got my stove a month ago), I have a strong scientific background and am pretty good at analyzing and pulling apart testing results (it's a big part of my job/carreer). That said, I think the EPA numbers are somewhat meaningfull, and decent for comparison purposes (compare one stove to another), but are certainly NOT designed to do that exactly (the EPA is intersted in emmisions, not heat output). They are certainly flawed and do not depict real world outputs, however they do provide a setpoint comparison on a level playing field. If one stove performs better in EPA tests, it will likely perform better in the real world. Will the percentages of performace be exactly the same or ratios of them stay the same? No. But I think they will give you a reference point, you would not otherwise have. Using only the firebox size can be a big mistake. The reason being, think about the difference in heat output between a large 3.0 cf fireplace (non airtight, non epa...), and a modern EPA 3.0 cf fireplace. They both are the same size firebox, can be loaded and burn the same amount of wood, yet one sends virutally ALL of it's heat up the chimney, while the other sends most of it's heat into the room. One burns 4 splits for 8 to 10 hours, while the other burns 4 splits in 30 minutes. But they are the same size firebox, right? Why such HUGE differences in heat output then? Becasue of the difference in design of the unit. One traps the exhaust and heat, and sends it swirling around the box, and into baffles and a heat exchanger, the other goes straight up the top of the box and into the chimney.

    The exact same differences can, and do exist in the different designes of stoves. Some capture the heat and radiate and/or convect it into the room, and some let it go up the chimney. Some don't burn all the fuel from a load, and let alot of it go up the chimeny un-burnt, while others burn every little last bit and extract all the heat before letting it go up the chimney. So I think the EPA tests while not perfect at determining heat ouputs by any means, do give us a decent reference point to compare how they might perform under a set of conditions. The results will vary in your home with your setup, draft and environment, but the results will vary the same way for the most part with any stove you install whether it is better or worse results compared to the EPA tests.

    Lastly, as pointed out by some in the Woodstock thread, there very well may be some error in the results reported. Some of the units results seem to be way off based on real world comparisons. Those I can't answer for, were the test done incorrectly? Was there a typo by mfgr or EPA....? Or, maybe those units just are not as good as people think they are , who knows? But that leads me to the below:


    EXACTLY! I was dumb-founded when I started researching for my stove purchase, and found no real standard heat output tests. Also, little to know info on how the EPA tests are done, why, where and by whoom... There are no real tests done excpet by mfgrs themselves on heat outputs rather than emmisions testing. I can't believe there is no wood stove test lab somewhere (UL or other?), that takes a stove, puts it in a environmentally controlled 30* air temp, 20% humidity or such and loads it full of wood and let it burn while monitoring load weight, stack temps, and room temps at different distances (say 5', 10', 20' and 30') over time, then graph it all, and release that as the official stoves OUTPUT. Just about every other industry has something like this. Why not wood stoves? Maybee I should open a Stove test lab? Could be a fun job. ;)
  25. begreen

    begreen Mooderator Staff Member

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