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Spin off from the Heritage or Mansfield thread...Min BTUs of a Stove

Post in 'The Hearth Room - Wood Stoves and Fireplaces' started by wg_bent, Aug 7, 2006.

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  1. wg_bent

    wg_bent Minister of Fire

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    All the time I've been reading this forum, it never made any sense that just burning less wood is the way to less heat. Every stove does have a certain minimum load to operate effectively, and I'd guess the larger the stove the more wood, Plus the more massive the stove, the more wood. BUT...I'm sure it's not that easy. If a large stove, let's say a Mansfield or Woodstock Paladian or PE Summit, Then the difference in mass of a stove would seem to be a factor. Does a more massive stove have more or less ability to put out lower amounts of heat (operate with fewer splits) than a equal size firebox with less mass?

    Many have said that runnig a stove full out most of the time is most efficient, but I doubt that we all do that.

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  2. Shane

    Shane Minister of Fire

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    Well since there is less mass to heat up on the smaller stove before it starts radiating it makes perfect sense that the smaller would be more efficient. There are less btu's being wasted in the warm up process and once warm there are less btu's required to keep the stove up to temp.
  3. BrotherBart

    BrotherBart Hearth.com LLC Mid-Atlantic Division Staff Member

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    And even more interesting for the scientific types to think about is if less efficiency is lost up the chimney by the smaller stoves. If they start throwing off heat faster and get to an efficient burn rate faster. In other words, do we sacrifice efficiency and wood by not getting up at three in the morning to feed the smaller stove?

    As Elk would say, HotFlame, got your ears on?
  4. MountainStoveGuy

    MountainStoveGuy New Member

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    But there is only X amount of BTU's in wood, and no matter how they are burned in X amount will get realesed directly porportioal to the amount of energy the wood contains. The trick is to get the additional btu's the smoke contains to release, hince secondary combustion. I do belive the carbon in the smoke is accounted for with the btu content of the wood. So if your not fireing off secondary combustion then you are loosing some of the btu that are stored in wood. When converting matter from one form to another, there os never 100% efficiency of the energy transfer, but that has nothing to do with the stove. The larger stoves put out more heat because you have more energy to release, due to more fuel in the firebox, and the process of secondary combution as a result of a hot firebox. At least thats how i see it. Im no chemist.
  5. BrotherBart

    BrotherBart Hearth.com LLC Mid-Atlantic Division Staff Member

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    So the mass of the little stove stops bleeding off energy sooner and the little stove lights off secondary combustion faster, therefore over the burn cycle it would be more efficient?
  6. MountainStoveGuy

    MountainStoveGuy New Member

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    Hmmmm... maybe. It takes more energy to get a large stove up to temp then it does a small stove, but if you have more wood in there on fire then i think it might be close to the same heat up time. Good question BB, but i think the difference is prettly negilable.
  7. BrotherBart

    BrotherBart Hearth.com LLC Mid-Atlantic Division Staff Member

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    Mostly I was thinking about the energy lost up the flue during heat-up to maximum efficiency. ie: Startup ain't the most efficient burn in the world for any stove.

    After the big boy is up to speed the difference would be incalculable. But the baby boy gets up there faster.

    Too much thinking. My brain hurts now.
  8. Roospike

    Roospike New Member

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    My vote goes for ..................a ................um ..............Hell , I dont know . Buy a Pacific Energy Summit with EBT Technology and dont worry about it . Ha . Sense i have the EBT i guess I wouldn't know . The stove does it automatically once the coal bed it set . I get secondary burn flames with 1 log or 9 logs . I guess I'll just have to keep an eye on the thread . Now i do think the Soapstone stove is in its own class vs the cast iron & steel plate stoves on this topic and the Soapstone stove would more-so need to hit a set temp .
  9. Roospike

    Roospike New Member

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    Now me being a fabricator / welder I can tell you that the more area of the steel the more heat is needed as per heating steel goes . If you have a set temp of heat on two pieces of steel and the larger the area of steel is going to dissipate the heat faster ie: less heat in the fire box . Also some stoves like per the Pacific Energy Summit the top plate is 3/8 thick . Going to take more heat to get the thicker of steel to the set temp vs a different brand say that has a 1/4 steel plate top . OR for the computer guru's .........The bigger the heat sink on a computer possessor ( ie: more metal / bigger area ) the faster the heat is going to dissipate and to end in over all, lost heat / less heat . The heat is going to go somewhere but is not going to be collected / stored as much , as fast in the lesser of the metal area .
  10. wg_bent

    wg_bent Minister of Fire

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    Roo, you got the point I was trying to make. Let's say you have a 30 lb load of wood. A fire in a small stove...Say a Jotul f3cb with a given volume of air will provide a certain amount of BTU output. Now, with the same 30 lb in the PE Summit with the same air volume will not do the same job. That big PE needs to have a certain minimum fire in order to operate efficiently. This really just says that you need to buy the right stove for the job, but people reading this should realize that you can't just go out and buy a PE Summit or Osburn 2400 and run real small fires. Some companies do specify a range of heat output, but I"m not sure that's the same as a minimum like we're stating here.

    So to wrap tie to the Heritage or Mansfield thread....your stove needs to be running at a certain output, so buy the stove that allows the closes match to min heating requirements, plus max output. I'd bet that will take a lot more reasearch.. :)
  11. Todd

    Todd Minister of Fire

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    Maybe thats true right at start up. But if you have already established a good coal bed and the stove is hot I don't think there would be much difference. Both stoves would put out about the same heat with the same amount of wood.

    Another twist is every time you open that stove door to reload the fire cools down and you pollute more until the temp comes back up to secondary light off. The more smoke the less the efficiency.
  12. Todd

    Todd Minister of Fire

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    Or burn a cat stove. Once the cat is lit off, you don't have to worry about secondary flames. In fact it can just smoulder away and still produce heat.
  13. Sandor

    Sandor Minister of Fire

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    No!

    Having burnt a medium and large Regency 2100/3100, I can say that you need a pretty good fire going to support secondary burn. With the smaller stove, it took a smaller fire to keep it going. With the larger stove, it took a much larger fire to keep the secondary going. And by the way, when it was burnt like that, it made way too much heat. Burnt it slower, and it smoked like a freigt train.

    I WOULD ALWAYS recommend the smaller stoves for all but the most brutal climates, or large open homes.

    Or like you said Todd, go with the cat! I am certainly a believer now.
  14. Roospike

    Roospike New Member

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    BUT , With the cat stove you still have to have a set abount of BTU;s to light off the cat . Point being made is how much more BTU's for the larger firebox ?/////////////////
  15. wg_bent

    wg_bent Minister of Fire

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    Roo, Sandor...Exactly!!! A CAT stove may do somewhat better in this regard.

    So now that we have a basic premise here. There's not much we can do here for the industry, but as Sandor said, a smaller stove might be the better choice between Herigtage or Mansfield. It will actually do a better job.
  16. Roospike

    Roospike New Member

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    ****BUT **** I agree with the lager stove needs more "heat / BTU's" to run vs the smaller stove box . ***BUT*** I dont think its going to make that big of difference to the point that you cant run the bigger stove in the smaller sq size house . I think your CAN run the bigger stove . The difference between the bigger stove and the smaller stove to run at its minimum heat range to run correct is so low in the BTU scale that its not going to make the difference . Lets take the large Pacific Energy Summit with 97,000 BTU as max rated vs a mid size stove max rated at 45,000 BTU's . ( not that we would run at max BTU's ) To run the stove at minimum to get secondary burn we are talking what ....... 12,000 -18,000 BTu's for example ? The small amount of BTU"s to get secondary burn is on the low side and the low side to get the larger stove to get secondary burn is low enough that its not going to run you out of the smaller size home / room to be debated . Pictured below is my Pacific Energy Summit stove heating our home when its around 55° out side . Not much heat is needed when its not that cold out side , correct . In the picture your will see 2 things . #1 low heat from two small logs in a larger stove rated at max 97k btu. #2 the second thing you will see is circled the secondary burn flames . Low heat + big fire box ( 3cf ) and still get secondary burn . You could run this large size wood stove in half the size house and be able to keep the heat where you wanted it . Again , I think the Soapstone stove is in its own class .

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  17. Roospike

    Roospike New Member

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    I agree one size of soapstone model stoves that you can over size them . If you have a BIG soapstone stove in a small room or small house . I think it could be controlled if we only are talking 30K BTUs .
  18. Sandor

    Sandor Minister of Fire

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    Roo, I cannot comment on PE stove; never burnt one. I can comment on Regency, since I owned two different sizes in the same model line.

    I would ask, what did the smoke output look like when you took that pic?

    Also, cat converters DO make a difference because they lower the ignition temperature of flue gasses down to 500 degrees, instead of the 1000 or so needed for secondary combustion on a non-cat stove.

    So, it is possible to get a slower, cleaner burn from the cat stove. This, in turn, gives you flexibility. Fire the hell out of it if its frigid out, and burn in low and CLEAN when you do not desire as much heat.

    That being said, cat stoves aren't for everyone because they need a bit more tweaking. But for me, sipping the Sam Adams (wintertime only) while messin with the stove is quite enjoyable. Just as soapstone is not for everyone. i.e.; people that demand heat RIGHT NOW.
  19. elkimmeg

    elkimmeg Guest

    The off market replacements cats, have another advantage. The ability to light off at 380 degrees not the oem 500 and continue ignition longer at 380. That 120 degrees makes cat stoves even more appealing. I can report that my after market combustor seems to be doing the job. I cleaned, not that it really needed, it at half season point and took it out this weekend. Neither time was it clogged They function better than the OEM originals, better yet 1/2 the price. How long the last I can not say It will take 5,6, 7 years to determine that. My 1987 stove functions cleaner and more effecient than my 3 year old non cat stove.

    Warren and Sandor there are two great informational topics going on now and this is one of them Good debates great information
  20. MountainStoveGuy

    MountainStoveGuy New Member

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    How could you know that your 1987 stove is burning cleaner then your new non cat stove? Thats crazy talk. You take that baby to a lab, i think you would find otherwise. Non cat stoves burn well within the relm of cleanliness of cat stoves. Most are under 2 grams per hour. Or mabey redifine "functions cleaner", maybe i misunderstood you. Why did the epa ax your stove from 1987? that would be a illeagle insall today.
  21. Roospike

    Roospike New Member

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    Hummmm ......." inquiring minds want to know "
  22. Roospike

    Roospike New Member

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    In the pic the coal bed is hot and wood seen is a reload , No outside smoke . The secondary burner is firing .
  23. elkimmeg

    elkimmeg Guest

    my stove passed the oregon Clean air specs the exact same specs adopted by the EPA in 1990. Same example happened in 1972, before un leaded gas was mandated in 1973. The manufactures de tuned their cars in anticipation of the upcomming Epa mandates No lab you are right just 30+ years burning experience, watching the exhaust plum leaving the chinmys comparing the amount of wood burnt watching the stove top thremo's. Unlike lab test a one event happening. I observed it for about 150 days. It might have helped a bit as I completely dissesembled and rebuit that older stove. Every refractory joint was scraped and wire wheeled clean before new refractory cement was applied Every gasket replaced including the cat plates on the back I sand blasted the interior to the poin of it looked like having never been fired. I pressurized it and checked for leakage. You are right I can' t prove anything. What I can tell you, is I got a productive 6 hour burn time out of a cat Intrepid II. Pretty damn good for that small of a fire box. You know it is possible to rebuild an engine to preform better than its oem state? Done that a few time as well too
  24. Rhone

    Rhone Minister of Fire

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    I think soapstone stoves with secondary burns have the highest minimum loads, followed by cast iron having less, followed by steel having the least. If soapstone secondary burn units are at one end of the scale I would imagine steel cat stoves on the other. I think on reloads that's cheating. My unit is soapstone, 550 lbs, and cold and fully loaded it will take 1.5-2 hours before its reached 180F and the fans turn on. It's like a barge. After the fire's out, it's another 2-4 hours before the fans shut off. From a cold start I need 4 log splits for my unit to do anything, otherwise I get smoke, rinky dink flames, secondary burn doesn't go off, and often times my unit doesn't get over 180F so the fans turn on. 3 log splits or less just can't get 550 lbs of soapstone and cast iron moving, all the smoke from 3 log splits is wasted and that seems to be rather significant because I don't get a lot of heat. 4 log splits, now I'm able to burn the smoke from 4 log splits instead of none, that increases draft, the higher firebox temps increases efficiency, it's just a pleasure to use. But on reload, lets say I load it up with 8 splits and then burn a fire. Once over, I go to reload, my unit is DAMN hot still. I could probably reload with 3 log splits and have it run fine, I don't think 2 enough. By the looks of Roo's setup and how lonely those logs look in that big unit I think he has a 3 split minimum from a cold start and he does seem to be getting away with 2 on reload. It looks like his secondary burn is lower than mine, that helps and it being steel surely helps also.
  25. Todd

    Todd Minister of Fire

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    You either have a draft problem, wet wood, or the soapstone firebricks inside your unit don't allow the firebox to produce secondary combustion like regular fire bricks would?

    When I had my old Energy King steel stove with the 3.2 cu ft firebox, I had no problems running small fires to take the chill off in my basement. Like Roo, the secondary combustion seemed to work fine no matter how much wood I stuck in there, as long as there was a good coal bed.

    Manufacture sq ft heating ranges very so much, and are way over stated. Don't go by them, I would figure 20-30% overstated or more. I still say a little bigger is better, and as long as you have good draft you will be fine with a larger stove building smaller fires, and you will have the extra firebox when you need it.
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