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More or less water in an OWB???

Post in 'The Boiler Room - Wood Boilers and Furnaces' started by shawntitan, Jan 13, 2008.

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  1. shawntitan

    shawntitan Member

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    What's happening guys? For several reasons I've decided to go with a "traditional" OWB and I'm in the process of selecting one now. I have noticed that some manufacturers stoves hold 150+ gallons, while others, such as the Aqua-Therm, hold as little as 50 gallons. I've read what seem like valid arguements to go in either direction, but I'd like to hear from someone in the know which would be better, more water or less? Thanks in advance everyone, let me know what you think, and why.

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  2. Eric Johnson

    Eric Johnson Mod Emeritus

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    I assume they're using large water volumes around the firebox as a buffer to even out the firing cycles, but having that much water above ground and outside seems like a huge potential heat loss problem. Having your buffer or storage tank in the living space, such as the basement, makes more sense to me. I had a correspondence with a Taylor dealer on Ebay, and he claimed that having a large water volume was the key to efficiency, but everything else he said was absolute nonsense (85% efficiency, etc.), as was that claim. I'd take a good hard look at some of the new OWB gasifiers, Shawn. They probably burn a lot less wood and do it much cleaner than a conventional OWB.

    But to answer your question another way, a large volume of water will take longer to heat up, but once it does, it should last longer as well. If you are able to keep the fire going all winter, then a large volume of water might be to your advantage. If you think you're going to be starting fires from scratch, go with a smaller water volume. And if you want greater efficiency, such as it is with OWBs, then the smaller water volume (and a slightly undersized boiler) is probably also the way to go.

    Welcome to the Boiler Room, by the way. Let us know what you decide to do.
  3. Hbbyloggr

    Hbbyloggr New Member

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    Hi Shawn,

    Our OWB holds 300 gal. I reset the Hi/lo to a 20 degree differential. It's my feeling that the longer burn time gets the firebox temps hotter which deals with the smoke and gases with a little more efficiency . As far as heat loss , as an outside hot water storage container, it takes several days for snow to melt off the roof even when the internal temp is 180*. They are pretty well insulated to perform like that.

    That said, I would still look closely at the new generation of OWB coming on the market. One of the Forum members did an excellent review of Econoburn in action. I would love to see that same kind of review on all of the new gasifier OWB. Good luck . You deserve a pat on the back because no matter which way you go at least your are burning wood and not fossil fuel.

    Hbbyloggr
  4. Bob Rohr

    Bob Rohr Minister of Fire

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    The AquaTherm is a closed pressurized vessel. Royall also build pressurized model, with ASME and UL as I recall. One of the few that insurance companies like :) I feel pressurized style are easier to connect into current hydronic systems.

    Perhaps the non-pressurized units are well insulated to prevent jacket loss. BUT what about that 2" diameter hole in the top, steaming away?

    40-45% is probably a more realistic efficiency number, for non gasification types. And that's burning dry hard wood.

    I believe they are fired with 4'' square blocks of red oak when test fired for comparison. I'd guess most are burning in the 20- 30% efficiency in real life applications.

    The main thing is never over size OWF or they end up smoldering most of the time on the off fire cycle.

    The non pressurized types are much more forgiving when newbies over fire them. They basically steam away until the low water switch trips. On pressurized typed, they pop the relief(s) valves.

    It is almost impossible to burn a wood fire exactly to the load at all times, hense the need to add storage, or buffer capacity.
    How much is required is the million dollar question.

    hr
  5. Eric Johnson

    Eric Johnson Mod Emeritus

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    That you, hot rod?
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