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Heat Storage and Exchangers

Post in 'The Boiler Room - Wood Boilers and Furnaces' started by SteveJ, Nov 19, 2007.

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  1. Nofossil

    Nofossil Moderator Emeritus

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    I'm totally skeptical about that claim. Granted that there is some loss during startup and cooldown, there's no way that storage makes that much difference. If anything, our wood consumption increased slightly. I attribute that to keeping the house and hot water warmer with the storage, but there's no way that there's a 45% difference.

    Hard numbers:

    3.2 cords November 21 through March 15 without storage.
    4.5 cords November 1 through April 15 with storage.

    I haven't counted up degree days and compensated for hot water load, but perhaps there's a small efficiency boost with teh storage. I do know that comfort and convenience improved dramatically.

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  2. Donl

    Donl Feeling the Heat

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    Interesting observation Nofossil. Do you think maybe the resulting higher efficiency gained through a steady hot burn is negated by heat storage loss through the storage tank?

    Don
  3. Nofossil

    Nofossil Moderator Emeritus

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    No - there is some loss from the storage tank, but it's less than 10,000 BTU per day as close as I can figure it. For an indoor installation, I can think of only a few sources of boiler-related efficiency losses that would be affected by the presence of heat storage:

    1) Incomplete combustion during startup - less than ten minutes for me.
    2) Incomplete combustion and / or excess chimney losses during idling.
    3) Heat loss up the chimney from excess air blown through the gasification chamber as the fire dies.

    Heat storage allows you to have fewer fires, so startup and shutdown losses would be reduced. If you have half as many fires, you'd reduce those losses by 50%. However, I don't think that either one is a very big loss.

    Idling losses may be a bigger deal, but the EKO seems to idle pretty well - very little smoke, cool stack temps, and gasification resumes instantly coming back off of idle. Heat losses out the sides of the boiler just heat the house anyway.

    I just can't see where losses would come from that would lead to a big increase in efficiency from using storage. I'd but 10% or maybe even 20% if you twisted my arm a lot, but my own data shows a very small difference if any.

    I'm still a big storage fan - infinite hot water and and a warmer house are wonderful. I just don't see any justification in my experience for the efficiency claims being made.
  4. Eric Johnson

    Eric Johnson Mod Emeritus

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    I think there are a few more factors that you aren't taking into consideration, nofossil, mainly tied to your setup, which sounds pretty efficient to me to begin with.

    I think the bigger the boiler, the bigger the efficiency gain with storage. There are a couple of reasons for this. First, those of us with big boilers and no storage tend not to fill our fireboxes. Instead, we make a series of smaller fires, since we don't want the boiler to idle too much, and our output exceeds our load most of the time. That's less efficient for a number of reasons, including: 1.) Incomplete fuel 'preparation,' since the boiler is designed to burn full loads and we're only filling it, say, one-third full; 2.) Losses every time we go out there and stoke the boiler up. I open my boiler room door and let cold air in, I open the main loading door and let cold air in and sometimes, smoke out. I open the gasification chamber door just to watch it work. Sometimes I open the bypass damper and get the new load of wood burning good before initiating gasification. This all robs efficiency. 3.) And at least at first, we tend to run around the house turning up thermostats to keep the boiler from going into idle mode. This behavior tends to diminish when we realize that idling isn't such a big deal after all, but by then, everyone is used to having the house at 80 degrees, and they groan when it 'cools off' to the mid '70s.

    Add it all up, and it's a pretty big number. Add that to your observations, and it's even bigger.

    Contrast all this (which is actually a pleasure, since it gives me an opportunity to play around with the boiler) with setting the zones at 72 or 75 and forgetting about it, and firing the boiler once a day, and in my case at least, I don't think that 45 percent would be a big surprise. A welcome one, to be sure. Although it's not like I'm worried about running out of wood.

    I've tended conventional wood-fired boilers for around 12 years. Even without storage (it's almost a reality, I promise) this boiler is a lot easier to operate and get results from in a hurry. And even in its compromised state, it burns less wood overall, and a lot less wood for the heat produced.
  5. SteveJ

    SteveJ Member

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    Eric,

    You described my situation perfectly - lots of small fires and messing around with thermostats. I am racing you for storage but have all but conceded!

    Another issue with idling has been reported in this thread where idling equated to creosote which almost put an end to all heat demand for wouldchuckwood. Thank God he was home and caught the early stage of meltdown.

    So, I think that storage seems to be great regardless of the efficiency claims (I am slowly coming around to not beleiving everything I read :bug: )
  6. Eric Johnson

    Eric Johnson Mod Emeritus

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    I don't have any creosote buildup to speak of, surprisingly enough. I checked the chimney a couple of weeks ago and found only a thin layer of soot.
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