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Boiler questions. Tank size? Lifespan?

Post in 'The Boiler Room - Wood Boilers and Furnaces' started by captonion, Jan 13, 2010.

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  1. captonion

    captonion New Member

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    I am rating efficiency on amount of wood the unit will consume to do the job required. If it will take less wood using storage that IMO is more efficient.


    I am planning on driving to CT to pick up an Atmos Gs in march.I am just doing my homework before I commit. My brother inlaw is building me a tank out of aluminum, and all its going to cost me is the price of the material. I was thinking 400-500g would be OK?
    My plan is to run it through fored air via exchanger. I am also thinking two radiators in my grand room.

    I was hoping I could do this on 8 cords or less of wood per year. I know I can do 8-10 with forced air furnace. Just looking for insight!

    That I can..I would just be very dissapionted if after everything is hooked up I find out I am burning 15+ cords of wood per year, when I know I could have done it for under 10 going another route. Even though my wood is free I am still basing this on $70 per cord for heat. Five more cord = an extra $350 per year.

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  2. hkobus

    hkobus Member

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    Just make sure it will handle excess pressure, makes a large hole in any basement wall when it decides to blow. Also look at the disimilar metals issue (you will have steel, aluminum and likely copper)
  3. captonion

    captonion New Member

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    More questions lol.

    What kind of pressures will it run at? I am sure there are pressure relief valves to take care of anny issues?

    I am pretty sure the exchangers are aluminum so that should be fine? I don't know!
  4. hkobus

    hkobus Member

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    Pressure relieve valves are generally at 30 lbs, I am no engineer but it takes a lot of "meat" to handle that. Above that you need a safety margin when it fails, that is where you will be much better of with steel. Example: a farm fuel tank is vented and can handle unpressurised load. When the vent is blocked, she will deform rapidly with a bit of sunshine. Most here will use new or used propane tanks to do this job, they are build to handle more than the needed pressure and give some safety.

    The fins on the HX may be Al but the tubes are usually copper.
  5. karri0n

    karri0n New Member

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    $70???

    Are you talking about Cords, or fake cords?

    A cord is 4' x 4' x 8', 128 cubic feet.

    4 x 8 x 16" is a face cord. I know there are many people who refer to a face cord as "cord".



    It's really not a good idea to use a home-built tank, unless your brother is experienced in fabricating pressure vessels. Get yourself some used propane tanks.


    Once again, storage is not going to lower your wood consumption. If your boiler is properly sized,(which I would consider too small, as not using storage would be out of the question for me) and outdoor temperature is constant, you wouldn't need storage, but you would need to reload around 4 times a day or more. Storage ONLY allows you to go longer between feedings, and that's only if you put more wood into a larger boiler.
  6. ISeeDeadBTUs

    ISeeDeadBTUs Guest

    Don't be afraid to ask questions. We've all been there. My first year I thought storage would keep my oil boiler from coming on. But of course, I was wrong.

    You said the last house burned down. And you are going to put another +1,500 °F fire in the basement?!? :ahhh:

    Have you ever thought of cutting your losses on the Warm Air heat and just going radiant?

    Welcome aboard and again, don't be afraid to ask questions. What you SHOULD be afraid of is quoting 'cord' in a sentance that indicates it's not a cord. The 'cord' you refer to is a 'Gurly Cord'!
  7. captonion

    captonion New Member

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    Yup face cords. Can't imagine burning 10 bush cords.

    I must be a slow learner!

    Longer time between feedings means less wood used. No?

    My thought are that if well insulated storage is used there will be less heat loss as the water cycles if there is 500 gallons as opposed to 50. I may be wrong, thats why I ask.
  8. captonion

    captonion New Member

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    lol..... I know i know!
    My fire was electical, and my only other options are oil/propane. Out of those I like wood. Though I am also reseaching Geo Thermal.

    I can't go radiant as the house os already built. If i would have started from scratch that is the route I would have gone.
  9. ISeeDeadBTUs

    ISeeDeadBTUs Guest

    Yes and no

    Yes, yer a slow learner :)

    and No, storage is not going to appreciably save wood. Though you will fire on a schedule more to your liking, when you DO fire you will make up for lost time. You will need to reheat storage while heating the residence. This will mean a full bore fire and a probable reload. If you were not using storage, you would actually burn LESS wood during that particular firing since you would only be heating the residence.

    AND . . . if your boiler is not oversized, you may not be able to heat both at the same time. In that case, you won't even be able to schedule your fires.

    Many peeps on this site burn without storage. I think most that have storage like it, but will also tell you that it doesn't save THAT much in efficiency. I do not have storage and I burn about 8 cord mid-oct - mid April. If storage was going to cut my wood consumption to 4 cord, I would do it in a heartbeat. But it won't.

    BTW, sorry, I have no idea how to convert that to bush cords, Gurly cords, truckloads or loader cords.
  10. captonion

    captonion New Member

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    Bush cord

    A cord is 4’ x 4’ x 8’, 128 cubic feet.
    Face cord
    4 x 8 x 16” is a face cord

    Three face cord = One bush cord.

    So do you burn 8 bush cord, or gurly cord per year? If its bush cords,thats insane...24 face cord a year @ $70per is $1680 to heat a house for one season. You would be better off with Geo Thermal.

    Gurly cord?????????????????
  11. karri0n

    karri0n New Member

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    You need to make a bigger fire(and thus probably have a bigger boiler), and therefore use more wood to get the same amount of BTUs out, then save them for later.

    Let's break it down. I'll make up some numbers here.

    -------------

    Scenario 1, no storage:

    Your heat loss is 50,000 btu/hr

    You have a 55,000 btu/hr boiler

    You will need to keep the boiler cranking nearly 100% of the time, but you will put 4 splits in on each reload, every 4-5 hours(assume this as being a "full" boiler load). You need to keep the boiler loaded, and every 4 hours turns out to be loading 6 times a day.

    ------------------------------

    Scenario 1, with storage:


    your heat loss is 50,000 btu/hr

    you have a 55, 000 btu/ hr boiler

    You still need to keep the boiler cranking most of the time. Every once in a while on warmer days, some heat goes into the storage, but the house is constantly calling for heat, and the storage never really gets to temp.

    -------------------------------------
    Scenario 2, no storage:

    your heat loss is 50,000 btu/hr

    you have a 100,000 btu/ hr boiler

    You put 8 splits in the boiler, it runs for about 3 hours, then idles, and kicks on again after 2 hours. during this idle time, the boiler is still consuming wood,(albeit slowly, it's still going) and is also making smoke and possible creosote buildup. The boiler runs out of wood after 5-6 hours, and abruptly stops heating the house. The wood sorta lasts longer, but you're consuming wood and not gaining any energy out of it during the times that its idling, and, just like the above "no storage" option, as soon as the wood runs out, it stops heating abruptly. THIS is the only scenario where adding storage will save wood consumption.

    ---------------------------------------

    Scenario 2, with storage:

    your heat loss is 50,000 btu/hr

    you have a 100,000 btu/ hr boiler

    You put 8 splits in the boiler, it runs for about 2 hours, then the house stops calling for heat. The boiler still has a pretty decent fuel charge, and starts putting the energy into storage instead of idling. Once the house calls for heat again, the boiler stops charging the tank and starts putting heat into the house. You can now let the boiler burn all its fuel, and continue to heat the house from storage. Depending on the amount of storage, or how you want to run your schedule, you can run the boiler for 4 hours, then go another 8 hours just running heat from storage. This allows you to put 8 splits every 12 hours, instead of 4 splits every 4 hours. It's the same amount of wood, but a much easier schedule to maintain.


    It's not quite that simple, because while the tank is charging the house will still call for 50,000 btus every hour, but this is a decently accurate model. I hope you can now see why the storage doesn't reduce wood consumption, unless the boiler is oversized and idling.
  12. captonion

    captonion New Member

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    Another question?
    When the boiler is on idle does this not continue to heat the water supply that goes into storage tank?If there was continuous low flow circulation is should!
  13. ISeeDeadBTUs

    ISeeDeadBTUs Guest

    Actually . . .I hate to break it to you . . . a Face Cord is 4' X 8'. The length can be any, but must be specified. BTW, who actually burns 16" anyway?

    Um . . . I could not heat my house for double that if I burned oil. And I have a very efficient system with outside reset control. And I don't buy wood right now, but I hope when I do it will be tri-ax loads which are about $600 for about 8 cord. a far cry from $1680.

    But anyway, back to your questions . . .
  14. hkobus

    hkobus Member

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    Δ
    There are some variables again in this answer:
    yes, maybe if the ΔT gets too small for it to run full out, but it won't be much and it will loose some efficiency.
    Idealy you would build the fire so that it is almost done by the time the storage has reached it's highest temp.
    I think you need to visit Nofossil's site, it will answer a lot of you questions including real time burn records for you to watch. Look in the members list for his site or any of his posts.
  15. captonion

    captonion New Member

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    A boiler is starting to seem less, and less worth while, and not that efficient. I might as well just go Geo Thermal!
  16. sdrobertson

    sdrobertson Minister of Fire

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    Your at the point where the tough decisions are made. Everyone has to figure out how much your time is worth, and how you want to spend your time. If I went with fossil fuel (i.e. oil, natural gas, propane or electric) I could work more Over-Time and try to pay for my heat or I can spend hours outside, gathering wood with my family and heating with wood. Its one of the many choices you have to make in life. When I was a kid we heated with wood and I swore that I would never do that when I was a adult. Now that I have children and I have to work full time, I see burning wood as a advantage in that I heat my house for little money, I get to spend quality time with the family, and I can irritate my children all at the same time.
  17. ISeeDeadBTUs

    ISeeDeadBTUs Guest

    LOL, I similarly hated the whole wood routine. On at least one occasion I was labeled as 'lazy'. Funny, now that the ole man lives with us, he can't believe how much work I do with wood. And he thinks heat comes from a thermostat.
  18. Hunderliggur

    Hunderliggur Minister of Fire

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    Clean, "simple", efficient - Geothermal heat pump. OK as long as you have AC power for the utility or a big generator with lots of fuel.

    Wood - Always there, runs on low power (for boilers with pumps), powered by utility of solar panels if the utility is not working. I have LOTS of trees available.

    I have a wood boiler with propane backup (when the better half wants heat and I am not there to do the work)
  19. Reggie Dunlap

    Reggie Dunlap Feeling the Heat

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    Why would you buy a boiler that will only last 10 years?
  20. heaterman

    heaterman Minister of Fire

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    I'm curious as to how much over 190-200 you run. At least I'm assuming that is what you mean by much hotter. Are you taking the water past boiling and using pressure to prevent vaporization from occurring?
  21. Singed Eyebrows

    Singed Eyebrows New Member

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    After the creosote problem with my Energy Mate boiler I swore I would never burn wood again. The Atmos is not coating the chimney though. Times change & I was tired of being cold & paying $250 a month for the privelege of half freezing to death, Randy
  22. Gooserider

    Gooserider Mod Emeritus

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    One of the things NOT mentioned in all the discussion about storage or not, and it's impact on efficiency is the actual heat loads and how they change....

    Remember, everything we talk about in terms of heat loads is for "Design Day" conditions - IOW, the COLDEST it will ever get at your location... Most of the time it will be WARMER, and at that point your heat load will be less, as you have less temperature difference to make up for...

    If your boiler is less than adequate for "Design Day" you will not be able to heat the house to your desired "design temperature" on Design Day, but might be perfectly fine or even oversized the rest of the time... This can actually be a viable approach if you have a backup system like a fossil burner or a wood stove that can kick in to make up the difference, or even if you don't mind piling on some extra clothes...

    If you boiler is exactly sized for Design Day, then it will be OVERSIZED for the rest of the year. If it is oversized for design day, then it will be even more oversized the rest of the time...

    As has been covered and quite thoroughly beaten to death, storage does not offer any advantage on design day with a properly sized boiler - the boiler will need to run flat out all the time, and the storage will never charge. If the boiler is oversized, you will save some efficiency by reduced idling on design day, but mostly your advantage will be in "time shifting" your burns to better fit your schedule.

    Where you WILL see some level of savings is in "shoulder season" - outside of design day conditions, but where you will still want SOME heat.... Without storage, your boiler will be way oversize for the conditions, and will spend most of it's time idling, and slowly burning wood w/o doing any useful heating. With storage, you burn flat out, heating the storage, and then let the fire go out. No idling! You then pull from the storage until it drops below usable temps, and then you need to build another fire and repeat - could be 3-4 days between fires.... For the extreme example of this, I would point at the person that wants summertime DHW production - w/o storage they still need to keep a fire going, 24/7 even if it's idling 99% of the time, or keep building tiny fires and waiting for the boiler to warm up each time they have a demand... W/ storage several of our users report building one fire a week or less...

    Note that to get maximum benefit out of storage, you need to maximize your operating temperature "swing" - if you are going to use a W/A HX, then I will agree with the others that it should be way oversized - though note again that in warmer than design day temps, even a nominally sized HX will provide adequate heat at lower water temps, since "adequate" is a lower number of BTU/hr...

    In terms of pressure vessels - unless your brother is an expert on designing and building them, I would STRONGLY advise against any kind of home brew, pressurized tank. I would also advise against doing aluminum in any system that also contains copper and steel - the aluminum will suffer greatly from dissimilar metal corrosion, and likely fail in a hurry.... In terms of pressures involved - typical operating is 12-15psi, most pressure relief valves are rated to blow at 30psi (and are likely to start dribbling at anything over 20) boilers are typically tested at 60psi or higher. The commonly used propane tanks were rated in excess of 600psi when they were in propane service...

    As to wood vs. Geothermal - Geothermal has a high initial install cost for ground based, and tends to be undersized for the job because the sales guys don't want to make the system price to scary... While it is relatively efficient as electric heating systems go, it still has a fairly high monthly operating cost, such that at least some calculations say that the payback on a geothermal system exceeds it's reasonable life expectancy. OTOH while a wood gas + storage setup also has a high initial install cost, (Less than geothermal, but probably not a LOT less...) it has much lower operating costs, especially if you cut your own wood... (We just had a discussion about this a few days ago in a different thread)

    Gooserider
  23. Singed Eyebrows

    Singed Eyebrows New Member

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    I would also strongly advise against building a pressure vessel especially one that is not round. Few co's have ever offered rectangular tanks, the ones that do have them stayed from one end to the other. What I personally would not hesitate to do is to cut down a propane tank so it could stand upright. Do not cut off the head though, they distort & are not going to line up decent. Leave at least 5" of tank on the head. Bevel both sides & have a competent welder weld it up & you will have a safe tank, 30 psi will be no problem. DO NOT weld up with a low power mig welder. I could not find propane tanks for under $500.00 here so I had one made. Oil storage tanks even if round are unsuitable as a pressure vessel. Do the math on 15 to 20 PSI & it gets scarry fast, Randy
  24. captonion

    captonion New Member

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    After alot of research Im gettin Geothemal installed in March. It should pay for itself in 8yrs by my figures, then FREE HEAT.It will also save me cutting wood when I'm old! With air conditioning to boot.

    Thanx for all the help guys.
  25. Donl

    Donl Feeling the Heat

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    We had Geothermal forced air heating in our last house. We loved it! If I were to do it again I would go Geothermal radiant heating as backup for a wood boiler. I can't stand the thought of not being able to cut and burn wood. What would I do in my old age? Just one question, how do you figure on getting FREE HEAT after 8 years?
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