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1000gal or 2000 gal???

Post in 'The Boiler Room - Wood Boilers and Furnaces' started by nwomatt, Feb 6, 2013.

  1. nwomatt

    nwomatt New Member

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    I have a vigas 60 sitting in my shop hooked to nothing. Plan to have it fired next fall. Just trying to decide on either two 500 gal tanks or two 1000 gal tanks. Have room for either size although the two 500 gal tanks would fit a bit better. My house a good size 4 level split with new doors and windows and well insulated. I also plan to heat dhw and shop (44x48) new and insulated well. I don't want it hot in the shop just above freezing.

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  2. BoilerMan

    BoilerMan Minister of Fire

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    What type of heat emitters? I'd be in the boat bigger is better, but your heat emitters will have the greatest impact on the useable heat that a given volume of storage can provide.

    TS
  3. nwomatt

    nwomatt New Member

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    Forced air in house radiant in shop
  4. logger6644

    logger6644 New Member

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    Hi neomatt, storage is your battery, a way of storing heat, and leveling out loading issues. It also allows the boiler to burn for extended times, avoiding the problems associated with short cycling the boiler, where it starts and stops based on demand of your heating system. There are several issues that affect your choice. You need to keep the water hot enough in the storage system to avoid feeding cold water back to the boiler. You need to build up the heat in the storage every time you let it cool down so there are startup considerations. The space it takes up and the need to insulate the tanks to avoid the heat losses are also concerns. Once you have storage to level the load issue for the boiler, any more is of questionable usefulness in my opinion. Start with 500 which would be plenty to deal with the boiler loading issue. After that you are trying to build up a buffer of heat storage to allow yourself longer downtime between having to load the boiler. You are not going to burn any less wood, you just have to burn like crazy to build up the storage and then you can coast for awhile, then burn like crazy again. It's easy to calculate how much heat is stored. Just multiply 8 pounds per gallon times how many gallons times the difference in the peak and low temperatures you expect to run in your system. For instance 8 x 1000gal x (180-140F) = 320,000 BTU's. 2000 gallons...twice that. Just remember no free lunch. You take it out at night for instance so you can sleep in, you have to put it back somehow before you go back to bed.
  5. Beerdog

    Beerdog New Member

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    Have you done a heat loss calculation? If cash and space are not concerns then the decision hinges on some calculations. How many total Btus will the Vigas 60 deliver in a burn cycle? How many Btus will your home/shop use (heat load calculation necessary)? What is the supply temperature to your heating distribution system and what is the maximum temperature you can deal with? Many systems typically cycle between 140 and 200 F so that's a 60 degree differential. A 1000 gallon system will store as follows:

    1000 gallons x 8.345 lb/gallon x 140 degrees = 1,168,300 Btu. If you assume that your home uses 100,000 Btu/hour then that heat will last a little over 10 hours before the storage tank is empty of heat. If your home consumes 200,000 Btu then you'd run out of stored heat after 5 hours. On warmer days, the use is less and stored heat will last longer.

    The rate you produce heat is also important. You may have a "200,000" boiler but is that a continuous rating? The average produced over a charge of wood until it's consumed? You can get an idea of how long a load will last if you know the volume of the firebox. You can get an approximation of how many Btus a burn will create if you know the volume of wood that will fit in the box. Don't forget that while you generate heat from the boiler, it goes to both the home and the excess gets banked to storage. So if your home uses 100,000Btu/hour and you have a 200,000 Btu /hour production rate then you bank 100,000 Btu for the time when the boiler is not supplying heat.

    My gut feeling is that a 1000 tank will serve you well but 2000 can hold twice the heat. This gives you capability to run longer between burns if the storage is charged. But bigger tanks may require you to fire the boiler for longer periods to take advantage of their increased storage. A sweet spot for me is to fire once a day, but twice a day would not be a problem... just a bit more inconvenient to do when there are so many things to do before running out to work in the morning.

    If it were me, and cash were not an issue, I'd opt for the additional storage. I see no downside to it if the space and cash are available, and it can make your life easier in the long run.

    John
  6. JP11

    JP11 Minister of Fire

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    I have 1000 with my Vigas 60. If space weren't an issue.. I'd prefer 2000. You should be able to get 800k BTUs out of a FULL load of hardwood. That won't fit in my 1k.

    I think 1500 is probably closer to matched size wise. I'm running mine from 195 down to 135. Sounds like you'll be heating the same amount as me. If you hot air for the shop needs hotter water.. I'd definitely want the 2k gallons.

    JP
  7. nrcrash

    nrcrash Member

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    Like a wise man once told me... "the bigger the better the tighter the sweater"
    flyingcow likes this.
  8. EffectaBoilerUser (USA)

    EffectaBoilerUser (USA) Member

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    Based on my past experiences I normally see 1,000 gallons used with a 35 or 40KW boiler and 2,000 gallons used with a 60kW boiler

    The reasoning behind this is:

    Using a 50F delta, the 1,000 gallons can accept approx. 50 x 8.3 x 50 = 416,500 BTU's

    At 35kW (122,000 BTU/hr) and a 4-5 hour burn cycle that works out to about 450,000-500,000 BTU's


    For the 2,000 gallon tank this would double to 833,000 BTU's

    At 60kW (205,000 BTU/hr) and a 4-5 hour burn cycle that works out to about 800,000-1,000,000 BTU's

    In the cold winter months the heat loads would obviously consume a good portion of the BTU's being produced.

    However, in the shoulder seasons and summer time the heat loads would consume less of this BTU output and thus more BTU's would go into the tanks.

    In summary, the 1,000 and 2,000 gallon storage tanks as stated above are only guidelines. These can obviously be adjusted to correspond with individual applications and structure heat losses.

    Brian
  9. jebatty

    jebatty Minister of Fire

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    Your boiler should have return water protection to make this a non-issue. I charge my 1000 gal tank to 190F typical and run it down to 90-100F, all used to heat a radiant floor. Return water protection assures that the boiler will not have return water below 140F.

    True, but with proper design of your system the boiler can provide 160F+ water to the system even with a cold storage tank.

    I simply boxed in my tanks with a combination of 2" foam and fiberglass, not less than R40 all around. Heat loss is very small, and since the "box" is in the heated space, nearly all heat loss goes into the heated space anyway.

    Knowing your heat loss and your minimum usable hot water are very important. But with all that said, I would go with 2000 gal with your large boiler. My 140,000 btuh maximum boiler handles 1000 gallons very well. Due to long burn times to charge a 2000 gallon tank, I would not go that large with my system. But your higher output boiler would make 2000 gallons reasonable. I am familiar with a Froling system, 170,000 btuh maximum, that has 1600 gallons of storage, and more would have been usable and practical in that system if space had been available, although the 1600 gallons works very well.
  10. stee6043

    stee6043 Minister of Fire

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    I'm not aware of a system that can provide a useable temperature window of 140 degrees. The actual calculation is not times "140" but rather times the useable temp window, "delta T" as you'll hear it referred to. For most of us this is going to be somewhere in the ballpark of 50 degrees. The difference between max acheivable temp and minimum effective temp. 190-140 is a typical range. Actual useable temps in 1,000 gallons of water in a hydronic system will never be 140 degrees. Useable BTU's in a 1,000 gallon thermal battery should be in the 300-400k range depending on configuration and actual temps unless you have very low temp emitters as some above do. But you're still nowehere near 1,000,000 useable btu's.
  11. logger6644

    logger6644 New Member

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    John, both you and JP base your calculations on a 60 temp differential. John you should use that 60 not the 140. In any event the useable heat storage is 500K per 1000 gallons. You need to burn in the neighborhood of 100 pounds of wood to generate this amount of heat. Don't know what your boiler holds but this will tell you how much you have to burn to fill storage. Remember also you are probably using while you are storing so you have to burn this additional amount if you expect to use the full capability of the storage.
  12. Nofossil

    Nofossil Moderator Emeritus

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    My $0.02:

    In general, more is better. That being said, in some cases there's a real advantage to being able to heat and draw heat from a smaller volume. When I'm heating storage from solar panels in the summer, I'm effectively using only the top 200 gallons of my storage tank. I'd get better performance if I had a separate smaller tank so that I could get higher temperatures in a lower volume of water.

    By the same token, there may be times when I'd rather heat 500 gallons by 40 degrees instead of heating 2000 gallons by 10 degrees. Stratification is your friend and can help mitigate this issue, but separate tanks are another bulletproof way to manage the temperature rise vs. volume tradeoff.

    For that reason my ideal storage setup would be a set of four 500 gallon tanks and a separate 200 gallon tank for storing solar hot water in the summer.
  13. goosegunner

    goosegunner Minister of Fire

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    Just a little info on what 100lbs of wood looks like.

    I dried a 13" diameter round of cherry that was 17" long in my nice warm boiler room. It weighed 46lbs and was 16% moisture when split.

    When it went in the building green it weighed 69lbs.

    gg
    711mhw and Karl_northwind like this.
  14. JP11

    JP11 Minister of Fire

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    Yup..

    I am getting a good solid 60. My storage will coast up into the 196 or so area. I see supply temps hitting 200.. And I calibrated that gauge this fall. I'll have to swap em and look again.

    I CAN let it get down to 135. My DHW is set at 132. In concrete radiant runs at 110. Staple up tries to run 140.. so 135 runs fine.

    I usually fire morning and night when it's convenient.. but the horsepower is there.

    JP
  15. heaterman

    heaterman Minister of Fire

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    Two main factors to consider and know before pulling the trigger.

    1 What is the total heat loss of all heated spaces at your outdoor design temperature?

    2. What is the minimum system water temperature at which your heating system can adequately supply the buildings being heated at the above mentioned outdoor design temp?

    Once you have a handle on those items you can determine the temperature "bandwidth" you system will be able to work with (30* or 50* or whatever) and then you can figure the water capacity needed to meet that for whatever time between firing you determine to be best.

    For example; If your heat emitters need to have 160* (fan coils or baseboard) water to crank out enough btus at your design temp you will need far more storage than if they can work all the way down to 120* (radiant slab)

    There is no standard answer for your question.

    If possible try to stay below a maximum temperature of 190 if you can. The lower the temperature at which you can operate your system the better because of the increased efficiency. You'll also leave yourself a little margin for "error" to keep things from going over temp (210*+). Also consider that very high water temps can accelerate corrosion even in closed systems.

    When I design a system I like to try and make it work at the European standard of 165-170* max temp.
  16. Beerdog

    Beerdog New Member

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    Stee and Logger....

    Ya... that was a big error I made. I used the return temperature and not the delta in my calculation. I know better but the Gosling Black Seal rum got the better of me last night.

    John.
  17. infinitymike

    infinitymike Minister of Fire

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    Do you stick a 13" diameter round in the burner?
    I know there has been many threads on split size, but what size do you burn or what size should most gasifiers burn?
  18. goosegunner

    goosegunner Minister of Fire

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    No I use small splits mostly 3-5.

    The 13" piece was more of an experiment to explain to my OWB using friends why they burn so much wood in their huge Heatmor boilers. They load them full with a bunch of pieces like that nice and green with about 3 gallons of water per piece......

    It is also interesting to see the look on their face when I tell them on a typical day I burn 2-2.5 of those chunks in splits.

    gg
    711mhw likes this.
  19. willyswagon

    willyswagon Burning Hunk

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    I love doing that as well. I have my racks full of wood( about 3.5 cord), but then next to the boiler I place the wood that I think I will need to get me through the next 12 hrs. People with the conventional boilers or OWB, see it and say
    "Oh you're trying to dry it out before you burn it".
    "No I'm trying to see how close to the actual load for the next I2 hrs I can guess".
    They can't believe how little wood a gasifier will burn in 12 hrs compared to their set up.
    So far Ive gone through 3.25 cord since early Oct. Some of these guys have gone through 8 cord!
  20. infinitymike

    infinitymike Minister of Fire

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    What the heck am I doing wrong? I have gone through close to 6.5 maybe even 7. Since early October
    And your in CANADA!!
    I have burning Ash, Maple, Cherry and Locust. On average they have been c/s/s about 6-7 months before burning.
    I resplit every so often and it's any where from 22-28% mc.

    Actually I know of one thing that was wrong and that was the location of my supply and return lines of my WG into my primary/secondary loop. When I flipped them I saw a 25% decrease in burning to reach temps. So that means I could have saved about 1.75 cord. But that still a lot more than you considering our locations.
    There still is a problem with the locations of my supply and return lines of the 3 zones
    Maybe if I move them I will save another cord or so.

    I know there are a lot of other variables. For example size of house, insulation, type of emitters,
    Set point of t-stats and the list goes on.
  21. willyswagon

    willyswagon Burning Hunk

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    My house is small by most accounts 880 sq ft on each of the three levels. I keep the main @ 72*F and upper level @ 68*F, the basement is about 65*F and then if we are going down to watch tv we will turn it up to 70*. The garage is 660 sq Ft and is for the most part heated by the little bit of loss from the boiler. If it gets really cold outside I'll turn it up to 60 *F to get the floor dry after the cars melt off.

    I have no storage, so I play the heat load game. I'm getting pretty good at it. At times I think I'd like it(storage) for conveince, but after talking to some locals that have it, I seem to go through less wood.

    Since Oct I have had to relight about a dozen times.If thigs hold up I'll go through about 5.5- 6 cords.
  22. old wethead

    old wethead New Member

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    one rule of thumb is about 400 gallons of storage per 100k of btus ... or 4/1000 x btus you have .... just what I have seen for some manufactures...best way is to calculate it all out for how long you want to go between firings and how long you want to stay home the day you recharge your tanks...lol...
  23. old wethead

    old wethead New Member

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    o...and that would be a minimum required storage...more is better to a point...
  24. maple1

    maple1 Minister of Fire

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    I'm having a hard time judging my wood pile, but I think I'm close to willyswagons wood consumption. I'll measure what's left when heating season is over. I started with about 7 cord, pretty sure I'll have a couple left. I averaged around 7.5 with the old one - definitely burning less.
  25. infinitymike

    infinitymike Minister of Fire

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    How do you do that? For example, you know just how much wood to put in to heat the main floor to 72* and then run out again a few hours later when the house calls for heat again and load a few more in? and so and so on? Or do load enough in to last for 12 hours, which means you have a period of time when the t-stats are all satisfied and the unit will shut off and then relight when the t-stats call for heat again?

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