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Post in 'The Boiler Room - Wood Boilers and Furnaces' started by verne, Nov 28, 2007.

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  1. verne

    verne Member

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    anyone have any info on useing a propane tank for storage. How is this done?.I have actually found some good prices on 500 and 1000 gal tanks new and used .

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  2. Eric Johnson

    Eric Johnson Mod Emeritus

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    There's a guy named hot rod at www.heatinghelp.com (go to The Wall) who has a 500-gallon propane tank hooked up to a gasifier. He's kind of an alternative heating guru and a very helpful and knowledgeable guy to boot. Has an EKO 40 heating his shop.

    Basically, you just pipe it into your system so that the water from your boiler passes through the tank.

    How much they quoting you on a used tank?
  3. verne

    verne Member

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    $600 for 500 used $1100 new and 1000gal new for $1900. Still waiting for more local return messages
  4. Eric Johnson

    Eric Johnson Mod Emeritus

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    That sounds like a good price. The old rule of thumb is $1 per gallon. I'd settle for $1.20 a gallon at current scrap prices.

    Any idea what a 500-gallon tank weighs?
  5. slowzuki

    slowzuki Feeling the Heat

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    I bought my non pressurized stainless tank at 1$/gallon, double wall with some insulation between.
  6. verne

    verne Member

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    from what I found a 500 gal propane tank weighs 1250
  7. leaddog

    leaddog Minister of Fire

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    I paid 600 for a 500gal tank in working condition as I am using propane for back up. You might be able to find a tank that has a name tag that is missing or has been dropped. and then you can get it for scrap price. Those should be under 300. The amish around here buy them, threw them in a fire and then cut them up and make outside boilers. they take a 500gal and put a 300gal inside. They smoke but work. Here in Michigan it is VERY hard to find a tank that they will give a bill of sale. All the propane dealers have gotten together and won't sell them as there is more money in leasing. Then they got you on price. It's even harder to find a dealer that will fill your own tank but the price is alot lower. I paid .75 less a gal and I don't have to pay rent if I don't use 200gal.
    leaddog
  8. brad068

    brad068 Feeling the Heat

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    Check local farm papers. Farmers and dairy suppliers have old milk bulk tanks that the coolant lines leak and they usually sell the for scrap price. Food grade stainless (304) will last longer than any wood boiler and they even have insulation. My boiler is built into a 1500 gal milk tank that I bought for 900$.
  9. verne

    verne Member

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    what are the pro's- cons pressure tank vs. standard storage. I kind of like the idea of no hx ,stagnent water etc.
  10. Nofossil

    Nofossil Moderator Emeritus

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    A pressurized tank may be a better solution as long as you're only using it for heat storage / retrieval. If you want to add secondary sources / sinks, then a sealed tank present problems as it's very difficult to install heat exchangers. For example, my tank has a heat exchanger to preheat my domestic hot water and another to allow the tank to be heated with solar panels. That forced me into an unpressurized tank, although I could have used additional pumps and external flat-plate heat exchangers as an alternative.
  11. verne

    verne Member

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    what do you guys think about a 1000 gal propane tank with an eko 40 .also what kind of pressure would i be looking at 2-3 pounds? I have neighbor with propane bussiness he has a new tank with apin hole at the top weld . getting close to breaking him ,dont want to push too hard without a need.
  12. Nofossil

    Nofossil Moderator Emeritus

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    I know that people have used propane tanks, but I don't know what pressure they're rated for. Usually, boiler systems run at pressures up to 30psi, so the tank would have to be good for that plus a safety margin.

    Also don't know if there are corrosion issues with the type of steel used or with the amount of dissolved oxygen in 1000 gallons of water. Anyone else have a better idea about whther any of these might be real issues?
  13. verne

    verne Member

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    Is a closed 1000 gal much different than an open storage. Nofossil I see you have 880 with the eko 25. At this point I have only oil boiler and side arm to suply. so I think in light of the price I would be better off with a pressure system other than none at all? What do think?
  14. Nofossil

    Nofossil Moderator Emeritus

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    Open or closed would be the same heat storage per gallon. Closed would have no evaporation loss, so that's good. Storage is better than no storage, and bigger is generally better.

    I just have no experience with closed storage tanks of that size. I raised some possible issues - if no one validates any of them, don't worry. I just hate to say 'no problems' when I don't have first-hand experience.
  15. Eric Johnson

    Eric Johnson Mod Emeritus

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    I don't think the pressure would be a problem. I suspect those tanks are designed to hold a lot more than 30 psi. They're pretty standard fare where pressurized storage is concerned.

    As to corrosion, I don't see where propane tank steel would be any more susceptible than boiler plate, but that's just a guess, based on the above.

    On the other hand, why would the propane company stop using a tank and basically sell it for scrap if there wasn't something wrong with it? Hopefully there is a good way to determine its integrity before you buy and install it, only to find out that it has a fatal flaw.
  16. leaddog

    leaddog Minister of Fire

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    The propane co. pull the tanks out of service when they get rusty or the paint gets chipped to bad. It cost to much to have them powder coated, to make them look good. By that time they are getting old and the asme stamp ususlly is getting hard to read. If the tag is gone or damaged they can't fill them. I think that they are tested to over 200lbs but I'm not sure just how high. The guy I got mine from was using it for a air tank at 200lbs and had been using it for 15 years. He said that if he hadn't used the air for a couple days it would still smell of propane. The only point you have to watch is you will need a large exspansion tank or leave the top so you would have room for exspansion. Zennon at New Horizon recommends them at his site.
    If there is a pin hole leak in that one they can't weld it and use it for propane but if it is a problem you could get a good welder and weld it and it would be fine for storage. I say go for it.
    leaddog
  17. verne

    verne Member

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    lead dog, that's exactly what the propane guy told me. He said the leak is so small it probably would fill with rust and be no problem. they test tanks over 200lbs. Zenon emailed me and said the same thing about expansion.the only problem Ive had is the propane guy sells heatmore , so access to hunt my property is payoff. thanks for all the help everyone. Im going to need alot more as I move along. Time to price the barn .Storage room getting bigger to hold a 16' long tank. I'm a carpenter so at least I have a clue with pole-barns.
  18. Nofossil

    Nofossil Moderator Emeritus

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    Sounds like a go - excellent! Don't scrimp on the insulation. A house has maybe a 70 degree difference between inside and outside. With the tank, you're looking at more like a 170 degree difference. I missed a couple of posts - did anyone talk about sizing the expansion tank based on the extra volume of water in the system?
  19. verne

    verne Member

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    I was told I needed larger expansion but not how large.also would you use laddomatt 21. If so how do you wire it to go on off auto?
  20. BrownianHeatingTech

    BrownianHeatingTech Minister of Fire

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    Okay, it's been a while since I've done this (I typically deal with non-pressurized storage tanks, so my expansion tank sizing is usually for the heating loop itself)...

    If I'm using the chart correctly, you have an expansion factor of 0.0351 (assumed for a worst-case 40-200 degree reheat).

    So, if you have 1000 gallons, that means you need a tank that can accept 35.1 gallons. Of course, you want to size this for the whole system, not just the tank, so add the fluid volume of each boiler, and a few percent more for piping. It never huts to over-size an expansion tank, except when you have to write a check for it... (let's call it 40 gallons, for the sake of discussion)

    I'm assuming that you'll go with a non-bladder tank, due to the cost involved with a bladder tank of the size you'd need...

    You typically want to size your expansion tank to never fill more than 2/3 with water. And you're going to have some water in the bottom under "cold" conditions, to make sure that the air doesn't leak down into the main tank. So I'd suggest at least doubling the acceptance volume when sizing the tank. Find an 80-gallon or larger tank, and use that. I think a used water heater would likely be a good choice. You can mount it above your propane tank, connecting to the "drain" tapping at the bottom. Do yourself a favor, and have a valve immediately after the connection to the propane tank, so you can isolate the expansion tank if needed for service.

    You'll want to use a tee fitting there, add a valve and then a barb adapter facing up, and the same at the top, but with the barb facing down. Connect a high quality (don't skimp on this) nylon-reinforced clear hose between these two barbs, and double-hose-clamp each connection. This is your "sight glass" which will let you monitor the tank. The valves let you isolate it, for periodic replacement, if it hazes or leaks.

    You'll have to pre-charge it with compressed air, so that's what the extra tapping on the top tee is for - add a valve, then a tee with a pressure gauge, then another valve and an air adapter of some sort (that's up to you). When you are filling, wait until you see water entering the bottom of the sight glass, then start adding pressure. You want to keep at least 10 gallons of water in there, so make a mark roughly 1/8 of the way up. Add pressure as you fill, making sure not to add enough pressure to push the water below that line. Make another mark 1/4 of the way up, and make sure the water ends up below that (this is the cold fill - it's going to go up as it heats). Record the final air pressure (do it on scrap paper, then when you've run the systen a while and are confident that things are set right, mark it right on the tank with a Sharpie).

    Since it is a non-bladder tank, the air will slowly dissolve into the water, so keep an eye on that sight glass. Get used to how the water level raises as the system heats, and mark the initial "high" water line, the first time you fully heat the system from cold. As the air is absorbed, that's going to creep up. Keep a decent safety margin, and periodically drain some water and add some more air. This is what that valve on top of the propane tank was for - close it, then you can drain the expansion tank and re-adjust it without fighting the pressure in the main system. Drain it to that 1/4 mark, and re-pressurize the air to the previous pressure. Then re-open the valve on the propane tank and you're good to go.

    Joe Brown
    Brownian Heating Technology
    www.brownianheating.com
  21. leaddog

    leaddog Minister of Fire

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    I was wondering about oxygen being absorbed from a non-bladder tank and is it a problem in a closed system. Would it be better to charge the tank with nitrogen. If you used nitrogen would it desolve in the water like air does .
    leaddog
  22. BrownianHeatingTech

    BrownianHeatingTech Minister of Fire

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    Nitrogen will dissolve, as well. It won't cause corrosion when it does, so it is beneficial in that way. I'm not certain, but it might dissolve quicker than air.

    And yes, having dissolved air in the system can cause issues, aside from the corrosion. It can bubble out and air-lock components, so having a microbubble resorber (eg, Spirovent) is very important. Actually, it might be beneficial to actually use multiple resorbers, in critical locations, depending upon the design of the system.

    Joe
  23. Grover59

    Grover59 Member

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    I will be building my tank in the next few days, I have decided to use the wood approach with an EPDM liner, this will fit my location well. The tank size will be 6’ wide 6’ long 4’ high I will be using a flat plate heat exchanger to charge the tank. I will not have any heat exchanges in the tank, I am basically going to pull out of the bottom of the tank and then dump back into the top.
    I will be using a completely separate loop to take the heat back out of the tank, I will pull out of the top of the tank to water to air floor or kick heater and then back to the tank. My thoughts are I will be able to pull more useable heat out of the tank with the forced air through the heater.

    Any thoughts or ideas

    Steve
  24. atlarge54

    atlarge54 New Member

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    Storage with water looks complex and expensive, expansion, corrosion, etc. Has anyone tried an insulated box full of pea gravel with a pex loop inside? Seems like it would eliminate expansion problems and pex seems pretty darn cheap to me. A crude estimate tells me a 4' or 5' square cube could replace 1000 gal water. I've got less than $3000 in my entire system (no storage). Bought junk Global hydronics OWB $300 wrapped firebox in copper tube replaced water jacket and filled with pea gravel for thermal mass. All this runs through a side arm heat exchanger for domestic hot water then to a pex floor radiant system with a small water to air exchanger for really cold days. Oh and I don't use the blower on the OWB the aquastat set at 130 F only opens the air supply. That blower on the OWB looks like a HUGE WASTE of heat out the chimney. I,m only heating a modest home so this system isn't for everybody. I've had a fire going every day for about 2.5 years now winter and summer. The boiler is off more than it is on. Pex in floor radiant is great I highly recommend especially for new construction.
  25. Nofossil

    Nofossil Moderator Emeritus

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    Been a while since I've done the math, but water has at least five advantages:

    1) More BTU storage per cubic foot, despite being lighter than rock.
    2) Convection means that HX coils can easily access heat from water that's not near the pipes.
    3) You can pump the heat storage medium itself if desired.
    4) Thermal stratification happens much more readily - gives a higher outlet temperature for the same average temperature.
    5) Easier to service if there's a problem.

    You're right that these advantages come at a price, and rock piles are a reasonable piece of the puzzle when designing heating systems. However, water was a clear winner in my situation at least.

    I'm completely with you on radiant heat, by the way.
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