Thermal storage Qs, PEX vs Copper; bleach in non-Pressu. tank; Flue and boiler sizing

MapleFoxFarm Posted By MapleFoxFarm, Jan 5, 2019 at 12:36 PM

  1. MapleFoxFarm

    MapleFoxFarm
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    First time post here!
    This site is really great, learned a whole lot already.

    I'm just about to pull the trigger on an EKO 25 kw - 85k btu (gasifier), and incorporate a thermal storage tank. This system would run in parallel to a very tired propane boiler from the '80's. My house is moderately well insulated, (very old farm house renovated in the 1980's), 1150 ft2 but will add another 400ft2 in the next few years and has 2 zones of baseboard hot water radiators.

    I have a father in law who is a master plumber and I'm a DIY kind of guy who likes to learn about things and save money. So I think we can get through this cheap, safely and correctly.

    1) My first question is, can I use oxygen barrier PEX instead of copper tubing for heat exchange in a non pressurized storage tank? (Cost savings)

    2) I mostly hear that you can't have too much thermal storage or people often say bigger is better than smaller (in this case). However, the other day I was reading something that said don't over-size your storage because your boiler won't be able to keep up.I used a calculation found online which said the max should be about 660 gal. for the EKO 25 but then I saw a guy on this site (can't remember where, that had an EKO 25 with 880 gallons, thoughts?
    I also used another calculator that was very general based on cubic meters of inside of a building/house and figured that with a moderate insulation rating I would need at least a 13.6 kw boiler for my house (the EKO 25 is of course 25 kw). What are the physics/considerations of storage sizing and over sizing?

    3) I heard you can get algae buildup in a storage tank which may reduce heat exchange efficiency between storage water and coils. Is this true? If so, could I put bleach Bleach in the storage tank?


    4) I see very conflicting numbers on what the flue size needs to be for any given size boiler. For instance the EKO site says you need 8"ID for the EKO 25 (85k btu) but it also says you need 8" for the EKO 40 (137k btu)! This lead me to believe that there was more to it and, there does seem to be. I read that you need 15-20 Pa in the chimney for the EKO line or so many cubic units of space in your chimney per number of btus and the calculations are quite complex if you try to figure these out on your own. Yes, the manufacturer says use 8" but per the example above, it seems like you might not need that much. I did run the max BTU, cross-section of chimney and Pa calculations on my own and they all showed 6"ID would work but I'm not an engineer so I'm not certain my math is correct. I already have a 6"ID metal bestose chimney running through the inside of my house for good draft and recovering heat off the chimney. It's currently hooked to a 602 Jotul, great little stove. The chimney height will be about 23' when I run it into the basement for the EKO with just 2' exposed to the outside air at the top.
    Anyway, has anyone run a 6"ID chimney for an 85k btu boiler or know of an online calculator that is relatively easy to use to tell if I'm getting 15-20 Pa of draft?

    5) Last question: My buddy is offering what I think is a good deal, $3,000 on an EconoBurn 150,000 btu, 5 year old boiler. I certainly don't need this much boiler but can I just partially load the boiler if I don't need that many btus or does it not work that way? Or maybe have 1,000 + gallons of storage and then fill it and then just run off the thermal storage for 2 days?

    Thanks for any information folks may have out there and stay warm! ;)
     
  2. Bad LP

    Bad LP
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    5) You may want to think more about that. HWBB has a higher design temp. It works on lower water temp but the zone runs for a very long time. This could be a problem when your storage temp goes down and you are getting near the end of your run of BB.

    My own BB runs are short and home run to a manifold. I think my longest run is about 18 feet of fin. I really want to install panel radiators so the lower temps will work better.
     
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  3. MapleFoxFarm

    MapleFoxFarm
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    Hey Bad LP, thanks for the reply! So I think I'm missing the point here, are you saying don't plan on oversizing the boiler and then run off hot water storage for a few days bc BB requires higher operating temps which would probably dip below requirement before the end of the two day period? Would i go with the smaller unit and fire it probably twice a day or go with the big unit and fire once a day? Or neither of those? :)
    Thanks!
     
  4. gfirkus

    gfirkus
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    I don’t have open storage, but i think you want copper in your storage do to heat transfer. Heat transfer on pex isn’t very good.
     
  5. TCaldwell

    TCaldwell
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    Possibly you could do a heat loss on your house and compare that to the amount of existing baseboard you have. Sometimes a builder will err on the side of excess, if this is the case you will be able to heat down to a lower supply temp.
     
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  6. maple1

    maple1
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    Some overthinking going on here.

    Main consideration on storage size is how long you can or want to go between burns. Minimum size would be big enough to store the heat from boiler full of wood, starting with depleted storage.

    Main consideration on boiler size is how often you want to feed it. Minimum size should be comfortably above max heat loss.

    And storage being too big because boiler can't keep up is a crock of hooey. As long as storage is within the heated space.
     
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  7. Bad LP

    Bad LP
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    I'm saying to go with the largest boiler (within reason) you can and as much storage as you can fit. With BB I think you are going to want to run on the higher end of the temperature range with such long BB runs. A 20::F drop starting at 180 in one thing. A 20::F drop starting at 120 is another. Obviously my own zones being short runs has the zone valve open for a much longer time when my tanks fall to 120/130 to satisfy. If the entire 2nd floor only had 1 zone versus the 4 it has I'm rather sure I'd be unhappy.

    I'm also disappointed in making domestic hot water with the boiler. I will be taking that off and relying on the System 2000 to provide it. I swear that zone rarely closes. On the plus side I could not be happier with the wood boiler on the radiant floor heat zones.

    As mentioned above a heat loss calculation is a good place to start. I knew going into this project my boiler was on the edge. It's fine for temps down to around 10::F. At zero I'm filling it more than expected by around 1/2-3/4 of a load per day but it's still better than burning all that propane.
     
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  8. maple1

    maple1
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    It is also quite often fairly easy to add more finned length to existng baseboard.
     
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  9. Fred61

    Fred61
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    I just removed an EKO 25 and 500 gallon storage after 9 years of service. It's sitting here waiting for someone to buy the package off Craig's List. I accomplished it just in the "knick of time" since I have become increasingly disabled in he last three months.

    EKO resized.jpg Inside tank resized.jpg storage resized.jpg

    I didn't know what to expect when opening the tank after nine years but was pleasantly surprised to find the water crystal clear with a thin coating of sediment on the bottom presumably from some oxidation of the copper.

    The house is 1100 sq/ft 1970,s ranch so similar in size to your place. I'm sorry I'm not able to provide you with any numbers for heat load because since I downsized to this "retirement" home, it's been a "work in progress" weatherizing, insulating and installing radiant. I know I have a pretty efficient building.

    I burned +/- three cord of DRY wood each season. My burn schedule was: One fire per day lit around 4:pm and the tank was pretty well charged to 180 by about 7:30 to 8:00 PM. Time varied depending on storage temperature and whether the zones were calling for heat. When storage reached 180 degrees I shut the boiler down. It took a little "seat of the pants" calculating to load the correct amount of wood in order to have just a few chunks of charcoal to light tomorrow's fire. Some remaining charcoal was important because a couple pieces made the difference between a 5 minute re-light session and a 20 minute session using kindling and small splits.

    The storage at 4:00 PM on normal winter days would run about 140 degrees.

    EKO is asking for an 8 inch flue because that's the size of the collar and that's the only reason. The reason it's 8 inches is because that's what they have on the shelf. Use the same collar for all models. You will be better served to reduce to 6 inches. I reduced to 6 in. within 2 feet of the collar and fed into a 6 inch Metalbestos chimney about 30 feet finishing about 3 feet above the ridge. I'm one of the few on this forum that actually produced photos of my unit aggressively burning with the door open and not smoking up the room.

    There was something about the Jotul 602 that made it probably the most efficient and hottest and clean burning stove ever. They tried to build the little rascal in larger sizes but failed every time. There's something about the shape, size and air flow that's perfect.

    I have several posts here over the years that you can access tht may shed some light on my burning experiences with the EKO. You might need to filter out some of the stupid comments and wise a$$ remarks.
     
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  10. maple1

    maple1
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    Best wishes, Fred.
     
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  11. MapleFoxFarm

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    So basically I could go with an oversized boiler (relative to heat loss calc) and as long as I had plenty of storage I wouldn't be wasting energy bc it's all getting stored in the water?
     
  12. salecker

    salecker
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    I have an Econoburn
    I would buy one again,unless i was looking for one with computer controls.There are more efficient boilers than the Econoburn i have heard,but where i am having a bulletproof simple boiler is better suited.I am 100 miles away from any parts or anyone that could work on my boiler.A few years ago my controller died and i was able to keep using the boiler by wiring it to a plug that i would plug in to run the fan and pumps,using the high limit aguastate for shut off.
    The Econoburn is pressurized.I also did all my work myself,including building storage from 2 500 gal propane tanks.I have room for 2 more,and may add them some year.Right now my priority is to add a solar to the mix so i can go the shoulder seasons without burning anything.
     
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  13. MapleFoxFarm

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    lol, jeez, i was so focused on surface area to volume ratio and cost that the obvious slipped right under my nose! Good point, thank you! Though this isn't good news for the budget :rolleyes: :)
     
  14. salecker

    salecker
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    Correct
    Your storage will also act as a dump zone for your boiler.You will get some loss from your tanks,boiler and piping depending on how well you insulate everything.
    My complete system is in another building,this is for my house insurance which i don't have,mess and smoke the boiler building started out white and is slowly turning darker grey,absolutely no chance of carbon monoxide poisoning,
    Both my daughter and xwife had asthma,so it was a no brainier to build the way i did,plus i have a heated workshop for my hobbies 24/7.-40C here this morning,that means a longer burn today to keep up. even after 8 yrs the 125ft walk to deal with the boiler really isn't a big deal when you look at the trade offs.
     
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  15. salecker

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    I have heard of people using cast iron rads for heat transfer in storage,or other copper rads could be used as well.If you are a DIY'er you should be able to come up with something cheap that will work as good as copper tubing.Spend a couple of hours walking around some scrap yards.
    Or buy Fred's system,then you have an expert to help you as well.
     
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  16. MapleFoxFarm

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    Fred, thanks (again),
    I say, 'again' because we actually talked through craigslist about your set up several weeks back! My name is Trevor from near Montpelier. I would really love to buy your system but as we discussed, i can't get that tank into my basement and it sounds like a lot of folks are saying don't put your thermal storage in an out building bc of heat loss. Thanks for all the real world operating specifics on the EKO 25. Much appreciated.
     
  17. MapleFoxFarm

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    I just found some cast iron radiators on CL. Thanks for the idea! Also, whoever renovated this house in the '80s over-ordered the BB radiators with the fins on the pipe I think there's about 25 feet of that in my barn. I'm sure i would need more but i also saw some of those on CL fairly cheap.Think that would work?
     
  18. MapleFoxFarm

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    Has anyone used baseboard radiators inside a non-pressurized tank? Not sure I'm using the right terms, so when i say BB radiator i mean the copper piping with the metal fins on it. I have some that were in the barn when i bought the house.
     
  19. Bad LP

    Bad LP
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    You are going to need a powerless dump zone and that unused fin tube will be perfect for it if you have enough of it.
     
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  20. MapleFoxFarm

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    Oh right, i forgot about that part...good thing the father in law is a plumber, he'll catch the stuff i miss.

    Does the dump zone have to be gravity feed/below the "water out" from the boiler level?
     
  21. Fred61

    Fred61
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    You might want to do some research on putting aluminum in the storage tank. Could be some reaction. I made sure there were no other metals besides the stainless tank and the copper coil.

    I have a 100 feet + of fin tube I've been looking to get rid of. Being rigid you will have
    several solder joints within the tank.
     
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  22. maple1

    maple1
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    Not to slight your FIL by any means, but not all plumbers are totally up to speed on hydronics and their intricacies. Just something to be aware of.
     
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  23. MapleFoxFarm

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    No, I hear you, but he has done a lot of different furnace installs, I'll have to talk with him some more once I feel like I have a handle on "the basics" here, to make sure he's confident with installing this type of system.
     
  24. tom in maine

    tom in maine
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    Some important stuff about unpressurized tanks. NO BLEACH. Please!!
    You will corrode heat exchangers and possibly damage the liner.
    Any algae will die off as soon as the tank is heated above 140F.
    There is no fouling of heat exchangers in tanks that are heated, even just seasonally heated.
    You should check the pH, especially in EPDM lined tanks, but a spot check never hurts. They should always be neutral to slightly basic.

    Using baseboard in a tank or aluminum coils is not great. They will corrode. Fintube offers no thermal advantage. They are water to air heat exchangers, not water to water. Use copper or stainless steel.
    PEX works but you need 4 to 6 times the surface area of copper to work properly. It is not worth messing with.

    My 2 cents worth.
     
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  25. warno

    warno
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    If I could add something just based on plumbing stand point. Read everything you can about keeping your plumbing as simple as possible and your head losses to a minimum.

    After fighting my boiler to heat my storage efficiently for one whole season I found out, from the help of this great forum, I had an undersized heat exchanger and overcomplicated plumbing. I had to replumb my whole system between boiler and storage and now it's running amazing.
     
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