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System suggestions for radiant floor in pole building

Kevin_in_Ohio
Kevin_in_Ohio Member Posts: 8
in Radiant Heating
Dear radiant experts:

I am looking for a suggested heat source (boiler, hot water heater, tankless) and mixing valve arrangement (if necessary) for my pole building.  I don't need anything elaborate (or too expensive), just something to keep it about 50deg during a northern Ohio winter day.  The building is 36x52 (1872 sq ft) with 14' high R19 walls (with 2-10x13 and 1-8x7 insulated doors), R38 ceiling, and R10 under the slab.  Nibco calculated about a 50,000 BTU heat loss when they made my tubing layout.

There is almost 2250 feet of (non-barrier, oops) pex in 9 - ~250' loops embedded in the 5" concrete floor.  I have a 550,000 BTU gas line available in the building.

When I had the building built a few years ago, my intention was to use a tank hot water heater (hence the non-barrier pex), but I am having second thoughts.  A good tank water heater approved for space heating (i.e., Polaris) costs almost as much as a boiler.  I have also considered a Takagi tankless, but they don't seem too popular on this site and it seems like I will need two circulators and a mixing valve since there is about 20' of head loss in the heat exchanger.

Does anyone have any suggestions for a reasonably priced arrangement for my building?

Comments

  • MikeG
    MikeG Member Posts: 169
    Just curious

    Did Nibco recommend non barrier PEX at the time?  Since you have non barrier PEX you should separate the boiler side from the loop side with a heat exchanger. You'll need all non ferrous components on the loop side, pumps, valves ec.  Is it planned for all the loops to be on ot one time and at one temp?  Are all the loop lengths fairly close in lemgth?  If so it fan really simplify your controls and components.  Go with a boiler. The most efficient you can afford in the size you need.  If you are thinking of only heating sections, look at a modulaing boiler which will be able to modulate down to only a few loops if needed.   I'm no expert on this but have three friends in Northwest Ohio who have installed radient in slabs.  I was just an interested bystander.  Two are farmers with large pole barn shops.  One is going to use a wood or corn pellet stove boiler, the other is using an outdoor wood boiler which is also heating his house and the third built a house and shop combined pole type structure on a slab and is using a wood gasification boiler.  He also has some large storage tanks.  They are all in various stages of getting them set up. 
  • Alan (California Radiant) Forbes
    Alan (California Radiant) Forbes Member Posts: 4,206
    Heat Source

    Down and dirty: 75 gallon water heater.



    http://www.pexsupply.com/AO-Smith-FCG-75-74-Gallon-ProMax-High-Recovery-6-Yr-Warranty-Residential-Water-Heater



    Elegant and pricey: Prestige Solo with a heat exchanger for the non-barrier tubing.



    http://www.triangletube.com/TriangleTubeProduct.aspx?CatID=1&PID=1



    Out of this world: Use the Prestige Solo boiler along with an indirect tank that has two heat exchangers, like this one:



    http://www.viessmann.ca/en/products/speicher-wassererwaermer/Vitocell-B_300.html



    One heat exchanger would be used to heat the tank via the boiler for your domestic hot water and the other heat exchanger would be used to heat your space.
    8.33 lbs./gal. x 60 min./hr. x 20°ΔT = 10,000 BTU's/hour

    Two btu per sq ft for degree difference for a slab
  • Gordan
    Gordan Member Posts: 891
    Prestige in an open system

    I remember reading here that the only thing inside a Prestige Solo that's not kosher for an open system is the circulator (and that's only inside the PS110.) That's not to say that it may not be a wise precaution to isolate the boiler with a FPHX, just that it may not strictly be necessary.
  • Kevin_in_Ohio
    Kevin_in_Ohio Member Posts: 8
    To answer your questions...

    Yes, since I planned to use a tank water heater, NIBCO recommended non-barrier PEX.  I agree that a cast iron boiler needs separated, but if it has a stainless heat exchanger I think I would be alright.  I was also thinking a hot water heater (tank or tankless) would be alright since I'm not sure that a closed system with non-barrier PEX is any worse than an open system.  I am planning to use non-ferrous pumps and valves.



    The loops are all within 10' of one another.  I have three manifolds located in separate parts of the building connected by 1" PEX so I could add zone valves in the future, but I think I'll be fine with a single zone.  As I said, it's only a pole building, so I'm not too concerned with temperature variation.



    I've considered a condensing boiler, and while I agree that is the most efficient, I'm not sure how much difference it would make since inside my building will only be about 20-30 deg warmer than outside on most days.  Seems like overkill to spend $3-4k on a boiler.  If it were my house and I was trying to maintain 72deg, I'd definitely go with a boiler.
  • CMadatMe
    CMadatMe Member Posts: 3,086
    edited November 2011
    X-Pump

    Need a HX no matter how you look at it. Not that I belive in a water heater to do a boilers job but if I was to have to use one I'd do a tankless and then a Taco X-Pump to separate the radiant from the domestic. The X-Pump will give you your injection pump, system pump and outdoor reset all in one..

    http://flopro.taco-hvac.com/products/index.html?category=345

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  • Kevin_in_Ohio
    Kevin_in_Ohio Member Posts: 8
    What about BW GX-2-25S6BN?

    Saw this water heater on sale at PexSupply.  Seems like it would be a good heat source: approved for space heating, 78k BTU, 2" insulation, only 25 Gal tank.

    http://www.pexsupply.com/Bradford-White-GX-2-25S6BN-25-Gallon-78000-BTU-High-Performance-Atmospheric-Vent-Residential-Water-Heater-Nat-Gas

    Also has side connections for space heating.  What are these for?  Seems like they just avoid having to run the lines up to the top of the tank.
  • SWEI
    SWEI Member Posts: 7,356
    HX required?

    Any reason he couldn't pipe a TT boiler direct and use a bronze circulator?
  • CMadatMe
    CMadatMe Member Posts: 3,086
    Don't Think So

    Please read the last line on page two of the spec sheet.



    http://bradfordwhite.com/images/shared/pdfs/specsheets/115-B.pdf





    Notice piping on page 28 below.. References Heat Exchanger.



    http://bradfordwhite.com/images/shared/pdfs/manuals/238-47656-00B.pdf

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  • CMadatMe
    CMadatMe Member Posts: 3,086
    Yes He Could

    No ferrous part sure.

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  • Kevin_in_Ohio
    Kevin_in_Ohio Member Posts: 8
    Why not?

    Here is the last few lines you referenced:

    Suitable for Water (Potable) Heating and Space Heating.

    Toxic chemicals, such as those used for boiler treatment, shall NEVER be introduced into this system. This unit may NEVER be connected to any existing heating system or component(s) previously used with a non-potable water heating appliance.

    Seems like it wouldn't be a problem to use this water heater since it is approved for space heating.  I don't think the antifreeze mixture would be considered a toxic chemical.

    Also, I see that the figure shows the space-heating connections, but I'm assuming they go into the tank in a similar manner to the domestic water connections at the top.  If I'm only connecting the side ports, do I plug the top connections?
  • CMadatMe
    CMadatMe Member Posts: 3,086
    Missing The Point

    Did you read page 28 pf the install manual and look at the piping diagram. Heating source is fed by a heat exchanger. Yes it can be used for heating if you install a heat exchanger.

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  • Kevin_in_Ohio
    Kevin_in_Ohio Member Posts: 8
    Heat exchanger

    I thought the heat exchanger was the space heating device (i.e., radiant floor).
  • CMadatMe
    CMadatMe Member Posts: 3,086
    edited November 2011
    Heat Exchanger

    The radiant would be a heat emmitter not a heat exchanger. This is a heat exchanger in your case the boiler is your water heater.



    http://www.gea-phe.com/typo3temp/pics/2a80d2144f.jpg

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  • SWEI
    SWEI Member Posts: 7,356
    heat exchanger

    Is there any potable water in this system?
  • Gordy
    Gordy Member Posts: 9,546
    Manufacturer specs.

       Should be adhered to, and Chris is right on calling it out. What may seem a gray area, really has a point. Suppose some day you decide to use the water heater for potable water heating, after using it for space heating with no heat exchanger. Its contaminated. Suppose you sell the property, and the next person decides to get a boiler sell the water heater to someone who will use it for potable heating. The scenarios go on.



       I'm not an advocate of water heaters ( tank, or tankless) for Space heating. I think the efficiency sucks, all though the up front costs may seem cheaper. In the end either through larger pumps, creative piping, and lower efficiencies your jumping over a dollar to pick up a dime. Will they work yes. Are they the best choice no.  Lots of threads on here of people trying to get water heaters to do a boilers job.





    Gordy



     
  • Kevin_in_Ohio
    Kevin_in_Ohio Member Posts: 8
    Its all potable water

    A non-toxic water-antifreeze mixture should be potable water.  I use it in my RV every year.  Sure, I'm not going to use Prestone like I use in my car.  As far as later purchasers, they can drain the antifreeze mixture (like I do in my RV every spring) and use the water heater however they want.

    If it's really a problem, I can skip the antifreeze.  I have a 17kw natural gas generator that will keep the circulator pump on in the event of a power faiulre.

    Boilers seem like a good idea if I need to heat water to a higher temperature for a radiator system, but heating water to about 120 deg has been the job of water heaters for decades.
  • CMadatMe
    CMadatMe Member Posts: 3,086
    edited November 2011
    Your Original

    Post asked the Pros for their advice. I think you were given the best advice by all of us that responded. The choice is yours but I don't recommend what you propose without the use of a heat exchanger. You can search this site for post similar to yours easily finding the nightmares and poorly operating radiant systems using a water heater. I think the quote at the end of my posts says it all. Best of Luck.

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  • Mark Eatherton
    Mark Eatherton Member Posts: 5,858
    You said....

    "Boilers seem like a good idea if I need to heat water to a higher temperature for a radiator system, but heating water to about 120 deg has been the job of water heaters for decades."



    Close, but no banana. A domestic hot water heater WILL condense its flue gas when exposed to long term condensation production potential, which is what you WILL be exposing it to. Expect a SHORT life expectancy, with lots of issues.



    The reason its not an issue when being used as a DHW heater, is because the loads only last about 1 hour per day, not ALL DAY long.



    Just because your Corvette can do 150 MPH doesn't meant its OK to run it that way all day long...



    You MUST protect the appliance from the potential of long term condensate production, or be ready for the consequences. Just because you CAN do it, doesn't necessarily mean its a good idea.



    Been there, done that, wish I hadn't, probably wouldn't do it again unless it was temporary and an emergency situation.



    Read my tag line as well....



    BTW, the corrosion inhibitors that are in non toxic glycol can be toxic to human beings...



    Proceed with caution.



    ME

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  • Kevin_in_Ohio
    Kevin_in_Ohio Member Posts: 8
    Will it really have condensation problems?

    Condensation occurs when the flue gas is cooled below the dew point.  If I have 120deg water leaving the water heater with a 20deg temperature drop, the returning temp is 100deg.  Seems like a pretty high dew point.  Per Wikipedia, dew points above 80deg can be deadly for some asthma patients.  I don't expect any dew points below 60deg this winter in Ohio.

    I agree that if this were an open system and I was filling with 60deg water from my well I could have a problem, but I just don't see it with a closed system.

    Finally, thank you all for your suggestions.  I don't mean to seem argumenative, but I just want to make sure that I am considering all options.  I guess that's just the engineer in me.
  • CMadatMe
    CMadatMe Member Posts: 3,086
    Rain

    Better use a stainless vent system because Mark is spot on. Because the htr will operate under conditions it normally doesn't see, your flue gases will be condensing all the time and all that nice acidic water will make its presence known. Dew Point beings when return water temps get around 130. No different then a condensing boiler.

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  • Gordy
    Gordy Member Posts: 9,546
    Low building temps

     You stated in OP that you only plan on 50* space temps.  Will this be at all times, or is there a usage pattern for the building? This could prove to be another monkey on condensings back.



    Gordy
  • SWEI
    SWEI Member Posts: 7,356
    outdoor reset

    If you're going to use a non-condensing water heater, you need to limit return temps the same way you would for a non-condensing boiler.  A mixing valve modulated by an outdoor reset controller would be my choice.
  • Kevin_in_Ohio
    Kevin_in_Ohio Member Posts: 8
    I was wrong, but...

    Alright, I was wrong in considering the dew point of the air.  The dew point of the flue is more like 130deg, as you stated.  However, I still wonder if there will be a condensing problem.  Haven't most boilers been non-condensing for a while now?  I expect the temperature of the flue gas will still be quite a bit higher with an 80deg efficient water heater.
  • CMadatMe
    CMadatMe Member Posts: 3,086
    Do What You

    Wish. I think you have received more then enough advice to make the right decision. By your posts it seems your trying to grasp at any straw that will get you into the water heater. Your the engineer so you must know more then all of us here who have been designing and installing radiant and other high efficiency systems. In my case for more then 20 years others maybe even longer. I don't think any of us would be giving you the best advice if we condoned what you want to do.



    My car will work with 15lbs of tire pressure but at what expense?

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