Boiler for Radiant Slab Pole Barn

Discussion in 'Boiler Forum' started by Reicherb, Oct 16, 2020.

  1. Reicherb

    Reicherb Member

    Joined:
    Nov 7, 2013
    Location:
    Linden, MI
    I have a new 30x40x14 barn that has lean tos that could be enclosed some day bringing the square footage to 50x40. It's got 2" foam under 5" concrete. The ceiling will be blown in insulations. The walls will be spray foam. The overall 50x40 space has nine 1/2" loops for a total pex length of 2000' ft. I'm in central Michigan and am looking for a natural gas boiler to heat the building. I may eventually have domestic hot water as well.

    Can you please help me select the correct boiler or perhaps an on demand water heater if that is a viable option.

    Thanks,

    Brad
     
  2. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Joined:
    Sep 2, 2004
    Occupation:
    Retired Systems engineer for defense industry.
    Location:
    New England
    It's probably not a bad idea to pay an engineer to calculate your actual heat load. Most heating contractors will way oversize the boiler which can lead to less comfort, reliability, and higher equipment costs. They will take into account the exposure, windows, doors, insulation levels and your zone.

    Is this all going to be one zone? Some suggest a maximum length loop of 200', so you're a bit higher than that. One zone, versus more will dictate the pump(s) needed. Don't oversize it for the use of domestic hot water unless you expect to be needing huge quantities for extended time frames. A bit for a shower or home kitchen an indirect on a priority zone is nearly always sufficient since the slab will have a lot of mass, diverting heat to reheating water in the indirect is not an issue.
     
  3. Sponsor

    Sponsor Paid Advertisement

     
  4. Reicherb

    Reicherb Member

    Joined:
    Nov 7, 2013
    Location:
    Linden, MI
    The main building has 5 of the 9 loops. It will all be one large open space. Some day there may be an open loft in part of it. The other 4 loops will eventually be enclosed into 4 10x20 rooms. 1 or 2 soon and the other two, years down the road. There are 4 3x3 windows and two 12x14 insulated overhead doors.

    This will not be living space. It's a shop. I intend on generally heat it to 40-60 degrees (maybe 70 on a rare occasion) depending on how I'm using the space. The domestic hot water is for a half bath in the building as well as a utility tub. I don't expect frequent use so having some form of domestic hot water is great but not worth adding much to the cost.

    In the future, I could turn one of the 10x20 rooms into a man cave living space.

    I'm already above my budget on the project so paying an engineer seems like a last resort. I was able to spec and install a boiler for my home using help from this forum a year ago and I'm very happy with the way it turned out. My home is more comfortable and my utility bills went down.
     
  5. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Joined:
    Sep 2, 2004
    Occupation:
    Retired Systems engineer for defense industry.
    Location:
    New England
    You need to know the ceiling area, the wall area, the exposure, the infiltration rate, the R-factor of your insulation and the area and U-factor for the windows and doors...there are calculators that will let you input that sort of information that are free, but to get a better result, you need to often pay for a better answer. Then, you need to know your local degree-day heating requirements and your design temperature. Keep in mind that a slab like that will have a huge thermal mass, so any changes you want to make will require quite a long time, often days to make a radical change...it's not like bumping the thermostat up on a forced air system...or even radiators, you are trying to change the temperature of the entire slab. Generally, people will be more comfortable at a lower temperature with a radiant floor than other types of heating. MI can get frigid.

    You will also need to know the spacing and length of the loops to determine how much energy transfer is even possible. You don't want it to require a super hot floor, as that's not comfortable nor is it very efficient. The slab will have issues if you try to get it too hot, and the pex won't like it either as it will be expanding and contracting more if the delta-T is high. Generally, the actual delta-T isn't very big in a slab, so that isn't an issue at all.

    You need to look at what the minimum return water delta is allowed on whatever boiler you choose, as that can be radical, especially on startup from cold soaking. A condensing boiler can generally handle fairly cold return water, but you do need to keep that in mind.
     
  6. Reicherb

    Reicherb Member

    Joined:
    Nov 7, 2013
    Location:
    Linden, MI
    This is a pole barn. I'm not looking for residential comfort. There must be a typical situation that would apply here.
     
Similar Threads: Boiler Radiant
Forum Title Date
Boiler Forum Radiant floor heat boiler overpressuring and blowing steam Oct 1, 2018
Boiler Forum Boiler for Radiant in ICF Oct 30, 2017
Boiler Forum Radiant floor heating boiler room plumbing layout. Feb 4, 2016
Boiler Forum Radiant floor, Boiler + 80 gal. Buffer, system works great. Nov 7, 2013
Boiler Forum Radiant Heat, Pex Supplier, Parts, Outdoor Boiler Insulated Line Aug 17, 2012

Share This Page