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New shop in slab with boiler

I built a new pole barn and set it up with pex tubing in the slab and now its time to hook it all up. I have 1800 ' of 1/2" pex in six 300' loops connected to a Rehau manifold. I have a Munchkin T-50 boiler to supply the hot water. Now I need to know the best way to set it up. I planned on doing a closed system with a little anti-freeze in the water just in case the power goes out for an extended period. I'm just not sure if I can do a single loop or dual loop with closely spaced tees or add a mixing valve or what is best. I live in northeastern Oklahoma so it doesn't get too cold here but sometimes it does and I do mechanical work in this shop so Radiant heat sounded good! Just need a little help setting it up. The shop is only insulated with dbl bubble wrap and the slab was insulated with 1" foam under the concrete and the 2" x 6' board around the perimeter. Thanks for the help


  • Ironman
    Ironman Member Posts: 6,560
    That boiler MUST be piped primary/secondary as shown in its manual. The heat exchanger in it has a high head loss and it heats the water instantaneously going through, so proper flow rate is critical. You also have to use the proper size circ on the boiler loop that's spec'd in the manual.

    As far as the floor goes: a thermostatic (dumb) mixing valve is not the proper control for a slab because of its high mass. The floor water temp needs to be controlled based upon outdoor reset which the boiler can do if you have no other emitters beside the floor connected to it. The reset curve just needs to be setup properly.

    Was an accurate heat loss calc done on the building? It's the basis for sizing everything, including piping, pumps, determining water temps, etc.

    Bubble wrap has very little true R value despite some of its claims. You may want to add board or bat insulation if you want to keep your gas bill down. Proper insulation is a lot cheaper in the long run than fuel.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.