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HELP Conventional boiler for low temp slab setup

radude Member Posts: 1
Hi a few years ago I installed on our 600 sq ft main floor a closed pex 02 barrier loop system, four 240'(+-10') 1/2 inch loops into 1.5" thin slab concrete over plywood sub-decking. All the loops are spaced 8" apart. The finished floor over the thin slab is engineered flooring (specs not to exceed 90 degrees). I also have three 225' 1/2 loops in the unfinished basement slab, spaced about 12 " apart. We live in cold country Minnesota. Our insulation is new better than average heat loss. To make a long story short I had a heating guy working with me who abruptly left town $ (and us out in the cold ha). Anyway we have been saving again for a condensing boiler we are thinking triangle tube 110 solo and design in domestic hot water though it's probably not going to happen this year again. The cold is getting the best of us and my patient spouse is getting cranky. I think we need to settle for a NG conventional boiler (55000 btu output). Design a primary secondary panel with a mixing valve and keep our old domestic hot water. My question is this I am concerned about the set up of the low temp of the main floor of my panel and how to design it correctly without short cycling and condensing too. I have been buying parts pumps manifolds for the panel but my ignorance surpasses my ingenuity, once again, and I am stuck.
Thanks, any design or advice would be greatly appreciated.


  • SWEI
    SWEI Member Posts: 7,356
    First, did anyone do a heat loss calculation on the house?

    There are a few less expensive mod/con boilers available now that should cost only a hundred or two dollars more than a conventional boiler plus an ODR-controlled mixing valve will. I believe there's still a $150 residential tax credit for an Energy Star boiler as well.
  • Tinman
    Tinman Member Posts: 2,808
    I've seen lots of cast iron boilers work with low temp radiant panels without flue gas condensation, although not my preference. Piping and control strategy is the key. P/S or a 4 way mixing valve. Start with a load calc like SWEI said. Mod cons $100-$200 higher than a comparable cast iron boiler? I'm not doubting you, SWEI. I'm just not aware those??
    Steve Minnich
  • SWEI
    SWEI Member Posts: 7,356
    If you buy them right, the little Lochinvar CDN040 runs about $250-300 more than a 50k conventional boiler plus a Taco iSeries-R. Factor in the $150 tax credit and it should be an easy sale.
  • kcopp
    kcopp Member Posts: 4,397
    Here is another option. Where not condensing it will do better than cast iron.