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Heat Source for radiant heat

mdxers11 Member Posts: 2
I am adding a radiant pex system before basement finish for a 350 sq ft dining room, and 350 sq ft kitchen on the main floor. House is already heated with a 5 ton and 3 ton geothermal system with hot water tanks (81 gallons each) supplying the house from the geothermal. The 3 ton unit is used for the part of the house I am installing the radiant floor. We desired additional heat in the dining room and kitchen as there are a lot of windows and we have wood floors. With the square footage being under 1000 for the floor, would I be better off using the water heater as the heat source for just the floor, and installing a tankless to supply that part of the house with hot water? My reasoning is because of the shower and jacuzzi in the master, we do run out of hot water in the morning. We cannot fill the tub and use the shower for very long. I was thinking of going tankless for the hot water needs, and using the existing geothermal/water heater combo for the new floor heat. Thanks for any direction.


  • Gordy
    Gordy Member Posts: 9,546
    edited March 2018
    Well it’s appears there is a problem with sufficient DHW.

    Tankless WH need to be sized correctly for the loads, and temp rise, or they are disappointing.

    What is the present geo tank storage temps?

    Also I’m assuming your radiant floor panels are tubing below floors? What is the design detail? Suspended tube? Staple up? Plated tube? They all require different water temps. This is also considered in how much r value the floor has. 3/4” sub floor, and wood flooring. Is wood flooring engineered, or 3/4” solid?

    Wood floors per manufacturers recommendations limit floor temps to 82 degrees. So now what’s the load to the rooms in question? Supplemental are the floors?

    One other thought is your geo tanks were designed for the existing load. Are they big enough to carry the load of the floors also?

    Just a few questions.
  • mdxers11
    mdxers11 Member Posts: 2
    I am stapling up 1/2"pex between joists to the subfloor. The subfloor is 3/4 Advantech high density flooring between I joists. Using double omega channel aluminum heat plates. Thin enough to staple through. I would think the existing tanks couldn't handle the load for the floor and the hot water in the winter, but perhaps for the floor @ 750 sq ft. I think they are set at 120 deg.