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Considering retrofitting radiante heating in basement joist bays

Ken1 Member Posts: 18
Hi Everyone,

I am considering switching over from a forced hot air system to a hydronic heating system. I have been thinking about doing radiant heating in the joist bays of my basement and putting in wall panel radiators in my second and third floors. I have a very good plumber who will do the major work, but I want to keep costs down and have been considering doing the staple up pex in the basement joist bays myself to keep the labor costs down.

I'm wondering a few things:

1) How thick can my flooring be and still have the radiant be effective and work well? How can I figure out just how think my flooring is?

2) What are the best companies/products out there for the staple up systems?

3) I'm a pretty handy guy, my basement has open joist bays with a few obstacles to work around and high ceilings (about 9 feet). How big of an undertaking is this? I have approximately 750 square feet of floor to do.

4) If I am considering redoing the floor in my kitchen, is it better to put that section of the radiant pex above floor boards and below the new floor instead of in the basement joist bays? If I am not quite ready to do the kitchen floor quite yet, can I do it in the joist bays now and switch over later (in a few years)? Or is it just better to do it all in the joist bays?




  • Gordy
    Gordy Member Posts: 9,546

    First thing you need to do is a heat loss of the home, room by room. You need this information to determine IF under floor radiant can heat the space, AND what size panel rads for the rooms in the upper floors.  You also need the heat loss to determine flow rates, and water temps to all the above emitters. Also you will need this info to size the boiler for your hydronic system. MOD?CON recommended, and there in running the lowest water temps to the emitters possible.

     To determine floor thickness find an inconspicuous area, and drill a hole from the basement up yhrough the floor, or there maybe a spot that this has been done where some mechanicals have been run.

     For the kitchen do a sandwich install. The less r value between the tubing, and the space you are heating the better. Use extruded plates for either install they are a must if you are going to get the most output out of either type of floor heat.

     Insulation is a must also.

  • Mplsavant
    Mplsavant Member Posts: 20
    I'm a homeowner who has done both....

    Our sunroom, we retro-fitted with the wirsbo tubing in the joists with the aluminum type insulation underneath the wirsbo.....the sunroom floor was tile, we live in MN.  The basement slab in that house and our current house both have wirsbo in the slab.....it is really night and day....the sun room was fine but when you walked on the slab or the stained concrete in the bsmt, it just felt nice......if it is your only option, might still be worth it.....just a matter of the sub-floor, flooring, etc, etc I suppose.  Hope that somewhat helps.
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