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radiant install - hardy board or self leveling cement?

lisi80 Member Posts: 3
We are installing hot water radiant in our kitchen and bathroom. The plan was to install viega climate panels for 3/8 pex on top of existing sub floor, hardy board on top and then tile.

2 questions:
1- should I use self leveling cement instead of hardy board?
2- should I use 1/2 pex instead of 3/8?

also - if self leveling or a cement is recommended - should I just lay down 1/2 plywood and staple the pex instead of using the climate panels?

thanks for your advice


  • Bob Bona_4
    Bob Bona_4 Member Posts: 2,083
    edited November 2015
    You must use the 5/16 tubing with the CP. Durock with the impregnated styro pebbles is a better choice than the all-aggregate Hardi. Or whichever product has the Styro :) That's an excellent overlayment for your thinset. Be careful screwing it down ;)

    Use the leveler only if you need floor correction.

    You'll get better transfer with the CP than bare tube stapled. Try to get insulated underneath.
  • bmwpowere36m3
    bmwpowere36m3 Member Posts: 512
    I'd use hardi on the floor, thin-set it, screw every 8". The smaller the tube (pex), the shorter your loops have to be... and they minimize floor height transitions.
  • Gordy
    Gordy Member Posts: 9,514
    Use 1/2" plywood sleepers, 6" -8" on center 3/8" pex and 1/4" hard Backer.use heat transfer plates if this is your sole source of heat.
    If you are already married to the climate panels then use hardi backer.
    Speaking of which is this for floor warming, or heating. If the later you need to do a heatloss to determine the load of the rooms.
  • lisi80
    lisi80 Member Posts: 3
    Thanks all for the info
    this will be to heat the 2 rooms it's being installed in.

    Gordy - we are still deciding on how exactly to tackle this. What are sleepers? I can't seem to find much on it.

    Also - another question is whether we should replace our hot water tank with a combi unit to accommodate both the domestic hot water and the radiant. we have a steam boiler now and a hot water tank, we were going to add a small tankless unit just for the radiant.
  • Rich_49
    Rich_49 Member Posts: 2,627
    Making any suggestion on source without knowing the heat loss requirements is a bad idea . Tankless , even the smallest available is probably not a good idea , more than likely be overkill . Possible that a new water heater with a flat plate and 2 small circs would be a better investment . The latter will certainly work and you'll get a new efficient water heater also . Not any water heater will do though .
    You didn't get what you didn't pay for and it will never be what you thought it would .
    Langans Plumbing & Heating LLC
    Serving most of New Jersey, Eastern Pa .
    Consultation, Design & Installation anywhere
    Rich McGrath 732-581-3833
  • Gordy
    Gordy Member Posts: 9,514
    So is there steam rads in the rooms your installing the radiant in? Is it your intent to get rid of the steam all together?

    You can run a hot water loop off of a steam boiler.

  • lisi80
    lisi80 Member Posts: 3
    we removed the steam rads in the kitchen and bathroom where we are doing the renovating.

    we considered running a loop off the bottom of steam boiler into a heat exchanger but it seems like a lot more work then replacing the hot water tank with a combi unit
  • Gordy
    Gordy Member Posts: 9,514
    Well at any rate you need to do a heatloss for those 2 rooms to decide on tube density, water temp, and flow rates. Like Rich said a tankless is overkill.

    Kitchens, and baths can be difficult if the floor area does not allow enough emitter. Example kitchens have cabinets, and islands. Baths possibly have tubs, showers, and vanities.