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Hydronic radiant floor DIY using cement boards.

majka Member Posts: 3
edited September 2017 in Radiant Heating
We are planing to install hydronic radiant in our house that has concrete slab. The house was built in 50 and it original had radiant floor, however it is impossible to recover that system. We want to use 1/2 PEX tubing but we are very limited with height. We can't go higher than 3/4 of an inch. It would be convenient (and expensive) to use wooden panels designed for that. However, as far as I know the thinnest for 1/2" tubing is 1". Other thing is that it won't transfer the heat in between the tubing and if we use heat transfer plates it would add additional cost. My idea is to either have tubing mounted to concrete slab and then pouring it over with self leveling concrete and here is my first question: How thin it can be? Would 3/4" would be enough to prevent significant cracking? Other option is using cement boards cutting them to fit in between the tubing and gluing them with contractor adhesive to our slab - similarly to the attached photo where they use playwood. Would it work and last? Did anyone tried that? The reason why I prefer to use cement boards instead of plywood is that it will transfer more heat. The last question is what can I use as an insulation while considering very thin self leveling cement or cement boards. Any other ideas how to do it are welcome. Just keep in mind that we can make it only 3/4" thick, we are on a tight budget, and we are determined to do it before we move in (because I know it won't be possible while living in the house). The house is about 1600 square feet on concrete slab.


  • Ironman
    Ironman Member Posts: 7,347
    Someone else may be able to suggest something, but I don't know of anything that would fit into your 3/4" criteria. 1/2" pex has a 5/8" OD. 3/8" pex is available, but that only gains another 1/8".

    I can't see cement boards as a practical method that would give good conduction of heat from the tubing.

    Have you considered radiant ceilings?
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • majka
    majka Member Posts: 3
    Previous owner had installed Air heating/cooling system. We want radiant floors because we know how uncomfortably cold wood floor gets during the winter time. Celing system wouldn't solve our problem.
  • Gordy
    Gordy Member Posts: 9,546
    3/4" overpour would crack, and delaminate from the original concrete. Forget that method. Along with no slab insulation.

    Roth panel system is 3/4" thick with plates, and foam insulatiuon. 3/8" pex. However this is the panel only thickness. What is finished floor?

    If you need only 3/4" build up with finish floor your pretty much screwed. As been said look hard at radiant ceilings.
  • Gordy
    Gordy Member Posts: 9,546
    Another thought would be electric radiant. However I would look very carefully at electric rates.

    Is the build up height concern doors, and trim? If so It's really not that big of an obstacle.
  • STEVEusaPA
    STEVEusaPA Member Posts: 6,506
    majka said:

    We want radiant floors because we know how uncomfortably cold wood floor gets during the winter time. Celing system wouldn't solve our problem.

    Sure it would. Doesn't the sun heat up a floor when it shines on it?
    Same principal. Keep in mind it won't warm 'through' an object.
    Best (least) you can probably do on a floor is a total of 1 1/2, but if the slab isn't insulated, any floor install is going to be a waste of money.
    "Tight budget" does not go hand in hand with radiant floors.
  • majka
    majka Member Posts: 3
    edited September 2017
    We will put engineered floor and that is extra on top of 3/4". 3/4 is the total thickness without the floor. I was thinking to put 1/4" insulation (eg.cork, plywood or under the slab insulation) and 5/8"" precut boards in between the tubing.
    Yes, trims and doors are the concern as well as 3 outdoor doors (including deck sliding doors). It is a brick house so moving them up is out of question. Also, the ceilings are quite low so we don't want to make it even lower.
    JUGHNE Member Posts: 11,021
    The key term of DIY in your header indicates that you are a hands on type.
    Have you considered just doing the jack hammer removal of the existing floor? Great amount of sweat equity involved.
    But simply getting the floor properly insulated is a great improvement over heat loss. Then enough tubing installed would heat the area great.
    Just a thought.