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Installing a t-stat floor probe in an existing concrete slab?

benjamin_wooten | Posted in General Questions on

Hello friends! Quick question here…

We are working on a remodel in a house with an existing in-floor radiant heating system. However, the house did not have a thermostat with a floor probe installed when the slab was poured.

We pulled up the laminate flooring, and polished the concrete slab, and would like to install a new t-stat with a floor sensor.

I know the preferable installation would be to have run it in a conduit between the pipes *before* the slab was poured, but in this situation – with an existing slab – can we simply drill a hole into the slab and drop the sensor into it, standing on end? Would you affix the probe into the hole with anything (silicone for example), or just leave it loose in there?

Or is there a better approach to take?

Thanks for any advice!

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  1. GBA Editor
    Martin Holladay | | #1

    I've never done this. But at a minimum, you need (a) to determine the location of the Pex tubing embedded in the floor (perhaps with an infrared camera), and (b) drill a hole in a location that is between two parallel runs of tubing rather than right beside a length of tubing.

    My guess is that you will want this location to be in the mechanical room or directly under the bottom plate of a partition (so that you can protect the wire attached to the sensor).

    If I were doing this, I would insert the sensor and then pour some soupy grout (Portland cement, sand, and water) into the hole. But perhaps a GBA reader will suggest a different approach.

  2. benjamin_wooten | | #2

    Thanks very much, Martin. I will likewise wait to see if anybody else chimes in, but it sounds like snaking it through to the mechanical room would work fine, and I can affix it with soupy grout as you suggested.

    I know the sensors aren't supposed to be set "close" to any heat sources, like a refrigerator. I have a very convenient space behind a tall cabinet that sits in the refrigerator alcove, that would preclude me from having to run the wire through another wall to get to the mechanical closet... the sensor would be buried at least 24" away from the fridge. Any idea whether or not that qualifies as far enough away?

    Thanks again!


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