Hello All
I am in currently in the design stage for a new house that will have hydronic in slab heating. I have used Rehau to design the system and although they don't mention in slab temp sensors I have decided to at least allow provision for them to be added later on if need be. In other literature Rehau recommend the use of Tekmar 073 sensors. I downloaded the installation instructions for the sensor and they recommend installation in either a metal or plastic conduit. The installation image shows the sensor protruding from the end of the conduit.
My questions are;
1) Is it better to use plastic or steel conduit for the sensor?
2) Can or should the conduit be capped to prevent concrete entering it during the concrete pour?
3) If the sensors are installed at a later date do they need to be touching the concrete or will it be sufficient to be installed at the end of the conduit if the conduit is capped?

Thanks in advance

Phil

If you are using pex than I don't see a need for one. Room thermostats will make the call for heat and turn the system on.

Most manifolds that you use have inlet and outlet temp needle type indicators on them (though you need to make sure they are accurate - 1/3rd of my 14 are off a couple decrees).

These temp indicators are right in the water flow and tell a better picture of what is going on in the loop. You slab temp sensor is only going to read that one spot. I hand help IR temp gun will work better later, but a Flir IR camera works wonders around the house. For $200 it is worth the investment.

Good Luck

Yes, a thermostat with both indoor air and slab temperature feedback and a heat source that uses outdoor air temperature feedback (i.e., Outdoor Reset) can significantly improve HR controllability. We commonly use the Uponor Setpoint 501S ($176), Tekmar 519 ($83), Tekmar 521 ($121) and Tekmar 552 ($170) thermostats and they all work very well (prices from SupplyHouse.com, our affliate). We use the same 1/2” PEX tube that we use for the circuits to create the slab temperature sensor conduit. We use a ProPex end cap fitting on the end of the PEX tube that is embedded in the slab and a 90 degree elbow on other end that brings the conduit out of the slab into the wall space. The end of the slab temperature sensor conduit should be placed between the PEX circuit tube so as to detect the nominal slab temperature and NOT be in close proximity to the PEX circuit tube where it would be subject to heating cycle temperature gradients. Photo attached.

We use slab sensor a lot in our system design. Tekmar 519 non programmable is $98.00, Tekmar 521 programmable is $136.00. The Tekmar 561 wi fi unit is $189. + sensor.
Best to use pex pipe scrap for sensor well, if possible locate access point of well below the thermostat on the wall location, services by a 2x4 covered plug access at same height of the electrical plugs for a uniform look in the house. The point of this is that if you ever have a sensor failure it will be easily located under the thermostat.
That said if using in a shop or warehouse the sensors can be up to 500 feet from the thermostat, so the thermostat can be set to slab only and monitor slab temp from the boiler room.
This function is great in a truck shop agricultural shop where you are trying to simply maintain a dry comfortable work or storage area.
Slab sensors have the added benefit of setting the minimum slab setting, eliminating a hard cold start to bring heat up in slab.
Dan