Need slab temp sensor for radiant?

Terry

I've seen short lengths of pex used as the "thermowell", this way the sensor can be removed & replaced as required.

Terry

Dylan Thomas

or is it unneccessary?

I've got a friend of mine remodelling a basement. He's working with an engineer (please keep the groans to a minimum) to work up a radiant heat system for the new slab that will be poured in the next few weeks.

The plan, as far as I've discerned, is to lay 2" beadboard insulation on top of the graded soil, then wire mesh reinforcement, followed by PEX tubing. Slab will then be poured on top of this setup.

I've two concerns- one, no gravel under the insulation. This is a walk-out basement on a fairly steep hill, probably not the worst drainage scenario, and maybe a question for a different set of experts.

The radiant question is about 'slab temp sensors' Is this neccessary? I've seen them installed as an electrical apprentice, and can understand why one may want to know if the slab is too hot, too cold, or ramping slowly or quickly to temp.

If this would only benefit certain systems, or be critical for all radiant systems, I'd like to know before they pour the slab- I may install some conduit as insurance. Any hints on where to locate a sensor of this type in the slab would be welcome.

Thanks for any input-
-Dylan

Terry

depends....

I usually use a T'stat or RTU IF THERE WILL BE NO CONFLICT with other sources of heat. i.e. If you use only a T'stat and it's located close to Aunt Bessies Space Heater (or fancoil supplied area), it will not put heat in slab leaving the slab outside this area to cool down.

A slab sensor can be used to maintain a slab/surface temp without being overriden by other source.

hope this helped & didn't confuse....

Terry @ Frontier.

Dylan Thomas

Thanks much-

Terry, that was exactly the sort of info I was looking for, thanks. This zone should have no other heat sources in it, with the possible exception of sunlight coming through the sliders. That shouldn't prove to be a problem, though. It sounds like the slab sensor won't be needed here.

I'd still be curious to know the best way of roughing in a sensor before pouring the floor, just in case it ever comes up.

Thanks again-
-Dylan

bob carey -midland,mich.

vaper barrier

I would reccomend a vaper barrier under the stryofoam. bob

Dylan Thomas

Thanks everybody!

I met up with the homeowner today and he and I kicked all the suggestions around-

I doubt we'll do a slab temp sensor, but we might rough it in as mentioned in Terry's post.

The vapor barrier is something I forgot about, I'm sure we'll talk about that some more. Gravel looks moot as he's had a drain system installed around the entire exterior of the footings.

Thanks to all-

Dylan

Paul_6

excellent on the

perimiter drainage, water traveling under the slab will increase your heat loss by about 40%. Paul

Dana Zaichkin_7

slab sensor

Here's a rough-in I did prior to suspended slab. I may never use a slab sensor in this install, but it sure is easier to put it in now! I used 1/2 nonmetalic conduit, slightly reamed the bend and slipped in the copper stub with a little cement.

Best Regards

DZ

kevin

ditto!

on the vapor barrier! a rel good thing to have....how much is a rool of heavy mill plastic...kpc