Slab sensor retrofit

John Abbott

I need to retrofit a slab sensor in an existing radiant slab.My thought is to epoxy the sensor into a groove cut into the floor.My question is do I neeed to add anything to the epoxy to help conduct heat or is there a product available that to accomplish my goal?The slab is a 2" overpour on insulation and the sensors purpose is to maintain minimum slab during the heating season.

John

hr

Consider

installing a pice of copper tubing as a "well" this allows you to remove and replace the sensor if, or when it fails. Find a copper tube size that fit the sensor closly, and you could use some heat transfer grease in the well for best conduction. I like to use a chunk of transfer plate to mount the well and give a good "reading" area.

U fin works best, but C works also.

You can flatten a piece of copper tube and solder up a plate type sensor well also.

The tekmar/ Wirsbo sensors fit best in 3/8" copper tube. they seem to be the skinyest of the sensors I have come across. No sharp bends in your condiut to the well however!
Try a dry run before you pour it all in

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John Abbott

Hot Rod......

I am not familiar with the "U" and "C" terminolgy and are you installing the groove in the floor or on it and are you gluing the plate to the floor or just fastening it down.The sensor is a Wirsbo by the way and should I insulate above the plate or no?

Thanks

hr

Depends on

what you will be putting over the sensor. pouring a thin slab? Or just thinsetting onto the exixiting slab? For the ladder, just groove your sensor and plate intoa groove cut into the concrete slab. then I put one or two plastic drill anchors to hold it all until the thinset and tile, or whatever.

I run a piece of pex to a junction box or right to the t-stat location to insert the sensor.

I just happen to have short pieces of aluminum transfer plate lying around. Really all I try to do is get a bigger sensor area by using the plates, and the copper or pex condiut give me a way to remove the sensor later.

I'm not sure why the manufactures say to just pour or thinset the sensors in the floor? Probably because they won't get the call to replace one. Seems like a silly way to install them. I've had sensors fail right out of the box. Wouldn't that be a drag to install a new floor and sensor and have it never work Ought to at least throw an ohm meter on the sensor to check it's reading.

Here is my top to bottom method. Use a pex stub out copper ell or straight, embed it in the floor, however. Then run the pex up to a j box in the wall. Some inspectors may want to see approved electrical condiut.

Then I keep sacraficing my fish tape to fasten the sensor to, shove it down to the end, thermal grease in the copper end. then cut the fish tape with enough in the J box to pull it out later. you really need the fish tape to assure you get it pushed to the end of the copper stub. You can only push a wire so far, without a fish tape. all this easily fits into a 1/2 pex.

Probably use a copper or brass cap and a pex crimp adapter on the botton end, if you don't have a pex stub out. Any conductor is better than just pex for quick and accurate readings.

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hr

More detail

I use the aluminum transfer plates just because I have scraps and samples around. Any conductor on the sensor well will work. Heck a 1/2" copper cap soldered on a cop-pex adapter would work, anything to help the sensor get a quick and accurate reading. No insulation above it.

I run pex from the sensor well right up to a j box location for the wall stat mounting.

Then I install the sensor to a piece of fish tape to shove it all the way in to the sensor well. Cut the fish tape off leaving enough in the j box to remove it later.

Some inspectors may want to see you use electrical condiut instead of pex, I suppose, with the proper box connector

Only problem is that tekmar/ Wirsbo stat does not cover a regular 2X4 electrical box. You need to buy their adapter plate, and they are mighty proud of that chunck of plastic, $$ wise And it looks like an after thought.

Not sure why the Euro designs insist on that 2X2 stat size, very un-American, and just jams all the connections into a tight, hard to wire format, besides not covering an old stat mounting location. But is is the nicest control out there for slab radiant, IMO.

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John Abbott

I guess I didn't.......

explain my problem well or perhaps I'm missing something.The radiant overpour is in place and cured and I have to retrofit a sensor on or in it in some way.


John

hr

Oh

here is another idea, plan B. That tekmar 079 sensor will slide into 3/8" OD copper tubing, but not with a tight bend. Heat shrink the sensor onto a piece of tie wire. This allows you to install and remove the sensor.

Now you need to notch the 3/8 tubing into the slab. Will the slab be covered with tile or wood or something? If so this will work.

If the slab is the finished surface we need plan C.

I use a diamond wheel in my small angle grinder to notch concrete. How close to a wall can you position the sensor? How deep are the tubes in the slab?

Grind a small groove to silicone in the copper tube and sensor.

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John Abbott

You certainly........

have an answer for everything.The tubes are about 1 1/4" down and I have an area under the stairs that I can do anything I like without any concern for asthetics.Thank you so much for your help.

John

hr

glad we got on

the same page. I miss the phone conversations sometimes. Much easier to get a clear picture with voice communication.

There is ALWAYS a way to get where you need to go hydronically speaking. That's a nice control you selected, great for bathroom floors once the owners get past the learning curve on it's operation. Take some time to make sure they understand the workings.

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