Forgot to install pipe for slab sensor

[OptionalStop]

I installed pex in my floor before it was poured for radiant heating but forgot to install a pipe to put my slab sensor in. I already purchased the Tekmar 519 thermostat that includes the sensor. Is there any good way I can install this sensor or will I be OK to just use room temperature control (if the thermostat has it)?

 

[spudley]

OK I'll play...how did you install radiant in a "already poured" floor?

 

[Mancino]

I have the same thermostat...I didn't like how the system ran with the slab sensor. Seemed to short cycle. I just run the room sensor and use the "outdoor sensor" setting on the thermostat and still keep the slab sensor hooked up. Then I still see the floor temperature, but the thermostat only runs off the room sensor.

 

[klassenl]

You drill a small hole in an inconspicuous spot and drop it in. Or cut a groove with a masonry wheel and grout over it.

 

[OptionalStop]

You drill a small hole in an inconspicuous spot and drop it in. Or cut a groove with a masonry wheel and grout over it.

Great idea, thanks.

 

[Jim greengo]

I'd just use the room thermostat myself.

 

[yeldogt]

The need for a slab sensor is really dependent on the space. I have a glass enclosed room w/ thick masonry floor at one of my houses ... if I allow the floor to only work off a room thermostat ..it will shut the floor off midday with sun gain and the floor will not have time to recover and the sun goes down .. the floor will not heat fast enough. I use a floor thermostat to keep a minimum floor temp ... with some trial and error I have figured out what works to keep the floor warm w/o over heating. The key here is the room has additional heat that can be provided -- It has two panel radiators and also ductwork. The panels have room temp control.

The floor sensor is also valuable in a house with two heating systems .... my new build will have both floor heating and duct work. the radiant is only for warm floors and modest heating ... in colder weather the floor heat temp rise will stop and the other will take over. This keeps the floor from having to do all the heating and possibly be too hot.

In a garage -- a slab sensor can be valuable for the same reason. You pick a minimum temp and just allow/ put up with the solar gain .... since a garage is typically lower temps ... this works out.

A slab sensor is really needed when tubing is spaced far apart -- say 12" in a thick slab. It't just not able to react quick enough.

That's why I always tell people to install more pipe. More pipe closer together allows for faster response and lower water temp ... this is more efficient ...especially with condensing boilers. wide space tubing with constant temp changes ..... needs hot water and no condensing. Less comfort and more $$

Find a spot out of the way -- you can use a sheet of foam w/ cavity for the sensor carved out . glue to slab in middle of pipes. Even behind a baseboard -- interior wall -- on floor. insulate with foam. You want to get the top of floor temp away from tubing.

 

[andyvh1959]

When I installed the tubing before my garage slab was poured I failed to consider a temperature sensor in the system. The tubing is a two-zone system, where the two runs go into the slab from the midpoint of the 28' foot side, route back and forth out to each end on 12" spacing, and return to the manifold at the perimeter on the 28' foot of the slab. Aside from chipping out a section of concrete and installing a sensor covered with epoxy concrete, is there a sensor on the end of a long wire that could be fed into one or both return runs? A tee at the tubing where it exists the floor with a sealed fitting around the sensor wire would allow the sensor wire to route up to the boiler.

Now, of course doing it that way would sense the heating fluid more than actually measuring the slab temperature. It would take some time to correlate the fluid temperature to the desired floor temperature, but it would give me a way to monitor and control the floor heat with a thermostat once I determine what fluid temperature gives me the desired comfort.

This sensor is meant to be installed into a groove cut into the slab, actually sensing the concrete temperature:

072 - Tekmar 072 - Slab Sensor (20' wire)

Tekmar 072 - Slab Sensor (20' wire) - <FONT size=3><BR>The tekmar Slab Sensor 072 has a PVC plastic sleeve which is designed for use in soils or concrete. The 072 is supplied with 20ft (6m) of 2 conductor cable. <br><U>Specifications: </U><BR>Literature: D 079<BR>Packaged Weight: 0.37 lb. (170...

www.supplyhouse.com

If something could be added into the tubing itself then I wouldn't have to cut any groove into the new slab. Or, I just don't bother with an in floor sensor and adjust the boiler setting until I get the comfort level I want.

 

[Terry D]

I have done the same thing with a heated floor mat for a bathroom. Your thermostat should have a option to use room temp instead of floor temp. I personally like using the room temp option anyway. It should be no big deal forgetting to put the pipe in.

Edit - I just realized this is a year and a half old thread.

 

[like2wheel]

When I installed the tubing before my garage slab was poured I failed to consider a temperature sensor in the system. The tubing is a two-zone system, where the two runs go into the slab from the midpoint of the 28' foot side, route back and forth out to each end on 12" spacing, and return to the manifold at the perimeter on the 28' foot of the slab. Aside from chipping out a section of concrete and installing a sensor covered with epoxy concrete, is there a sensor on the end of a long wire that could be fed into one or both return runs? A tee at the tubing where it exists the floor with a sealed fitting around the sensor wire would allow the sensor wire to route up to the boiler.



Now, of course doing it that way would sense the heating fluid more than actually measuring the slab temperature. It would take some time to correlate the fluid temperature to the desired floor temperature, but it would give me a way to monitor and control the floor heat with a thermostat once I determine what fluid temperature gives me the desired comfort.



This sensor is meant to be installed into a groove cut into the slab, actually sensing the concrete temperature:

072 - Tekmar 072 - Slab Sensor (20' wire)

Tekmar 072 - Slab Sensor (20' wire) - <FONT size=3><BR>The tekmar Slab Sensor 072 has a PVC plastic sleeve which is designed for use in soils or concrete. The 072 is supplied with 20ft (6m) of 2 conductor cable. <br><U>Specifications: </U><BR>Literature: D 079<BR>Packaged Weight: 0.37 lb. (170...

www.supplyhouse.com

If something could be added into the tubing itself then I wouldn't have to cut any groove into the new slab. Or, I just don't bother with an in floor sensor and adjust the boiler setting until I get the comfort level I want.

Why not just read return temperature the normal way instead of snaking a bulb up the tube & restricting the flow?

 

[andyvh1959]

Yup, got to thinking about it instead of over thinking it. I'll just monitor the temperature and adjust as needed. I also plan to just keep the floor warm enough to be comfortable working on it. I won't need the shop to be 70 degrees when its freezing outside.

 

[yeldogt]

With open walls you can drill a hole in the lower plate and drop the sensor onto the slab floor -- ideally you want a spot in the middle of the tubes and not on an outside wall.

The slab sensor works best where you have lots of heat gain. I use them in any room with lots of glass. With a low mass fast acting system like warmboard ... ODR or room thermostats (wall) may work fine. Often if there is a lot of glass the solar gain in the afternoon may turn off the floor .... if the floor goes off and cools too much .... the room will be cold when the sun goes down and the floor will not heat up fast enough to keep the room at temp.

This problem will grow as the mass of the floor grows -- a slab floor with heavy stone tile needs a floor temp sensor to keep a minimum slab temp regardless of room temp. I will often have a secondary heat source ... or I like to overlay a serpentine loop of Pex into the system. This extra loop of Pex is built into the heat load calculation and only it is controlled by the room (air) thermostat. The Floor thermostat keeps the rest of the system going.

Supplyhouse sells a Honeywell thermostat that I like the best .... comes w/ floor sensor ... around $85