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Thread: Thermostat with Remote Bulb Help

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  1. #1

    Default Thermostat with Remote Bulb Help

    Hey guys,

    I'm looking to buy a thermostat with a remote bulb. The bulb needs to embedded in the concrete. The run on the bulb is only about 5'. This will be the thermostat for a boiler system that will serve as a floor warming system.

    The thermostat needs to be at least slightly attractive. Nothing overly fancy but no elongated dial units. Any ideas on where I might find one of these?

    I've checked Graingers and several online sources and I've yet to find anything that fits my description.

    Thanks

    Tom

  2. #2
    In the Trades Bob NH's Avatar
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    I have used the Ranco ETC-111000. It is an electronic control unit and the sensor cable is 8 ft, but you can add many ft of cable to it because the additional resistance doesn't affect the measurement. You can route the sensor and power wires out the back so you don't have ugly wires exposed on the wall.

    If the boiler is using a 24 Volt system you can get the ETC-112000 model from Grainger and use low voltage power for the electronics.

    I would put a tube in the concrete so the probe could be put in after pouring and removed for repair or replacement.

    If you have access to the bottom of the floor you can curve the tube a bit so the open end is exposed and the other end is embedded where you want it in the concrete. The sensor is 1/4" diameter and about 2" song so a 3/8" ID tube will be big enough.

    For heat-transfer reasons you will get the best accuracy if you put the tube in so that maybe 2 ft of tube is embedded in the concrete and located approximately equidistant from any pair of heating elements (wires or tubes).

    If you search on the famous auction site for RANCO ETC-111000 Microprocessor Temperature Control you will find some for sale.
    Last edited by Bob NH; 01-26-2008 at 01:48 PM.

  3. #3

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    Bob,

    Thanks for the reply. I looked that unit up on the famous site and I'm not sure that's what I'm looking for. Let me expain the situation better. The house is a slab house. Exising with radiant floor heating in the slab. What I'm looking to do is mount a thermostat on the wall with a temperature measuring device that runs down the wall and that I can slip right behind a piece of trim. Drill a hole in the concrete and imbed the probe into the slab. Thereby the thermostat will not measure the air temperature but the floor temperature and call for the boiler to cycle when the temperature drops so many degrees.

    Does this description help?

    Thanks

    Tom

  4. #4
    DIY scratch-pad engineer leejosepho's Avatar
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    In this list of various models of thermostats, "A" means air temperature is measured and controlled, "F" means floor temperature is measured and controlled, and "AF" means air temperature is controlled but limited by a maximum floor temperature.

    It sounds to me like you are looking for something like a TH113-F that will read the floor temperature and signal your boiler's 24-volt control circuit when heat is needed. An "AF" model would do essentially the same (as in my own embedded-wire system) by attempting to heat the floor up to an adjustable point no greater than 104* as long as the ambient air temperature is below the demand setting. I do not know the maximum floor temperature for the TH-113.

    http://www.aubetech.com/products/lis...amille=1&app=7

  5. #5
    In the Trades Bob NH's Avatar
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    Quote Originally Posted by statjunk View Post
    What I'm looking to do is mount a thermostat on the wall with a temperature measuring device that runs down the wall and that I can slip right behind a piece of trim. Drill a hole in the concrete and imbed the probe into the slab. Thereby the thermostat will not measure the air temperature but the floor temperature and call for the boiler to cycle when the temperature drops so many degrees.
    The thermostat will measure the temperature of the probe, whether it is in air or concrete. The description of how I would put the probe in a new floor is to minimize any differences between the concrete and the sensor. Where that is not possilbe, one does the best that can be done.

    I would put a little grease in the hole to provide good heat transfer from concrete to probe, and plug the hole at the top to keep junk out.

    The dead band (range betwen on and off) is adjustable, and you will want to keep the setting small because the temperature of the concrete will change slowly.

  6. #6

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    Search Graingers for "line voltage thermostat" and you find what you seek. There are a few with 8' probes.

    I have done several radiant in slab systems, and would never consider reading the slab temp. I use the Honeywell -very simple- line voltage units with dual bulb technology, and control the pump directly for simplicity. I make sure the unit is placed out of drafts and sun and centralized to the home main living area. With a bit of zone tuning, soon you will never touch the unit again except to bump up or down a few degrees.

    If I was in Alaska, I would consider monitoring outside air temp with that probe to get a lead on a cold spell, and to turn the pump on early.

  7. #7

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    Quote Originally Posted by Raucina View Post
    Search Graingers for "line voltage thermostat" and you find what you seek. There are a few with 8' probes.

    I have done several radiant in slab systems, and would never consider reading the slab temp. I use the Honeywell -very simple- line voltage units with dual bulb technology, and control the pump directly for simplicity. I make sure the unit is placed out of drafts and sun and centralized to the home main living area. With a bit of zone tuning, soon you will never touch the unit again except to bump up or down a few degrees.

    If I was in Alaska, I would consider monitoring outside air temp with that probe to get a lead on a cold spell, and to turn the pump on early.
    Raucina,

    Above you say that you would never consider reading the slab temp. Then you go on to say that you line voltage units with dual bulb technology and control the pump directly.

    Isn't that what I'm attempting to do? Just allowing the user to set the temperature and then the pump will turn on when the slab lowers in temperature by so many degrees?

    Tom

    P.S. Thanks to all that have offered input. Greatly appreciated.

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