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Thread: 240 line voltage thermostat for baseboards seems to be self heating

  1. #11
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    heat at thermostat

    I have installed many digital wall thermostats connected to one or more baseboard heaters. There is one thing I have notice after returning to the job several years later. In many cases where the homeowner burns candles or is a poor housekeeper there is a dark smudge on the wall above the thermostat. This would indicate air rising through or around the thermostat. I assume the heat is rising because the thermostat is a little warmer than the surrounding air?

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    This is why the t-stats on baseboard heaters and some of them on the wall do not have temperature numbers but rather just number settings. You set the T-stats to where it is comfortable.
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    Quote Originally Posted by Dennis Alwon View Post
    This is why the t-stats on baseboard heaters and some of them on the wall do not have temperature numbers but rather just number settings. You set the T-stats to where it is comfortable.
    Most of those are mechanical and don't have internal heating issues of any significance.

    Differences like a draft in the wall will make them appear to be inconsistent from room to room.

    Mounting any thermostat above the baseboard heater it controls will probably eventually heat up the room, but it may short cycle a few times because of being right over the heater. Mounting any thermostat in "line of sight" of a radiant heater will have similar effects.
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    Next steps

    Hi Guys, Thanks for weighing in on this. A couple of details -- The thermostat I am zeroing in on is on an inside well sealed wall about 12 feet away from the 1000w baseboard on the opposite wall. Aube is a very popular manufacturer in Quebec. Every Aube I have seen has that dark streak above the thermostat, candles or no candles -- I do a lot of house inspections. I like the idea of stretching the unit forward into the room air to isolate it from the wires -- will do and report back. I actually have two units fairly close together (was two bedrooms made into one) so I can even do some comparative testing with other brands. Then I will take this entire forum thread and take it to the manufacturer for their response.

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    Aube states in their instructions that the thermostat will be warm. I assume that they have differential circuitry to allow for that but have not measured room temperature independently. I have a digital thermometer I can move about so I will take some measurements and post the results. Right now my Aube in the den is not calling for heat and the Aube is cool to the touch. I will get a comparison here and move to the bathroom where I can easily play with temperatures and get some comparisons there.

  6. #16
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    Quote Originally Posted by Jon E View Post
    Hi Guys, Thanks for weighing in on this. A couple of details -- The thermostat I am zeroing in on is on an inside well sealed wall about 12 feet away from the 1000w baseboard on the opposite wall. Aube is a very popular manufacturer in Quebec. Every Aube I have seen has that dark streak above the thermostat, candles or no candles -- I do a lot of house inspections. I like the idea of stretching the unit forward into the room air to isolate it from the wires -- will do and report back. I actually have two units fairly close together (was two bedrooms made into one) so I can even do some comparative testing with other brands. Then I will take this entire forum thread and take it to the manufacturer for their response.
    In my view Aube/Honeywell stuff is good. I'm not a big fan of line voltage stats, no matter who makes them. When cost is not an issue I think a much better and flexible solution is to use a low volt stat driving a relay. This avoids the inevitable situation down the road when the customer wants to use something like a NEST or such. Aube makes a really good potted heating relay-very quite and durable.

  7. #17
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    Quote Originally Posted by Eddie_T View Post
    Aube states in their instructions that the thermostat will be warm. I assume that they have differential circuitry to allow for that but have not measured room temperature independently. I have a digital thermometer I can move about so I will take some measurements and post the results. Right now my Aube in the den is not calling for heat and the Aube is cool to the touch. I will get a comparison here and move to the bathroom where I can easily play with temperatures and get some comparisons there.
    Interestingly my Radio Shack digital thermometer read a couple of degrees higher than either Aube.

    Using a Taylor precision bulb thermometer in my den w/o demand the Taylor reads a bit over 70° and the Aube reads 72° but the wall may be a bit warmer as there is a PTAC heat pump running on the other side of the wall.

    In the bath the Taylor and the Aube read the same with demand at 74° and w/o demand at 72°.

    In the bath I placed the Taylor bulb on the vent of the Aube and with demand the Taylor read 77
    ° and the Aube 72
    °.

    So in my case even though the Aube is warm to the touch with demand the circuit seems to disregard it.

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    Quote Originally Posted by Jon E View Post
    I am constantly finding 240v line voltage programmable thermostats that are "under heating". Room temperature is quite below the temperature indicated on the thermostat. They appear to be maintaining their setting temperatures, as judged by their own readout, but I finally realized with an infraRed gun that the thermostat box itself was often 10 deg C hotter than the wall adjacent. I further identified that this "heated box" syndrome was hotter when it was controlling more power -- ganged baseboards. I am getting nothing from the manufacturers. This is happening with several models of Aube but I have received complaints of other brands also maintaining room temperature considerably below the set points. Is it possible that the wiring itself inside the box behind the thermostat is heating the thermostat and kicking out before the ambient temperature is reached? When I look behind the problem thermostats there appear to be a pretty tightly packed set of wires.
    I've noticed this too.

    The triac based 'programmable' tstats tend to get hot. Many also have wattage limitations lower than traditional line tstats as well.

    I don't know how much savings are actually seen from the digital ones, but I much prefer the good old contact on and off !

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    I’m not familiar with is Adobe thermostat but one thing comes to mind.........do these thermostats have “anticipators” little thermal elements connected to the thermostat that warm up when the heater is on, with this type line and load connections are important.

  10. #20
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    Quote Originally Posted by mopowr steve View Post
    I’m not familiar with is Adobe thermostat but one thing comes to mind.........do these thermostats have “anticipators” little thermal elements connected to the thermostat that warm up when the heater is on, with this type line and load connections are important.
    I've only seen the anticipator in standard mercury-bulb and bi-metallic-strip T-stats.
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