24 V wifi stat for baseboard heaters


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Old 10-12-15, 12:55 PM
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24 V wifi stat for baseboard heaters

I have electric baseboard heaters at our cabin which are controlled by an old style mercury dial thermostat. The heaters are wired to 240 Volts but there's a 24 volt relay which allows to use the low voltage stat. I would like to use the Honeywell rth6580wf stat which requires the "C" wire. It says on the package that this thermostat is not compatible with electric baseboard heat (120 -240 V), however, I figured that since a low voltage mercury stat works now, I may be able to use a "smart" thermostat if I can get around the "C" wire issue and power the unit some other way. I was thinking to buy a 110 to 24 V transformer and simply plug the stat into a wall outlet as a way to power it. Alternately I was wondering if I can get get a different relay that comes with a "C" wire. Thanks in advance !
 
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Old 10-12-15, 02:33 PM
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Welcome to the forums.

The easiest way to solve that problem is to add a control relay/transformer combo. This device has switching contacts for the heater and three terminals including C to run a 24v thermostat.

Aube-RC840T-240-Switching-Electric-Transformer/dp/B0037MXM1C

You could also do the same thing with your current relay and transformer if you can get to the wiring between them.

With either method you'll still need a third wire for C from the controls to the stat.
 
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Old 10-20-15, 06:09 PM
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If your low voltage mercury thermostat works now, doesn't that imply there already is a 24V transformer?

There should be two wires going into the mercury thermostat. Label one "Rh" and the other "W". Rh is the one that goes to the transformer, and W is the one that goes to the relay. Now find the other output wire of the transformer (same as the other input wire of the relay) and label it C.
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Then remove the old thermostat, and connect the Rh, W, and C to the new thermostat.
Somebody please double check me.
 
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Old 10-20-15, 06:20 PM
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Without seeing the OP's wiring.... it's pretty hard to assign colors. Your diagram is correct but we don't know if the colors used are as you show.
 
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Old 11-30-15, 07:50 PM
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Thanks PJMax, I bought the Aube relay and installed it. Had a lot of fun running a 4 wire cable to it, but got it done. It works great now. Much appreciate the Advice!!
Krys.
 
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Old 11-30-15, 08:25 PM
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Awesome part ! Great job. Thanks for letting me know how you made out.
 
 

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