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Karin
Installing wall thermostat for baseboard heater

Hi,

I'm installing new double pole thermostats for my baseboard heaters and am stumped on how to wire them properly. The two thermostats I've removed so far have either been wired wrong or single pole.

It looks to me like I have an extra set of wires and I'm not sure how to work them in. In the electrical box, I have a total of three groups of wires:

  • upper left hand - both white and black are hot
  • upper right hand - neither are hot
  • bottom - out to heater

All of the diagrams I've been able to find, have just one incoming set of wires and one outgoing set, so I'm not sure what to do with the extra ones. They were used in the previous wiring scheme.

It's about 10 degrees out, so I'm hesitant to take another thermostat apart until I get things sorted out.

Thanks in advance for any suggestions.

Karin

Re: Installing wall thermostat for baseboard heater

Karin could the extra "dead" set be the feed to another heater? You could verify this by checking across the wires with an ohmeter or continuity checker. If they show continuity, turn off the heater and see if the reading shows "open".

The white lead that is "hot" should be identified with a piece of black tape.

Good Luck from Columbiana, Alabama
Maurice Turgeon,http://thesemi-retiredelectrician.com

canuk
Re: Installing wall thermostat for baseboard heater
Karin wrote:

Hi,

I'm installing new double pole thermostats for my baseboard heaters and am stumped on how to wire them properly. The two thermostats I've removed so far have either been wired wrong or single pole.

It looks to me like I have an extra set of wires and I'm not sure how to work them in. In the electrical box, I have a total of three groups of wires:

  • upper left hand - both white and black are hot
  • upper right hand - neither are hot
  • bottom - out to heater

All of the diagrams I've been able to find, have just one incoming set of wires and one outgoing set, so I'm not sure what to do with the extra ones. They were used in the previous wiring scheme.

It's about 10 degrees out, so I'm hesitant to take another thermostat apart until I get things sorted out.

Thanks in advance for any suggestions.

Karin

How was the orginal thermostat wired ?

More than likely you are working with a 220/240 volt system
and explains why both a white and black wire are both live ( hot ).

Typically with a double pole ---both the white & black hots would join to one set of connections ( top or bottom ) of the thermostat and the outgoing lines ( to the heater ) would connect to the other set on the thermostat.
Is there another heater run that's also controlled the thermostat ? --- that would explain the other wires you mentioned at the junction box.

If so then all 4 outgoing lines ( to the heater ) would be joined together and connected at the outgoing side on the thermostat.

Karin
Re: Installing wall thermostat for baseboard heater

Thanks for the ideas. I'll do some more investigating.

In the meantime, it's the two bedrooms where I've taken the thermostats off and they each have just one heater. I've got other rooms (living and dining/kitchen) that have multiple heaters on one thermostat. Haven't ventured to those yet.

Also, I've gone back to the picture of the single pole thermostat that I took before disassembling. All three white wires are bundled together, the two incoming black wires are pigtailed to the thermostat. The wire to the heater is also attached to the thermostat.

JLMCDANIEL
Re: Installing wall thermostat for baseboard heater

How do you know that the white and black of the upper left are both hot? It sounds like you have 120 volt heater with an out going feed to something else. If that is the case you can use the double pole by pig tailing to the white to one input screw and the pigtail form the blacks to the other and both heater wires to the output of the thermostat.

Jack

Fencepost
Re: Installing wall thermostat for baseboard heater

Is the circuit breaker for the heater twice as thick as breakers for your lights & outlets? If so, it's most likely a 240V heater. Double-check the nomenclature plate on the heater (may need to pop the cover off) to make sure it's not 120V. Some will list both 208V and 240V.

If that's the case, then the previous installer simply put in a single-pole thermostat on a 240V heater; this is a common thing to do but not a very good idea as the other "hot" wire (in this case the white) is not switched. That means that the heater remains energized even when off.

If you can confirm that it is 240V, based on your description of what you had with the single pole t-stat, wire up one "half" of the t-stat just like it was before ("line" side to the two blacks; "load" side to the heater). Wire up the other "half" to the white wires exactly like you did with the black wires.

NOTE: do not put two wires under a single screw head; you will not get a good connection. Instead, use a wire nut to create a "pigtail" and wrap the single pigtail wire under the screw.

Can you give us the brand & model of your new thermostats? We can look up the installation instructions and that will allow us to give better advice.

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