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GabrielB 12-21-2009 11:09 PM

One thermostat for two baseboard heaters wired this way
Hi guys,

I have been upgrading my thermostats here in the house and I have a little challenge now.

Two baseboard heaters that I assume are wired parallel (you will be able to confirm) had their own unit mounted thermostat. I'd like to upgrade as well but for those two I'd like to use the same thermostat to control them. (same room)

Those 240V baseboards are wired to a 15A breaker with #14 wires.

I've included pictures from the two heaters. Heater 2 is fed from heater 1 to its left side. All wires on heater 1 are located on its right side. Heater 1 is fed to its right side from a third baseboard in another room.

I'm not sure how to connect eveything so the thermostat will control both of them correctly. (thermostat is rated with more than enough watts for the two baseboards.)

I have found similar questions here and there but it didn't adress the specific wiring questions I have here.

Thanks for your help!

Heater 1

Heater 2

Diagram (very rough sketch that I did for myself at first - hope it will do. W=white. B=Black)
Left part is heater 1. Right part is heater 2.

hayewe farm 12-21-2009 11:34 PM

1 Attachment(s)
In your diagram the thermostat on the left is switching the white leg and on the right the thermostat is switching the black leg. You will need to do a little rewiring so the single thermostat switches the same leg on both.

AllanJ 12-22-2009 07:22 AM

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GabrielB 12-22-2009 11:57 AM

Thanks for the quick answer and diagram hayewe!
Very much appreciated.

All right this did work but I'm just wondering if those two heaters are wired in serial now? Wiring things like batteries in parallel or serial is easy to grasp but I never fully understood what makes baseboard heaters connected in serial or parallel.

I'd very much like to understand this before putting everything back together and fixing the baseboards on the wall.


hayewe farm 12-23-2009 08:40 PM

In my diagram they are wired in parallel, the power white lead goes to both loads and the power black lead goes through the thermostat to both loads. The thermostat itself is in series with both loads. If in series the white power wire would go to the first unit and the other wire from the first unit would go to the second unit and the other wire from the second unit would go to the thermostat and the other side of the thermostat to the power black wire.

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