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I’m using Honeywell WiFi enabled thermostats to control heating and cooling at home and cottage. I would like to add another thermostat of the same type simply so that I can remotely read the temperature in the basement of the cottage, not to control the furnace. Should I be able to simply attach ground and C wires to that 2nd thermostat?

Thx ... Dave.

  • What model is your thermostat? Many of the fancier Honeywells can use a remote temp sensor accessory.... – ThreePhaseEel Nov 3 '19 at 21:25
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    "ground" and "C" are the same wire ... – brhans Nov 3 '19 at 23:04
  • There are WiFi thermostats like the Ecobee and Nest that support remote temperature sensors. I have an Ecobee with a remote sensor in each bedroom and it works great. The sensors last a year using a coin-cell battery. – JPhi1618 Nov 4 '19 at 16:02
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No, the stat needs 24vac for the wifi, which is supplied by the furnace from the R and C terminals. You can easily find on Amazon or other retail sites a "24vac C wire adapter" and you can install the thermostat anywhere near a 120v receptacle.

  • Thermostats are 2xRTH6580WF and one RTH9585WF in one house (three separate units) and RTH6580WF at the cottage. It's at the cottage that I want to be able to read the basement temperature when we're away. I hadn't used my meter on the wires and assumed that C was power, since there was a ground as well (I think). So I could simply use a 24vac transformer and not attach to the furnace at all ? That would be a better solution and ensure that no one could screw around with the settings on that basement thermostat to conflict with the other. – Dave. Nov 4 '19 at 11:34
  • Interesting. Yes, I disconnected all wires other than the C & R from an existing thermostat and read the voltage - 27 - and plugged in the thermostat and sure enough it was then operating as a wifi remote sensor. I guess that I'll go ahead and purchase the other thermostat to install at the cottage when we're up there at Christmas. Thanks for the assist. Dave. – Dave. Nov 4 '19 at 13:29

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