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
  • 1
    "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

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

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.