3

I'm trying to install a new thermostat that needs a C wire hookup. There are currently 4 wires running from the thermostat to the furnace, none of them are a c wire. When I look at my furnace itself it has a spot to put a c wire but it's currently being used by my whole-home humidifier.

If I run a separate 18-1 wire from my thermostat to the furnace can I just wire both the humidifier and thermostat to the one c-wire hookup?

2 Answers 2

5

I also have a thermostat that requires a C wire hookup for wifi access. The spec calls for a 24 volt DC and I presently have it wired to share a 24 volt termination on my AC air handler. What I discovered was that this termination in the air handler does not provide a constant output of 24 volts. Instead, it cycles as called upon by the air handler and the thermostat would run until the battery failed which took about a month. Plus I could not get the wifi to properly pair with the thermostat due to the cycling of voltage on and off to my C wire termination at the thermostat.

This afternoon I have an electrician coming to give me a dedicated wire from a 24 volt transformer for my C terminal. I expect this to solve my problem.

So based on my experience, be cautious of sharing unless you know the source will provide constant power.

1
  • This is exactly what we found. The C-Wire would only turn on with the furnace was running. We bought a 24vac transformer and hooked up that to the c-wire slot and an r-wire slot and it worked great!
    – Paul Lemke
    Nov 6, 2011 at 20:02
1

You can have multiple devices utilizing the C terminal at your furnace.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

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