Replacing 2-wire with five wire on my furnace

[mrjohneel]

I have a two-wire line running from my 1-stage furnace with no cooling to my thermostat. I am upgrading my thermostat and it needs a C wire. Now, I know there are various ways of hooking up adapters, etc., to compensate for the missing C wire. I could even get another type of thermostat. But because it is a short run from my first floor thermostat to my furnace, I want to replace the old wiring with new wiring. So I am going to get an 18/5 wire. My furnace wiring diagram shows R to R, G to G, W to W and B/C to B/C. That's four wires. What do I do with the other one -- the yellow one? Do I hook it up Y to Y even though I don't have a compressor/air conditioning system? Is there anything I'm forgetting? Thanks in advance.

 

[semipro]

I have a two-wire line running from my 1-stage furnace with no cooling to my thermostat. I am upgrading my thermostat and it needs a C wire. Now, I know there are various ways of hooking up adapters, etc., to compensate for the missing C wire. I could even get another type of thermostat. But because it is a short run from my first floor thermostat to my furnace, I want to replace the old wiring with new wiring. So I am going to get an 18/5 wire. My furnace wiring diagram shows R to R, G to G, W to W and B/C to B/C. That's four wires. What do I do with the other one -- the yellow one? Do I hook it up Y to Y even though I don't have a compressor/air conditioning system? Is there anything I'm forgetting? Thanks in advance.

Leave the Y unhooked at the furnace end and connect it at the thermostat end. That way if someone installs an AC or heat pump in the future they won't have to worry about the Y connection at the thermostat. They may otherwise assume (wrongly) that it is connected.

 

[yooperdave]

Leave the Y unhooked at the furnace end and connect it at the thermostat end. That way if someone installs an AC or heat pump in the future they won't have to worry about the Y connection at the thermostat. They may otherwise assume (wrongly) that it is connected.

But, I would like to add to make sure the Y conductor (that is unattached at the furnace) does not come into contact with any metal. A small wire nut on the end would be best.

Once someone looks at a T-stat and notices the AC capability, the possibility of (unknowingly) energizing that Y circuit increases and if the end of the Y conductor is in contact with metal.....