2-wire to 5-wire furnace hookup | RIDGID Forum | Plumbing, Woodworking and Power Tools - HVAC Discussion

Sorry if this is an electricians questions rather than an HVAC question: 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 (Gas-Fired, Direct Vent Condensing) 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.