Plumbing, Electrical, & HVAC

Honeywell Thermostat Wiring Instructions

If in the market for a new Honeywell thermostat, make sure you understand your Honeywell thermostat wiring needs before upgrading.

Q: I installed my new programmable thermostat, but it won’t turn on.

A: If you plan to upgrade to a new thermostat make sure you have the proper number of wires available, otherwise your new thermostat won’t work. If you do need additional wires, you will want to consider how difficult installing new wires will be for your application.

Modern electronic thermostats are no different from any other technology, in that they can do more, but can also seem complicated to install and understand. One comfort to know is the basic wiring hasn’t changed much, with exception of an additional wire to get some programmable digital thermostats operating.

Note: For specific thermostat model installation manuals and wiring instructions, refer to our Thermostat Buying Guide for a complete list and link of manufacturers. Individual thermostat model information is most likely the best place to find particular manuals, and not a general manuals category that can be found within the search function.

SEE ALSO: In-Depth Thermostat Wiring Explained
SEE ALSO: Heat Pump Thermostat Wiring
SEE ALSO: Manufacturer Thermostat Installation Manuals – manuals online or manualslib

4 Wire Honeywell Thermostat Wiring

  • G – Fan (green wire)
  • R – 24 VAC / Rc and R or Rh (red wire)
  • Y – Compressor / air conditioner (yellow wire)
  • W – Heat (white wire)

Note: A previous installer may have used a different set of color wires. This will be a non issue to keep track of if a whole new set of thermostat wires is pulled. Otherwise tag the wires before removing from the existing thermostat, or take note of the terminals each wire is attached to.



5 Wire Honeywell Thermostat Wiring

Some programmable thermostats (e.g. Honeywell Prestige wiring requirements) need a minimum of 5 wires, and maybe more depending on what features you want to operate (humidifier, etc). The additional 5th wire will be for common (neutral), which acts the same as it does on an electrical light switch to complete a path and provide power for the display, closing switching relays, etc.

  • G – Fan (green wire)
  • R – 24 VAC / R and Rc (red wire)
  • C – 24 VAC Common (color can vary per manufacturer – may be blue, purple, brown. etc.)
  • Y – Compressor / air conditioner (yellow wire)
  • W – Heat (white wire)



Furnace Electrical Board Connections

Going into your furnace may sound intimidating, but if you have the basic knowledge of wiring, and know how to remove the proper furnace panels to access the electronics, then you should be fine. The COM 24V terminal will be connected to the C (24 VAC common) of the thermostat.


How to Install Thermostat Wire

If you have easy access to the existing thermostat wires, just remove and follow the same path with the new set of wires. You can use cable ties, electrical tape, or staples (securing wires and cables article). Be sure to take a very conservative measurement on how long your new set of wires should be. You don’t want to start over, if you come up short. Any home improvement store should carry thermostat wiring. Also check local electrical and lighting supply houses.

If wires pass through a floor and up into a wall cavity before reaching a thermostat. Try the following.

  • Start at the thermostat location. (i) A simple trick for pulling new wires to replace existing ones: tape one end of the new wires to the end of the existing wires coming through the electrical box or wall opening. Make sure to tape completely over the wire ends, so no edges are present that can snag something. (image below)
  • Slowly pull the new set of the wires down through the wall from the basement. (i) Use any object larger than the hole in the wall, and tie or fasten to the end of your new wires, so you don’t pull all the wire through the wall. e.g. pencil or flat washer, to act as a stop. Use electrical tape to secure if necessary.

In a situation where the original thermostat wires may have been stapled to an interior wall stud, and not run through conduit, you may be better off leaving the existing set of wires, and cutting them off at the entry and exit points of the wall. Then feed new wires with a fish tape (Klein Tools). Check your local home improvement stores, or local tool rental, for rental availability.

CAUTION: ELECTRICAL HAZARD – Always turn power off before performing any work. Contact a certified HVAC tech if you don’t feel 100% sure of your DIY capabilities.



  1. 1

    I’m going from an old honeywell analog thermostat to a new digital programmable one. My unit is a heat pump. I have figured out what all but a few wires are going to. The ones im most concerned about are W1 and W2. The connections I have on the new terminal are K,L,Aux/E, G, O/B, C, Y, R, RC. I know W2 is supposed to be my 2nd stage heating and should goto Aux, but where should I put W1? Does it goto the Aux terminal as well? Wouldn’t that cause Emergency heat to run all the time?

    Also on my current thermostat the Yellow and Green wires are both on the G Terminal. Shouldn’t the compressor be on Y terminal?

    The connections for my current (old) thermostat are :
    Terminal/Wire Color
    X-Blue (Common on the unit)
    L- No wire
    W2- White
    R- Red
    G- Green and Yellow
    O- Orange
    Y-No wire
    W1- Brown
    E- No wire
    B- No wire

    Thanks for any help

    • 2

      Hi Charles,
      Giving exact advice over the internet about a subject that involves so many different devices is difficult. From my experience, thermostat installation instructions provide both furnace and heat pump wiring guidance. If you are in need of installation instructions for your heat pump as well, try these two sites (manualsonline or manualslib). Together, you should be able to sync the two.

  2. 3

    I’m interested in buy the Honeywell RET97E5D1005/U Wi-Fi Programmable Thermostat and I’m trying to figure out if I have a C wire. I’ve done a lot of research but I can’t seem to find the answer in my particular situation so I’m going to do my best to explain it.

    In my thermostat I currently have wire connected to G, Y, W, and RH. And I also have a jumper going from RH to C (this is the part that’s throwing me off). I have a volt meter and I tested the voltage on all the connections. While touching the RH/C connection and any other connection I got around 28 volts with the air system running and not running. If I tried any other connection that didn’t included RH/C then I would not get any volts while the system wasn’t running.

    In my indoor ac unit my wires that run to my thermostat are labeled C (runs to RH/C), Y (which runs to Y), W1 (which actually runs to G), and a no labeled wire that runs to W. I can’t be certain but it seems that the labeling might be incorrect and that it’s actually suppose to output as R, C, G, and W, but I’m going to continue to refer to the wires as I stated them originally. I traced the C wire back into the unit and discover that it comes directly from the transformer right after it is transformer from 220v. Furthermore if I follow the C wire the other direction (towards the thermostat) then it runs down below the air filter and connects at the frame of the unit to a device that is wrapped in tin foil. The wire runs into the device and then come right back out and runs to the thermostat and is plugged into the RH/C connection.

    That Is all the information I have gathered. I am determined to figure this out and would love some guidence that anyone could offer me.



    • 4

      Hi Logan,
      You started off stating that you have a 4-wire setup (G,Y,W, and RH). With this I am going to say you need to run an new set of 5-wire so you have the common needed for your new thermostat.

      Did you click over to the link In-Depth Thermostat Wiring Explained. I believe the information will fill in the gaps of knowledge you’re looking for.

      Your second paragraph mentions an indoor AC unit. Is this running on the same thermostat or separate?

  3. 5

    I’m replacing a Honeywell T8000C. When I was labelling the wires, the White wire was wrapped around both Y and W screws. I have a heat pump and would like to know where this White wire should go in my new thermostat which is Honeywell RTH6400D. Thanks for any help you can offer.

    • 6

      Hi Shannon,
      I’m going to refer you to this article since you have a heat pump. I believe you’ll find clarity in how a heat pump works compared to a furnace and air conditioner, along with the wiring differences.

  4. 7

    i have a red, Green, Black, yellow and orange wire I see where the red green and yellow go I am confused about the black and orange can you help?

    • 8

      Hi Shannon,
      My initial advice is what has been given in previous replies. See what electrical board terminals the wires connect to on your heating device.

  5. 9

    I’m trying to replace an older Honeywell heat pump thermostat T874R1137 with a newer Honeywell WiFi TH9320WFV6007. The old has a ‘W’ white wire that the new one doesn’t, and the new one requires a ‘C’ wire not on the old one. Also, the old one has separate O and B wires yet the new one seems to combine these. How do I wire this? Honeywell’s web site doesn’t provide the manual for the older model.

    • 10

      Hi Glen,
      See if Manuals Online has your old thermostat manual. Beyond that I always suggest to remove the blind guessing game equation from the process and locate the electrical board of the heating device you’re wanting to control and see which wires are connected to what terminals. Keep in mind a thermostat is just a controller that is sending low voltage(24v or less) signals. Ultimately the thermostat terminals need to be linked to the corresponding heating / cooling device terminals.

  6. 11

    We are replacing an old 4 wire thermostat with a new Honeywell 6580 5 wire. There were two wires pushed back into the wall. We made sure that all the wires match what is in our AC/Heat electrical box and the same wire match on the new thermostat. Our furnace panel is back on with the green light showing lit up, but still now power in the new thermostat? I’m assuming something to do with the C wire not having the current but no idea why?

    • 12

      Hi Amanda,
      Most troubleshooting requires a hands on approach. There are several tests to perform that can’t be done over the phone or online. I would start by checking your furnace installation manual – check manualsonline if you don’t have a current manual – then recheck the wiring to the thermostat again. If all checks out I would then grab my low voltage detector and make sure I’m getting current. Unfortunately this may not be a common tool.

      The wires in the wall may match something you see in your furnace electrical panel, but that doesn’t mean they link together. There are only so many combinations of wire colors and they may be leading to something else. Maybe there was another heat source (e.g. electric baseboard heater) at some point. So the 2 wires you found tucked away may now lead to a dead end, a new 4 wire set was installed going to your existing furnace which does not include a 5th wire for common (24C). Hope this makes sense?

  7. 13

    we are trying to replace a two wire thermostat for steam base board heat with a honeywell rth221b. we have connected it several ways and still not working, did i buy wrong replacement thermostat?

    • 14

      Hi Christy,
      Looking at the RTH221 Installation instructions, one of the designations states “a hot water system (steam or gravity) with or without pump — 2 wires”, so this thermostat should be compatible. There is only one way to connect and have the thermostat working properly. Were the original wires marked so you know what they originally connected to, or do you remember? I’ll need a basic starting point. If you only have 2 wires, did you remove the jumper between RH and RC? If so that needs to be put back in?

  8. 15

    I want to replace a four wire thermostat with a five wire wifi thermostat. The fifth wire is the ‘C’, or common wire. Is this wire a ground / neutral wire to complete the power the display? If this is correct, I can connect the other end of ‘C’ to an electrical neutral and the thermostat will work. Right or wrong?

    Thanks very much for any information.


    • 16

      Hi Dave,
      You’re partially correct. But if you are referring to a neutral (commonly white wire) in your high voltage (110-120v) electrical system, that won’t work. The thermostat to furnace electrical panel are only low voltage components (24v or less). Am I understanding and answering your question appropriately?

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