How to Install a Honeywell Thermostat (Every Model)

A Honeywell thermostat installation is a low-voltage wire swap: you turn off the power, label the wires on your old thermostat, connect each one to the matching terminal on the new wall plate and finish setup on the thermostat or in the app. Almost every current Honeywell Home model uses the same wall plate, so the steps barely change from one model to the next. What does change is how the thermostat gets its power and how you set it up, so this guide covers how to install Honeywell thermostat models step by step, then the details that differ.

If you’re still choosing one, our guide to the best Honeywell thermostats compares the current lineup.

The quick version

Here’s the whole job, start to finish:

1. Find your model and check that your system is compatible.
2. Turn off the power at the breaker and check the system won’t turn on.
3. Take a photo of the old wiring and label each wire by its terminal letter.
4. Remove the old thermostat and wall plate.
5. Level the new wall plate, drill the holes and fit the anchors.
6. Set the R-switch, connect each wire to its matching terminal and screw the plate to the wall.
7. Attach the thermostat and turn the power back on.
8. Finish setup, then test heating, cooling and the fan.

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Before you start

Find your model. On most Honeywell thermostats, the model number is on the back of the faceplate, and it starts with letters like TH, T, RTH or RCHT. It’s also on the box. The model tells you which wall plate you have and whether you need a C wire (a common wire that gives the thermostat constant 24 V power):

Model	Wall plate	Power	Setup
X2S, X7S, X7B, X8S	UWP	C wire required	Resideo Connect app or on the thermostat
X2P	UWP	2 AA batteries, always	On the thermostat
T5, T5+, T6 Pro Smart, T9, T10	UWP	C wire required	Resideo Connect app or on the thermostat
T4 Pro, T6 Pro	UWP	2 AA batteries, C wire optional	On the thermostat
RTH2300, RTH221	Flat wallplate, screw terminals	Batteries, C wire not used	On the thermostat
Wi-Fi 9000 (RTH9585WF) and other older Wi-Fi models	Flat wallplate with an R-Rc jumper	C wire required	On the thermostat, then the app

The UWP (Universal Wall Plate) is the square plate with push-in terminals and a small door that comes with every current model. Honeywell says C wires are required on all its Wi-Fi thermostats, so if you’re installing a smart model, check for a C wire first.

Check that it will work. Honeywell’s thermostats work with most 24 V heating and cooling systems, including heat pumps. Take the cover off your old thermostat and look for these signs that your system isn’t compatible:

• Thick black wires joined with wire nuts, or an old thermostat labeled 120 V or higher. That’s a line-voltage system, usually electric baseboard heat.
• Terminals labeled A, B, C or 1, 2, 3, which means a communicating system.
• Wires on G1, G2 and G3 terminals (a multi-speed fan). Honeywell says none of its retail thermostats support this.
• A millivolt system, usually a wall or floor heater. The basic RTH2300 and RTH221 do work with millivolt systems; the smart models don’t.

Gather your tools. You’ll need a Phillips screwdriver, a small flat screwdriver, a pencil and a level, plus your phone to photograph the wiring. A drill helps too: Honeywell lists a 3/16 inch bit for the X-series plates, while T-series boxes include red anchors (drill 7/32 inch holes) or yellow anchors (3/16 inch). A wire stripper and needle-nose pliers can help with short or bent wires.

Know when to call a pro. Stop and call a professional if you have a dual fuel system (a heat pump with a gas or oil furnace), wires labeled V and VR, two separate C wires, or a heat pump with Y1, W1 and W2 wires. Honeywell’s manuals send all of these to a contractor or to support. If you’d rather not do it at all, our guide to smart thermostat installation cost covers what pros charge.

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How to install a Honeywell thermostat, step by step

These steps follow Honeywell’s installation guides for the X-series and T-series models, which all use the UWP. Older models with a flat wallplate follow the same order, with the differences covered further down. For the same job on other brands, see our guide on how to install a smart thermostat, or our guide to ecobee thermostat installation for an ecobee.

1. Turn off the power and check it’s off

Turn off the breaker (or switch) for your heating and cooling system. Some systems have separate breakers for heating and cooling. To check, set your old thermostat a few degrees above room temperature in heat mode, or below it in cool mode. If nothing turns on within 5 minutes, the power is off. If your old thermostat is digital and its display has gone blank, you can skip the check.

2. Photograph and label the wires

Take the old thermostat off its wall plate (most pull straight off; some have a screw or a clasp) but leave the wires connected. Take a clear photo that shows the letter next to each terminal. Then:

• Write down which terminals have a wire and the color of each one.
• Put a label from the box on each wire as you disconnect it, using the terminal letter, not the color. Honeywell says there’s no color standard.
• Ignore jumpers (a short wire or metal staple between two terminals, often R and Rc). The UWP doesn’t need them.
• Leave any wire that wasn’t connected to a terminal unconnected.

3. Remove the old thermostat

Release the wires from the old wall plate and unscrew it. Wrap the wires around a pencil so they can’t fall back into the wall. If your old thermostat has a sealed glass tube of mercury inside, don’t put it in the trash: contact your local waste authority about recycling it.

4. Mount the wall plate

Open the UWP’s door and pull the wires through the hole in the back, with at least 1/4 inch of bare wire showing on each one. Hold the plate on the wall, level it and mark the screw holes. Drill the holes and tap the anchors in until they’re flush with the wall. Don’t screw the plate down yet: it’s easier to connect the wires first. If the new thermostat won’t cover marks or holes from the old one, Honeywell sells optional cover plates.

5. Set the R-switch and connect the wires

The UWP has a built-in R-switch (Honeywell also calls it the R slider tab) that does the job of the old jumper:

• One R wire (labeled R, Rh or Rc): set the switch up and put the wire in R.
• Two R wires (R or Rh, plus Rc): set the switch down, put Rc in Rc, and put R or Rh in R.

Then press each terminal tab, push the wire into the inner hole and let go: the tab stays down. Put one wire in each terminal, matching the labels, and gently tug each wire to check it’s held. Compare the result with your photo, push the extra wire back into the wall, then screw the plate to the wall with all three screws and close the door.

6. Attach the thermostat and turn the power on

On the X2P, T4 Pro and T6 Pro, put two AA batteries in the back of the thermostat first. (The T6 Pro Smart runs on the C wire instead, and the T6 Pro Z-Wave takes three AA batteries; our Honeywell T6 Pro review explains how each model is powered.) Line the thermostat up with the wall plate and press until it snaps into place. Then turn the breaker back on.

7. Finish setup and test it

On the X-series and T5/T6 Smart models, the screen asks whether you want to set up with the app or on the thermostat. With the app, you use Resideo Connect (the app formerly called First Alert), which finds the thermostat and walks you through the rest. Either way, you answer a few questions about your system, such as whether it’s a furnace, a boiler or a heat pump, then connect to Wi-Fi. Our guide on how to connect a Honeywell thermostat to Wi-Fi covers each model’s Wi-Fi steps. Finally, run the heat, the cooling and the fan for a few minutes each.

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Honeywell thermostat wiring: what goes where

Most installs are a straight letter-to-letter match: W to W, Y to Y, G to G, C to C. These are the wires that confuse people:

• R and Rh together. On the X-series, if your old thermostat had an R wire and an Rh wire, set the R-switch down, put the R wire in Rc and the Rh wire in R.
• C wire. On the battery models, connect a C wire if you have one: it’s optional on the T4 Pro and T6 Pro and powers the backlight on the T4 Pro. The X2P runs on its batteries either way.
• Heat pumps. Don’t use the W terminal. Auxiliary heat goes to AUX, and on the X2P, X7 and X8S an E (emergency heat) wire goes to AUX too. During setup you choose whether the O/B wire runs the reversing valve in cooling (O) or heating (B): if you’re not sure, trace the wire to the equipment or ask a pro. Our guide to aux heat explains the heat pump terms.
• Separate O and B wires. Some older heat pumps have both, and the B wire is often a common. Honeywell’s instructions differ by model here, so follow your model’s guide, and call a pro if another wire is already in C.
• S, U and L/A. These are for wired sensors, humidifiers or ventilators, and heat pump fault alerts. Not every model has them (the X2S and T5 have no S or U terminals), so check the new model’s terminals before you start if your old thermostat used one.

Honeywell’s own thermostat wiring guide lists every terminal, and our thermostat wiring diagram shows common systems.

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If you don’t have a C wire

Every Honeywell Wi-Fi thermostat needs a C wire, and many older battery thermostats didn’t use one. You have three options:

• Use a spare wire. Look where the wires come out of the cable sheath: some homes have an unused wire tucked back. Connect it to C at the thermostat and to C on the furnace or air handler’s control board, then close the furnace cover fully (some systems won’t run with it open).
• Use the Honeywell C-Wire Adapter. It installs at the furnace and turns your G and Y wires into C and K, so you need both a G and a Y wire, and it doesn’t work with heat-only systems. Your new thermostat needs a K terminal. The X8S box includes a voucher for a free adapter.
• Call a pro to run a new cable.

If you only have two wires for a heat-only system, a battery model like the X2P or T4 Pro avoids the problem, and our guide to 2-wire thermostats covers the smart options. Our C-wire adapter guide compares the adapters.

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Older Honeywell models

RTH2300 and RTH221. These basic programmable models use a flat wallplate with screw terminals. Label the wires while they’re still on the old wallplate, then loosen each terminal screw, insert the wire and tighten it. Keep the jumper between R and Rc unless you have both an R and an Rc wire. They don’t use a C wire: wrap the end of a C, C1 or X wire with electrical tape so it can’t touch anything. They also don’t work with heat pumps that have aux heat, or with two-stage systems.

Wi-Fi 9000 (RTH9585WF) and other older Wi-Fi models. The wallplate has a jumper loop between R and Rc: remove it only if you have both an R and an Rc wire. These models need a C wire and won’t turn on without one. Once it’s on, you connect it to Wi-Fi from its own screen (Menu, then WiFi Setup on the 9000), then register it on Total Connect Comfort.

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If it doesn’t work after installing

Most problems after a Honeywell thermostat installation are power or wiring problems:

• The screen stays blank. Check that the breaker is fully on, the furnace cover is closed and the C wire is connected at both ends. On a battery model, check the batteries.
• The system doesn’t start right away. “Wait” or a flashing Cool On or Heat On means the thermostat is protecting the compressor, which can take up to 5 minutes.
• The system does the wrong thing. Compare the wiring with your photo, check the R-switch position, and check the system type and O/B setting.

Our guide to Honeywell thermostat problems covers each fix, and our guide on how to reset a Honeywell thermostat helps when you need to start setup over.

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The bottom line

For most homes, a Honeywell thermostat installation takes the same seven steps on every current model: power off at the breaker, photograph and label the wires, mount the UWP, set the R-switch, connect each wire to its matching terminal, snap on the thermostat and finish setup. Check for a C wire before you start if you’re installing a Wi-Fi model, and call a pro for line-voltage, communicating or dual fuel systems.