Honeywell Thermostat Wiring For Heat Pumps

Ready to take charge of your home’s comfort? Look no further! Our ultimate guide to Honeywell thermostat wiring is here to empower you. Say goodbye to confusion and hello to seamless installation or replacement. From single-stage simplicity to multi-stage mastery, we’ve got you covered.

Before we go into the actual wiring tutorials let’s look at the honeywell thermostat wiring code just to familiarize yourself with the wire colors and the function.

Honeywell thermostat wiring color code

Wire Color	Terminal	Function
Red	R/Rh/Rc	Power (24VAC)
Blue	C	Common (24VAC)
White	W/W1	Heat relay (Stage 1)
Brown	W2	Heat relay (stage 2)
Green	G	Fan relay
Yellow	Y/Y1	Compressor contactor (Stage 1)
Light blue/ others	Y2	Compressor contactor (Stage 2)
Orange	O/O/B	Reversing valve (Cooling/Heat pump)
Brown	E/Aux/W2	Emergency heat
Not fixed	L/A	Heat Pump fault input
Not fixed	K	Honeywell saver module
Not fixed	S	Outdoor temperature sensor
Not fixed	U	Unused

Preparing your thermostat for wiring

Here are some notes on preparing your thermostat for wiring:

1. Turn Off Power: Ensure that the power to your heating and cooling system is turned off. This can usually be done by switching off the circuit breaker that controls the HVAC system. It is crucial to prevent any electrical accidents during the wiring process.

2. Remove Old Thermostat: Carefully remove the old thermostat from the wall. Take note of the wires connected to each terminal and their corresponding labels.

3. Take a Photo: Before disconnecting any wires, take a clear photo of the wiring configuration. This will serve as a reference during the installation of the Nest thermostat.

4. Label Existing Wires: If you are replacing an existing thermostat, label each wire according to its terminal designation. This will help you match the wires correctly to the corresponding terminals on your new thermostat.

Things your need to be aware of before replacing your old thermostat with a new honeywell

If your system is a heat only system, ensure to buy a thermostat that supports that type. There are also some thermostats that support only heat pumps.
For example, you may only have 3 wires on your thermostat. Usually thermostats that support heat pumps only will not have the W terminal for heat.

Honeywell 1st Stage Heat Pump System with 1 Compressor (6 Wire)

With a first stage heat pump system you will typically have 6 wires. These wires will include the Fan relay for controlling the fan, the O/B reverse valve responsible for switching between the heat and cool mode.

However, with a single stage heat pump system you should only have 1 Y wire for the compressor relay. This wire is responsible for energizing the compressor.

If your wiring comes with separate R wires( R and Rc) then connect both of them onto the separate thermostat terminals.

However if you only have wire R wire, you are going to connect it to one of the terminals and put a jumper between them.

For Honeywell pro series thermostat thermostats, If there is only one R wire, and it is connected to the R, Rc, or RH terminal, set the slider tap to the up position (1 wire).

But if there is one wire connected to the R terminal and one wire connected to the Rc terminal, set the slider to the down position (2 wires)

Wire	Function
R	Power
Rc	R+Rc joined by Jumper or Slider Tab
Y	Compressor contactor
C	24VAC common
0/B	Changeover valve
G	Fan relay
W	Not needed in heat pump system

Honeywell 1st Stage Heat Pump With Auxiliary/ Emergency Heat (7 wire)

This is also known as a 7 wire honeywell thermostat wiring. A first stage heat pump system will have 1 compressor hence only 1 Y wire. This is the wire that controls the first stage compressor relay.

In addition to the OB/ wire and R wires, you will have an Aux/E wire. The difference between the Aux and the E is that E can only be turned on manually while auxiliary heat turns on automatically in extreme weather conditions where the heat pump can not heat adequately.

In case you have an L terminal, this is a heat pump fault input wire and is responsible for the indicator lights on your thermostat.

For example when your system is using auxiliary or Emergency heat, you will see a light indicator.

You may also see indicator lights when there are other problems with your heat pump system. The L wire is one responsible for controlling those indicator lights.

Wire	Function
R	Power
Rc	[R+Rc joined by Slider Tab]
Y	Compressor contactor
C	24VAC common
O/B	Changeover valveG Fan relay
Aux/E	Auxiliary heat/ Emergency heat relay
L	Heat pump fault input
W	Do not use this terminal for heat pump applications!

2 Stage Heat Pump System With Two Compressors (8 Wire)

(Applies to TH6320U model only)

If you have a two stage heat pump system without secondary heating such as a furnace or auxiliary heating, you will have two Y wires that need to be connected. One wire is for the compressor contactor stage 1 while the other for the compressor contactor stage 2.

Wire	Function
R	Power
Rc	[R+Rc joined by Slider Tab]
Y	Compressor contactor (stage 1)
C	24VAC common
O/B	Changeover valve
G	Fan relay
Y2	Compressor contactor (stage 2)
L	Heat pump fault input
W	Do not use this terminal for heat pump applications

2 Stage heat pump system with Auxiliary heat/ Emergency Heat Pump System (10 Wire)

For a heat pump with 2 stage heating with 2 compressors and secondary heating

You expect to have to Y1 (compressor relay stage 1) and (Y2 compressor relay stage 2)

In addition to this, you will need to have the AUX/ W1 connected. This wire controls the heat steps or secondary heat. See how the wiring should be done in the chart below:

Wire	Function
R	Power
Rc	[R+Rc joined by Slider Tab]
Y	Compressor contactor (stage 1)
C	24VAC common
O/B	Changeover valve
G	Fan relay
Aux/E	Auxiliary heat /heat relay
Y2	Compressor contactor (stage 2)
L	Heat pump fault input
W	Do not use this terminal for heat pump applications!

Dual Fuel System (TH6320U / TH6220U only)

Wire	Function
R	R Power
Rc	Rc [R+Rc joined by Slider Tab]
Y	Y Compressor contactor (stage 1)
C	C 24VAC common
O/B	O/B Changeover valveG Fan relay
Aux	Auxiliary heat
E	Emergency heat relay
Y2	Compressor contactor (stage 2 – if needed)
L	Heat pump fault input
S	S Outdoor sensor
W	W Do not use this terminal for heat pump applications!

Honeywell Thermostat Wiring For Conventional Systems (forced air and hydronics)

Conventional Heat And Air Conditioner with Single Transformer (6 Wire)

A typical 5 wire honeywell thermostat wiring for a furnace and air conditioner will have Y wire( for the air conditioner compressor) and the W for the primary heat relay). The other wires you expected are listed in the chart below.

Wire	Function
R	R Power
Rc	Rc [R+Rc joined by Slider Tab] [2]
Y	Y Compressor contactor
C	C 24VAC common
W	W Heat relay
G	G Fan relay

Heat-only System ( 3 Wire)

For a radiant heating system only, there are 3 wires basically as shown in the chart below.

Wire	Function
R	Power
C	C 24VAC common
W	W Heat relay

Radiant Heat-only System: Series 20 (4 wire)

Remember to set the system type to radiant heat.

Wire	Function
R	Series 20 valve terminal “R”
Y	Series 20 valve terminal “W”
C	24VAC common
W	Series 20 valve terminal “B”

Honeywell Radiant Heat-only System: Power open zone valve (3 wire)

You wont need the Rc ( power for cooling). If you are using a honeywell pro series thermostat, move the slider tab to the top position R ( setting).

Wire	Function
R	Power
W	Valve
C	24VAC common

Furnace with 1st Stage Air Conditioner (5 wire)

Wire	Function
R	Power (heating transformer)
Y	Compressor contactor
C	24VAC common
W	Heat relay
G	Fan relay

Heat-only System with Fan (4 wire)

A Heat only system or furnace with fan fan, you shall typically have 4 wires namely R, C, W G

Wire	Function
R	Power
C	24VAC common
W	Heat relay
G	Fan relay

Honeywell Cool-only System: Air Conditioner (5 wire)

Wiring an air conditioner is a pretty straightforward process . It should typically have red (R), yellow (Y), green (G), and sometimes blue (C). Connect the red wire to the R terminal on the thermostat for power.

Connect the yellow wire to the Y terminal for cooling control. Connect the green wire to the G terminal for fan operation. If available, connect the blue wire to the C terminal for a common connection.

Wire	Function
R	Power
Rc	[R+Rc joined by Slider Tab]
Y	Compressor contactor
C	24VAC common
G	Fan relay

2 stage furnace with 2 stage air conditioner (1 transformer)

To wire a Honeywell thermostat for an air conditioner,

Connect the red wire (R) to the R terminal for power
The yellow wire (Y) to the Y terminal for cooling control,
The green wire (G) to the G terminal for fan operation, and
The blue wire (C) to the C terminal for a common connection.

Connect the white wire (W) to the W terminal for the first stage of heating, the second white wire (W2) to the W2 terminal for the second stage of heating, and the second yellow wire (Y2) to the Y2 terminal for the second stage of cooling. Always consult the specific thermostat’s manual for accurate wiring instructions.

Wire	Function
R	Power
Rc	[R+Rc joined by Slider Tab]
Y	Compressor contactor (stage 1)
C	Common
W	Relay (stage 1)
G	Relay
W2	Heat relay (stage 2)
Y2	Compressor contactor (stage 2)

What is the K wire on a honeywell thermostat?

The K is a combination of the Y and the G wire wire and is to be connected to the C terminal of thermostats that require the C wire. It is a honeywell module saver which you can form if your system does not provide the C wire but your thermostat requires one.

Final thoughts

In conclusion, we hope that our comprehensive guide to Honeywell thermostat wiring for heat pumps has provided you with the necessary information and step-by-step instructions to successfully install your thermostat.

By understanding the wiring principles, preparing your thermostat, and following the correct connections, you are now empowered to take control of your home’s comfort.

We would also like to encourage you to refer back to this guide whenever you need assistance or clarification during the installation process.

If you have questions pertaining to your specific model please write your question in the comment section or send us a message through the email address provided on our website..