What Is W2 Wire On Thermostat? W2 Wire Thermostat Wiring (2nd Stage)

On many thermostats, you will find a W2 terminal. There is quite a lot of confusion about what is this W2 wire on a thermostat; namely, what is that W2 wire supposed to power. To help everybody out, we are going to explain exactly what the W2 wire thermostat is.

Note: You will connect a wire to the W2 terminal in very limited and specific cases. Typically, you don’t connect to the W2 terminal in 3-wire, 4-wire, 5-wire, or even 6-wire thermostats. The only relevant cases where you would connect a wire to the W2 terminal are 7-wire and 8-wire thermostats.

w2 thermostat wire with a white wire connected to w2
On most thermostats, the W2 terminal is left unconnected. Here is an example of Honeywell 5-wire thermostat; W2 is not connected, the heating unit is run via W1 terminal.

Alright, as you have probably seen in our thermostat wire color codes article here, the W terminals on the thermostat are connected to by white heating wires. All heating wires – the ones that connect to your furnace or heat pump (heating mode) – will have a white thermostat wire.

In standard Honeywell thermostat, we can find three types of these W white wires:

  • W terminal. This is the basic heat terminal. You would connect to it for simple heating devices, such as 1-stage furnaces.
  • W1 terminal. W1 means first-stage heat. You will see a lot of one-stage heat pumps using this terminal. In many cases, the heat pump is connected to W1 and jumped to Y1 (first-stage cooling). That’s because the heat pump can either heat or cool; the orange or dark blue wire connecting to the O/B terminal will switch the reverse valve, effectively switching on heating mode or switching on cooling mode.
  • W2 terminal. W2 means second-stage heat. In general, this is reserved only for 2-stage heat pumps (heating mode); there are quite a few exceptions to this rule, we’ll cover them all.

Basically, the key difference between W1 vs W2 is that W1 is used for standard 1-stage heat pumps while W2 is used for 2-stage heat pumps.

Here are all other instances when we will have to use a W2 terminal and how to wire the W2 terminal:

When Do We Use W2 Terminal On Thermostat?

In general, the W2 terminal is reserved for second-stage heat pump heating. But that’s not it.

This is what the W2 is used quite a lot for:

  • Heat pump with furnace backup. At very low temperatures, the heating mode of a heat pump becomes less efficient (COP can drop below 2.o from 3.5+). That’s when it becomes financially reasonable to start heating with a gas furnace. The W2 terminal can be used to wire this dual setup.
  • Wiring the 1-stage heat strips for a heat pump. This seems a bit paradoxical; the W1 is commonly used for a 1-stage heat pump or a furnace. However, when you don’t have a W terminal on the thermostat (but only W1 and W2), you would in some Honeywell thermostats wire the 1-stage to W2.
    w2 terminal not connected
    Example of a thermostat without W terminal. You only have W1 and W2 terminals.
  • Wiring the 2-stage heat strips for a heat pump. This is only in the case of the straight electric system.

Here is how you can wire the W2 terminal:

W2 Terminal Thermostat Wiring

There are several different ways how to connect the W2 terminal (always use white heating wires). You can:

  • Connect the white wire directly to W2.
  • Connect the white wire to W1 and use a jumper to W2.
  • Connect the yellow wire (cooling wire) to Y2 and use a jumper to W2.
  • (In very limited cases) Connect the E terminal (emergency heat) and use a jumper to W2. This is not exactly how it should be done, but we see many cases with this kind of wiring.

All in all, it is useful to know that, in most cases, the W2 terminal is unused. If you don’t have a 2-stage HVAC heating unit, you don’t really have to worry about it. In some specific cases we listed above, you will see the W2 wired.

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