Nest Thermostat Wiring Question (White Wire, W1 vs W2)

[GWilJr]

I just replaced two new simple Honeywell thermostats in our new house with Nest Learning Thermostats.  I took pictures of both Honeywell units which were wired the same.  The white wire for both units were in the W2 slots.  The Nest app guided me to place the white wire for both Nest thermostats into the W1 slot.  I am wondering if that is indeed correct or if I may have answered a question incorrectly during the app’s attempt to guide me through the process.

I have two American Standard all electric heat pump units.  The larger unit is for the downstairs and there is a smaller unit for a bonus room over the garage.  Each unit has a blower unit in the attic.  Everything was manufactured in 2023. 

Here was the wiring configuration found on both Honeywell thermostats (letter desgination and corresponding wire color):

R - red

W2 - white

OB - orange

Y - yellow

G - green

C - blue

My question pertains to the white wire (or the whole wiring scheme).  Why would I have not simply wired the Nest thermostats exactly as I found the Honeywell units?  Why did the Nest app instruct me to place the white wire in the W1 slot vs the W2 AUX slot?  Was the app correct, or did I make a mistake answering a question, or does it matter?  What problems could occur if I placed the white wire incorrectly?

Thank you!

[zoeuvre]

Hi GWilJr, 

Thanks for posting. The Nest app's guidance to place the white wire in the W1 slot instead of the W2/AUX slot is likely based on the specific wiring configuration and compatibility of your heat pump system with the Nest thermostat. In some cases, heat pump systems may have different wiring conventions or compatibility requirements compared to conventional thermostats. The Nest thermostat may have identified that your specific heat pump system requires the white wire to be connected to the W1 terminal instead of the W2/AUX terminal.

By placing the white wire in the W1 slot as instructed by the Nest app, you're following the recommended wiring configuration for your specific heat pump system as determined by Nest's compatibility algorithms. If you were to place the white wire in the W2/AUX slot instead, it may result in incorrect operation of your heat pump system. The W1 terminal is typically used for first-stage heating, while the W2/AUX terminal is used for second-stage heating or auxiliary heating. Misplacing the wire could potentially lead to issues such as insufficient heating or incorrect staging of the heat pump. To ensure proper operation and compatibility, it's generally recommended to follow the wiring instructions provided by the Nest app.

Let us know if that helps.

Best,

Zoe