My old thermostat is 24V, but it uses thick threaded wires.-

[lsholguin]

They are thick threaded wires, but I have measured carefully with a multimeter, and I am sure it is a 24 V system.

Can I simply solder them to a 18 to 22 gauge wires so they can fit to the Nest “holes”?

[AxelD]

Hi lsholguin,

Thanks for posting in the Community and for your interest in a Nest Thermostat! If you've already confirmed the voltage is 24V, it might be compatible. However, I recommend contacting a local HVAC technician or Nest Pro to verify your system can be rewired. They're best equipped to assist with hardware configuration.

Regards,
Axel