I want to use this thermostat for a propane furnace. No AC involved. It is a 24 V system with three wires. Green wire goes to G on the existing thermostat terminal block. Gray wire goes to W on block and red wire goes to RH. The thermostat that I am using now works fine however I want to be able to monitor house temps. by Wi-Fi app. Also want to set temps up or down using the app. The Nest thermostat has a built in rechargeable lithium ion battery so will it be charged with my present system? Will a "Nest power Connector" need installed?
If you have a c - wire, you can use that, but if none there's the nest power connector. I believe you have the thermostat with 2 triple A batteries on its back. Usually, it's recommended to have a c - wire or nest power connector installed so that your thermostat will work smoothly for the long run. If you don't have the nest power connector or a c - wire, then Google will send you an email notification that you'll need a nest power connector, or while you're installing the nest thermostat and while setting it up from google home app, the app will recommend the nest power connector.
I just wanted to jump in real fast to see if you saw eveluna's reply and to see if you still needed some help on this or if you were able to get it sorted out. If you are still needing some help, just let us know and we'll be happy to continue helping.
I wanted to follow up and see if you are still in need of any help. Please let me know if you are still having any trouble from here, as I would be happy to take a closer look and assist you further.