Nest and Ecobee can work with many common 24V heating and cooling systems, including some heat pumps

https://articlegrovey.com/s/6J5aMCYOZb9pMJJ1OurfK

Nest and Ecobee can work with many common 24V heating and cooling systems, including some heat pumps, though certain homes may need a C-wire or add-on power accessory.