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

https://inkmeridianx.com/s/CWz_TrP_HHfsBLGG0hY9Q

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.