This is the only doorbell looking transformer that I found in my home. It is right behind the wall that connects to the thermostat “below”. This is inside the garage close to the HVAC.
It does say load 16V 10VA which is what you’d expect from a doorbell transformer. But no idea if it’s solely for the thermostat or is also being shared by the doorbell. It says “Smarthome 1591” in the picture; which on Googling returns results for a doorbell transformer). It's wired right around the HVAC/thermostat so I have no idea if it's a shared one or not.
I attached a Ring doorbell to existing wires and it doesn’t seem to power up. Neither touching the doorbell wires seems to cause the chime to ring. May need to swap out the transformer but not sure it is the right one?
I am planning to install Nest and I may have to replace this one in any case. I just don’t know if I need to find another one for the bell or is it shared? How to be sure?
PS: the existing thermostat is working.