Currently, I have a front doorbell button and a back doorbell button. I have a chimes unit on the first floor and a chimes unit on the second floor. Pressing the front doorbell will cause both chimes to "ding-dong" and pressing the back doorbell will cause the chimes to "ding." This works as expected.

I want to install a chime unit on the third floor.

One concern I have is the doorbell transformer won't be able to drive all three chime units. How do I determine which transformer I need?

I'm also concerned that if I do need to upgrade my transformer the current wiring won't be up to snuff. Given a transformer, how do you determine the appropriate doorbell wire?