A wiring configuration tool may be configured to determine a new wiring configuration for a replacement HVAC controller based, at least in part, on the existing wiring configuration for a current HVAC controller and, for example, the make and model of the replacement HVAC controller. The wiring configuration tool may be hosted by a server that provides a user interface for interacting with the user. The user may access the wiring configuration tool via a web services interface, a smart phone application or in any other suitable manner.