Brand New Nest Power Connector - C-Wire Substitute for Home System Without C Wire - Compatible with Nest thermostats C-wire substitute for Nest thermostats: nest thermostats are designed to work without a C wire in most homes, but for some systems, including heating-only, cooling-only, zone-controlled, and heat pump systems, you'll need a nest power connector or C wire Works with 24 VAC systems: nest power connector is only compatible with 24 VAC systems, so it won't work with millivolt or high voltage systems Installation is simple: attaches to your furnace, air handler, or zone controller, and comes with simple instructions