Honeywell RTH8580WF User Manual page 17

Installing your thermostat
Note:
The Wi-Fi thermostat requires a C wire to operate. The C, or common,
wire brings 24 VAC power to the thermostat. Many older mechanical or battery
operated thermostats do not require a C wire. If you don't have a C wire, try:
• Looking for an unused wire that is pushed into the wall. Connect that wire
to C and check that it is connected to the 24 VAC common at your heating/
cooling system. Check the video section at wifithermostat.com
• Installing a new wire. If required, contact a contractor to install a new wire
(go to wifithermostat.com to locate a contractor in your area).
Wiring
conventional
For
conditioner), see page 16. See "Glossary" on page 65 for further definition.
heat pump
For a
further definition.
heating/cooling systems (natural gas, oil or electric furnace, air
system, see page 17. See "Glossary" on page 65 for
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