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airheatman, HVAC Technician
Category: HVAC
Satisfied Customers: 8369
Experience:  Furnace, A/C and heat pump specialist.
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I am trying to install wifi thermostat and do not know what

Customer Question

I am trying to install wifi thermostat and do not know what the x2 circuit does on this old Honeywell thermostat
JA: I'll do all I can to help. Tell me a bit more about what's going on so we can help you best.
Customer: i have a Honeywell rth9580wf i am trying to install
JA: Is there anything else important you think the HVAC Technician should know?
Customer: old thermostat is a xt500c, all the wiring matches up except for 2
JA: OK. Got it. I'm sending you to a secure page on JustAnswer so you can place the $5 fully-refundable deposit now. While you're filling out that form, I'll tell the HVAC Technician about your situation and then connect you two.
Submitted: 1 year ago.
Category: HVAC
Expert:  airheatman replied 1 year ago.

X2 is emergency heat on old thermostat.It will go to the W2/AUX/E terminal along with your white wire .The 9580 uses one terminal for both emergency and auxiliary heat.This just energizes backup heat in both modes.