Trane XL824 E wire

[jakematic]

I'm getting ready to replace an old Honeywell with an XL824 on my heat pump system.




Everything makes sense except there is an E wire on the existing thermostat.
Where does that go on the new one ? Thanks.

[Thermostat]

The E and the Aux most likely do the the same thing on your HVAC system. Typically the Aux (back up heat or electric heat) is enabled when the heat pump can not keep up. The E is enable when you manually command the thermostat to not use the heat pump and use back up or electric heat. On some older indoor units there are separate heating elements for Aux and emergency heat.