Existing thermostat is a Honeywell and has a separate connections for Aux (white wire) and E (Emergency black wire) The proposed Honeywell T'stat only has a single terminal labeled "Aux E".

How do I connect this?

Choices are several:

  1. Secure the Black wire and connect the white wire only?

  2. Secure the white wire and connect the black wire only?

  3. connect both wires parallel at the Aux E terminal?

  • A picture of any diagrams would be helpful. – JACK Jun 14 at 23:45
  • What model is your new thermostat? Can you post photos of the wiring at the air-handler/furnace for your system? – ThreePhaseEel Jun 15 at 0:02
  • 1
    Don't treat this lightly. Emergency heat is serious business. It typically costs 4 times as much to run it. The thermostat should be programmed to only use e-heat when primary heat is absolutely unavailable e.g. due to low temperatures. If you play casual with the connections here, you could find your electric bill jumping $300 in the winter. – Harper - Reinstate Monica Jun 15 at 4:45

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