I’m in the process of replacing a Braeburn 1200 thermostat with a Honeywell Pro 4000, pn# TH4221D, in that I have a 2-heat / 1 cooling Heat Pump system. The 2nd heating system is a natural gas furnace, which I typically run throughout the colder months by placing the existing thermostat in the ‘Emergency’ position.

In general the electrical connections are straight forward (one-to-one) with regard to most all of the pins (R, O, B [blank], C, Y, E, & G). The question / concern I have has to do with the White wire; connected to the W2 terminal (2nd Stage Aux Heating) on the Braeburn thermostat, leaving either the ‘L’ or the ‘AUX’ connection on the Honeywell unit?

According to the Honeywell Installation Guide, the ‘L’ connection “Sends an output when set to Emergency Heat”, where as the ‘AUX’ connection is for the “Aux Heat Relay”. My guess is that the ‘L’ connection is a continuous output, and the ‘AUX’ output is only available when the thermostat is requesting a heat cycle. However, I’m not completely sure of my interpretation of the brief notes in the Installation Guide, or which connection the 2nd heating system requires? In advance “Thank you” for your response.