I recently purchased a Bosch 2 stage central a.c. with a heating inverter. I have baseboard heating and but have a large and opened family room so didn't want to run more pipes. The Bosch will work up to 5 degrees but living on long island temps sometimes get colder so I still have to use the baseboard heating. Any recommendations regarding a smart thermostat that will control both heating systems? I have the honeywell 9000 but I funny believe will control both. I appreciate any suggestions.
The W2 (Aux/E) terminal on the thermostat is for a second stage heat relay or heat pump auxiliary / emergency heat.
Note that this is to energize a relay or contactor coil, which will in turn energize your baseboard heaters; you can't directly switch baseboard heat with the Honeywell 9000.
Selecting a contactor or contactors and rewiring your baseboard heat so that it is controlled by the smart thermostat rather than the line voltage thermostats you're using now could be an easy job, could be a hard job, depends on the existing wiring.