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it is because you have 2 stages heat.
If you want a single wire...just wire nut a single wire in with the 2 ends. Then attach the single end into thermostat.
The thermostat you had existing nor the ecobee are really exactly what you want for your system...so they combined the 2 stages
yes you can.
The black wire for you is actually electric back up heat. Which usually uses a thermostat with a emergency heat selection..this turns off heat pump and uses electric backup in case of heat pump fail.
when previous thermostat was installed the emergency heat became auxiliary heat (second stage only).
Being a 1986 unit...the efficiency you gain will be minimal.
basically the w1, first stage heat is heat pump...the black wire "emergency" heat was used as a second stage.
This is coming from description...but the only time we see white and black tied together is when a thermostat was installed without emergency heat option.
When you are all set just rate service at top of page and then you have 30 days of follow up available.
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