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Wiring question - R and RC

I'm about to replace my Honeywell thermostat (RTH8500) with an ecobee 3. Today, the Honeywell is connected as follows:

Thermostat Wire Furnace Circuit Board
RC Blue Wire R
R Red Wire R
W White Wire W
Y Yellow Wire Y
G Green Wire G

As well, there is a C (Common) terminal on the furnace circuit board which is not currently connected by wire to the thermostat.

Given the above, can I use the Blue wire as the C-Wire between my ecobee and the furnace or do I need to use the PEK and connect both the Blue and Red wires to the single R/RC/RH terminal in the PEK?



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