It looks like you're new here. If you want to get involved, click one of these buttons!
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?