Ecobee EMS Si Manual page 23

Boiler
R
C
W
EMS Si Thermostat
R2-
* Remove RH/RC factory jumper
C terminal to be connected to heating
transformer common
18
W2
R2+ R1- R1+ Y2 C RH
AUX
Air Handler
Y1
Y2
R
C
G
W
RC G Y N/C
O/B
Single stage boiler with air handler, dual stage cool
2-stage AC
Y1
Y2
R
C