Wiring diagrams: Humidifiers and Dehumidifiers
The 2nd generation Nest LearningThermostat is compatible with most whole home humidifier and
dehumidifier systems that connect to your thermostat with one or two low voltage wires.
Compatible wires have one of the following labels:
•
H, Hum, Hum1, H2, Hum2
•
D, DH, Dhum, Dehum, D2, DH2, Dhum2, Dehum2
Regardless of whether your system has one wire or two, you will need to figure out if the humidifier or
dehumidifier can be activated on its own or if it requires heating or cooling to be activated at the same
time. You’ll also need to determine other settings, such as whether the fan is required during operation.
Nest's * (STAR) terminal is a powered terminal. If connecting to a humidifier/dehumidifier that requires
connection to unpowered terminals, add a 24VAC relay suitable for HVAC equipment use. Consult
humidifier/dehumidifier installation manual for wiring requirements.
Important Note:
In dual transformer set ups (where there is both an Rh and an Rc wire connected to Nest),
Nest will power the * connector from the Rh wire.
Label
Function
Y1
Compressor Relay (Stage 1)
Y2
Compressor Relay (Stage 2)
G
Fan Relay *
O/B
Heat Pump Changeover
Valve
Rc
24VAC power from cooling
transformer
W1
Heat Relay (Stage 1)
W2/AUX
Heat Relay (Stage 2)/
Auxiliary Heat Relay
C
24VAC Common Wire
†
*
Star connector: W3, E, HUM,
or DHUM
Rh
24VAC power from heating
transformer
‡
Nest Learning Thermostat installation & configuration guide
Page 15
