Heating or Cooling and Heating/Cooling
New Construction Thermostat,
Wallplate and Subbase
Installation Instructions for the Trained Service Technician.
M3375 Recycling Notice
Check thermostat and subbase (if used) suitability for the
heating, cooling, or heating/cooling system. Refer to Table 1.
Assemble tools required: flat bladed screwdriver, hand or
power drill with 3/16-in. drill bit, wire cutter/stripper or
sharp knife, bubble level or plumb bob and line.
Assure power is off to the heating, cooling, or heating/
cooling system at the main fuse panel. Most buildings have
a separate switch box or circuit breaker for disconnecting
power to the heating and cooling (if applicable) equipment.
This thermostat is compatible with most heating, cooling,
or heating/cooling systems. Refer to Table 1 for thermostat
and system compatibility information.
This control contains mercury in a sealed tube. Do not
place control in the trash at the end of its useful life.
If this control is replacing a control that contains mercury
in a sealed tube, do not place your old control in the trash.
Contact your local waste management authority for in-
structions regarding recycling and the proper disposal of this
control, or of an old control containing mercury in a sealed
If you have questions, call Honeywell Inc. at 1-800-
TABLE 1—THERMOSTAT AND SYSTEM COMPATIBILITY.
Type of Heating System
to be Controlled
Electric (Line Voltage)—typical
baseboard and radiant
The R8239D1015 Isolating Relay or R841 Silent Switching Center must be
installed in the thermostat control circuit.
Fan Coil Unit
Compatible. Assure correct subbase identity is selected for fan control.
Gas—Direct Spark Ignition
Compatible. Assure that 24V control transformer common is accessible for
connection to thermostat cable conductor and power to the transformer is not
regularly interrupted by high temperature or limit operation.
DSI), Intermittent Pilot (IP), and
Standing Pilot (SP)
Compatible. Assure correct subbase identity is selected for fan control and
changeover control (O terminal for cool and B terminal for heat). Jumper Y
to W for heat pump compressor control.
Hot Water Zone
Honeywell 2-wire valves are compatible.
Some non-Honeywell 2-wire valves require an R8239D1015 Isolating Relay
in the thermostat control circuit.
Some 3-wire valves require an R8239A1052 Isolating Relay in the
thermostat control circuit.
Assure that the 24V control transformer common is accessible for connection
to thermostat cable conductor and power to the transformer is not regularly
interrupted by high temperature, purge cycle, or limit operation.
Honeywell damper motors are compatible.
Some non-Honeywell damper motors require an R8239D1015 Isolating
Relay in the thermostat control circuit. Check control amperage
Warm Air Zone
Most are compatible.
If thermostat is not compatible with the system being controlled, the system will not operate. No hazard exists. The thermo-
stat will not be damaged unless it is used to directly control a line voltage system. For proper system operation, a Honeywell
R841 or R8239D1015 Isolating Relay must be added to the thermostat control circuit.
Consult manufacturer for installation requirements.
D.F. • Rev. 11-94 • 1 M3375 • ©Honeywell Inc. 1994 • Form Number 66 99 -- 00 55 66 44 —— 33