Honeywell T8090A User Manual

1

69-0750—1

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 all heating, cooling or

heating/cooling systems when thermostat is powered by
batteries. If thermostat is not powered by batteries, refer to
Table 1 for thermostat and system compatibility information.

TABLE 1—SYSTEM COMPATIBILITY FOR NON-BATTERY POWERED THERMOSTATS.

Electric (Line Voltage)—Typical baseboard and
radiant

• The R8239D1015 Isolating Relay or R841 Silent

Switching Center must be installed in the thermostat
control circuit.

a,b

Fan Coil Unit

• Compatible. Assure correct subbase identity selected for

fan control.

b

Gas—Direct Spark Ignition (DSI), Intermittent
Pilot (IP), and Standing Pilot (SP)

• Compatible. If not using battery backup, 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 or limit operation.

b

Heat Pump

• Compatible. Assure correct subbase identity is selected

for fan control and changeover control (O terminal for
cool and B terminal for heat).

c

Hot Water Zone

• Honeywell 2-wire valves are compatible.

b

• Some non-Honeywell 2-wire valves will require an

R8239D1015 Isolating Relay in the thermostat control
circuit.

a,b

• Some 3-wire valves will require an R8239A1052

Isolating Relay in the thermostat control circuit.

a,c,b

Oil

• If not using battery backup, 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.

b

Vent Damper

• Honeywell damper motors are compatible.

b

• Some non-Honeywell damper motors will require an

R8239D1015 Isolating Relay in the thermostat control
circuit.

a

 Check control amperage requirement.

c

Warm Air Zone

• Most are compatible.

b

a

If thermostat is not compatible with the system being controlled, the system will not operate. No hazard exists. The thermostat
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.

b

Cut the two black heat anticipator jumper wires before installing the thermostat. See Set Heat Anticipator section.

c

Consult manufacturer for installation requirements.

M3375