User's Manual

Before you go any further, determine

what your existing wiring and equipment

situation is.

A. If you have a Heating only system without Air Conditioning, the First

Alert model sTHERM-500 will require 3 wires: R (24Vac), C (24Vac)

and W (Heat). Most systems that only have Heating use very simple

thermostats that require 2 wires: the R (24Vac) and W (Heat). The

THERM-500 thermostat requires 3 wires to supply power to the

thermostat. In this case an Add-a-Wire accessory will not work and it

will be necessary to install another wire for the C (24Vac) connection.

B. If you have a single stage fossil fuel heater with air conditioning, the

First Alert model THERM-500 will require 5 wires for independent fan

control. They are R (24Vac), C (24Vac), W (Heat), Y (Cooling), and G

(Fan). You may connect only 4 wires, as instructed in the “Making 4

Wires Work When 5 Wires Are Required” section on page 50.

If there are only 4 wires present that are connected to the existing

thermostat, there are at least 3 options available to connect the First

Alert THERM-500:

1. Use the 4 wires as instructed in the“Making 4 Wires Work

When 5 Wires Are Required” section on page 50, and note that

the fan will only operate with a Heating or Cooling demand.

2. Pull new thermostat wire from the HVAC equipment to the

thermostat so that there are at least 5 wires available.

3. Purchase and install an Add-A-Wire accessory.

C. If you have a multi-stage HVAC system comprised of a fossil fuel

heater with air conditioning, the First Alert model THERM-500 will

require the 5 wires mentioned above (R, C, W, Y, G) plus an additional

wire for each additional stage of Heating or Cooling. You may reduce

the 5 wire requirement to 4 if you give up independent fan control

following the instruction in the “Making 4 Wires Work When 5 Wires

Are Required” section on page 50, or use the optional Add-A-Wire

accessory.

Installation Instructions