Replacing an old Honeywell thermostat usually involves changing to a newer model or to an energy-efficient programmable digital thermostat. This process is straightforward and can be performed using a few simple hand tools.
The first step is to turn off power to the HVAC by switching off the appropriate circuit breaker in the circuit panel. Newer HVAC systems have a standard power switch placed next to them.
Next, carefully pull off the old thermostat cover to expose the thermostat, the connecting wires and the wall plate. Unfasten the screws to detach the thermostat, and then undo the screws holding the wires in position. Note the color of each wire and the specific terminal it is attached to before disconnecting.
Remove the old wall plate by unfastening the attaching screws, and then fix in place the new plate. Strip the cover off the wires by 1/4 inch to expose the copper cord, and attach them to the corresponding terminals on the new thermostat. Then, fasten the new thermostat to the wall plate by pushing it gently until it snaps in place.
Finally, turn the HVAC power back on, and use the instruction manual to program the thermostat to your desired settings. Make sure the old Honeywell thermostat is properly disposed as it may contain mercury.