How do you install heating thermostat only for furnace?

Answer 1

I am assuming that by asking about a "heating thermostat" for a "furnace" we are not talking about air conditioning/heating units or about electric heating units (baseboard, wall-mounted, etc.).

If the furnace already has a thermostat installed then it is just a matter of replacing the existing thermostat with a new one. Heat-only thermostats can be obtained from home centers such as Lowes or Home Depot. They should be specified to work on 24-volt circuits, unlike those designed for 110/220 volt AC electric heaters. Replacement is simply a matter of removing the thermostat cover, detatching it from the wall, and disconnecting the two wires from the old unit. Connect the wires to the new thermostat and mount it to the wall in place of the old one. Be aware that some thermostats must be adjusted level to work properly - read the enclosed literature that comes with the new unit.

If this is a new or replacement furnace that has never had a thermostat connected then there are several additional considerations. You will need to identify a location for the thermostat. This location should be on an interior wall, out of any drafts, and in a location such as a hallway which is an "average" of surrounding rooms. You will have to run 2-conductor thermostat wire (available at home centers) from the furnace to the thermostat. Connections to the thermostat are as outlined above. The connections at the furnace end depend on the type of furnace - passive hot air, forced hot air, passive hot water, circulator-driven hot water, steam, etc. These variations are beyond the scope of this general question.