I have a programmable thermostat and would like to run the fan only at times to circulate air in my home. I have a gas forced hot air furnace. I have a two wire system and therefore the green wire to connect to the fan control is non existent. How can I create a three wire system? I figure I need to receive the green wire from the furnace fan to the thermostat to have control of the fan only. Can this be done? How much would something like this cost for a professional to correct?

You need to pull a 4 wire thermostat wire to replace the 2 wire you have now sometimes it's easy depends on where the wire is ran if it just to the basement you could do it yourself