I have a Lennox furnace (4 years old) with a programmable thermostat. I would like to hook up the fan so that it can run independently of the heating system. I have 2 wires coming out of my wall Black which is hooked up to RH on the thermostat and white which is hooked up to W, with a jumper from RH to RC. I have traced the wires back to the furnace and found the wiring harness coming from the furnace which consisted of 4 wires red, black, green and blue. Red was spliced into the Black wire from the thermostat (RH) and the black spliced into the white (W). The blue and green wires were stowed and not connected to anything. I understand that the green wire will run my fan, so if I could run a wire of the proper size up to my thermostat and connect it to "G", would my fan run when I select Fan on or would I have to hook up the Blue as well? Also Is there a possibility to put the switch at the furnace if I can't run the wires up to the thermostat?

If you run another wire and hook it to g it will bring on the fan , if you can't do this then by connecting a switch at the furnace and energising" g" from red it will also work.