Brown wire for intertherm heating thermastat

Need to see where the brown is hooked at the funace, this will tell what its function is therefore telling you what terminal it needs to hook to at the thermostat. Its possible its not even used. Most common collors on a conventional heat system are red white yellow green, sometimes you will see blue black brown orange etc. The main thing is that you know what color wire is hooked to what terminals on the furnace. Then hook them corrospondingly to the thermostat. Good luck and hope this helps.