I need to change the orifice on my coleman furnace. Can you tell me where the orifice is located?

On the back side of the gas valve. Remove the gas valve and you will see the brass orifice. Why are you changing the orifice?

A furnace has many "orifices" aside from the one mygirlsdad77 pointed out. There are multiple orifices that are changed out to convert from NG to LP... what exactly are you trying to accomplish?

Jones is correct. I jumped the gun. I just saw coleman and assumed it was a trailer house furnace :) Most furnaces do indeed have multiple orifices.