Can I use a wifi thermostat with this furnace ? I don't see a terminal c to hook up wire to power up thermostat.. furnace is a GMPN condensing gas furnace .

Are you sure there isn't a c terminal on the control board where the rest of the t-stat wires hook? Do you have central a/c? If so, where do the two wires that go to the outside unit hook to? One should go to y on the control board, and the other to c. Can you post a pic of your control board?