I recently had a furnace installed. The salesman said he would have them put in an intake from the outside because there wasn't one. It's an 80% efficient furnace, older home, but the mechanical room is semi enclosed in its own room. When the salesman was selling me the unit, he said 'these older homes like yours breathe good on their own and probably don't need an intake from outside, but we will put one in anyways'. It is on the service order when he sold me the unit, but when they installed the furnace i guess he said it would be too hard to put in. I told him okay and now i am rethinking it and might have him put the intake vent pipe in from outside.