Had the heating guy come out a couple of days ago cause me and the wife smelled fumes that smelled like car exaust coming from the vents but not as strong but enough to give us both headaches. He came, checked it out and said we had a cracked heat exchanger. Is it possible for a cracked h/e to make that smell? Would it be better for us to get the h/e repaired or get a whole new furnace. It is approx. 10 yrs old.