One time I used a hatcher without a fan. I borrowed it from a friend. The temp in the center of the incubator/hatcher was at least 5 degrees hotter than the edges. The chicks on the edge that had 3 days of "cool" had a hard time hatching and I lost some. Other were born with defects due to the temp fluctuation. If you incubator works well with the fan, I would recommend using it to hatch. No use messing with a system that already works.
If you have humidity problems, be sure to plug as many vents as you can. You can also mist the eggs with water to raise the humidity.