I have a Arcoaire RPJ II furnace, built in 1996. Actually I have two of them... one in the basement and one in the attic. They support 16x25x1 size filters. But I am confused about what Merv rating to get? I heard that if you go too high, it can restrict airflow too much. And if you go too low, it can damage the furnace. We suffer from airborne allergies in our household. Plus we have a pet cat. What Merv rating filter should we use?