I live in Charlotte, NC and a friend of mind recently bought a new home. When visiting him, I noticed the vents around his crawl space were closed in the middle of summer. When I said something to him about opening them, he said his builder told him to leave them closed during the summer and open them in the winter. I was under the assumption that they were to be opened in the summer and closed in the winter. I have temperture controlled vents on my home, so his winter therory seems contradictory to this. So, which is correct, open in Summer or Winter?