[Grog]

Go to the cobra vent website, or look up roof ventilation. There is a ratio between roof vent and soffit vent area. Can't remember the exact ratio but, you need more soffit than roof vent area to prevent drawing a slight vacuum on your attic space, and pulling air out of your living space. I had to go with a powered fan because I lacked the required ridge length to get the proper vent area. The PO of my house also short circuited the ridge vent by installing a ride vent on a ridge that was about 3 feet lower. The poor ventilation on my newly purchased home cost me a summer's worth of my time and $7k to replace rotted rafters, sheathing, roofing etc....