We are near Colonial Beach, VA and have a 1282 sq ft manufactured home that has a 550 sq ft open area. In the open area it has a 9ft high vaulted ceiling. There are two 14"x5" rectangular runs of 45-50 feet in length. There are 12 floor vents. 5 of those floor vents are in the 550 sq ft open area. In the link below is what we are considering.