I am in a new home that is approx. 3400 sq. ft. and have 2 a/c units along with foam insulation. Had major issues/differences with HVAC installer regarding fresh air which resulted in him quitting after roughing everything in. He did not believe fresh air was needed but reluctanly ran vents from the outside into the air handlers. (foam installer refused to put the insulation in the house without fresh air) My issue is that my son has asthma and we all have allergies which makes me worry about the IAQ. Wish I had seen this site while I was building. Interested in all opinions/suggestions regarding this issue. We live in the deep south where it is hot and humid. Thank you very much.