I am in process of buying this 6 year old house in Houston ( Currently in Option Period), and had the house inspected this weekend. Found Excessive Mildew Exterior of Plenum on and some mildew at register in study room. I think owners has not performed maintenance for many years. What do you folks thinks will be the extent and severity of issues to cause potential health issues to small kids in house. Is asking sellers to repair/Clean HVAC the way to go, or shall i just back out. I have read in some internet posting HVAC system will develop mildew no matter what.