Vapor wear If the exterior vapor barrier on a heating, ventilation and air conditioning -- or HVAC -- duct is damaged, the insulation eventually will go too, making the entire system less energy-efficient and more costly to operate. If you can't make the repair yourself, hire a qualified HVAC technician to do the work. The end result will be increased utility expenses and decreased levels of comfort. The owner should replace this damaged duct work or hire a qualified HVAC person to recommend proper actions.