That stuff is minor. For about $10,000 you can change it out, and you certainly will over the years. Budget about $1000 per year for a normal system, with repla

That stuff is minor. For about $10,000 you can change it out, and you certainly will over the years. Budget about $1000 per year for a normal system, with replacement every 10 years. The serious concern is ductwork. Replacement means ripping open walls, unless you go for the weird industrial look. Fixing your walls is not cheap. Normal ductwork grows a thick layer of toxic black mold. Normal ductwork is impossible to scrub clean. Good ductwork has a hard and perfectly smooth inner surface. It can withstand vigorous scrubbing. It is made of bare uncoated metal that is corrosion-resistant and mold-suppressing. Nickel and copper are great.