There are millions of old homes that need to be retrofitted for AC. They don’t have duct work because they are heated by radiators. When they are upgraded to ha

There are millions of old homes that need to be retrofitted for AC. They don’t have duct work because they are heated by radiators. When they are upgraded to have AC they often have 2 (or more) units since running ducts up and down isn’t feasible. So for the first floor you run ducts in the basement and vent up. For second the coil is in the attic if possible and vent down. These types of homes often have 100A service and running 3t + 2t already stress it. People also do it for efficiency reasons. Running hot/cold air long distances is a good way to waste money. It’s also better design to have multiple units and therefore multiple zones. Why are you cooling your bedrooms all day and your living room all night? Installing multiple units is better design but cheap builders just try and keep prices/quotes low to customers that don’t understand it.