I spoke with an HVAC guy over the weekend about just this topic. He said about 4 yrs ago, the state of CA required all new construction to have ducting that goe

I spoke with an HVAC guy over the weekend about just this topic. He said about 4 yrs ago, the state of CA required all new construction to have ducting that goes to and from, each room in a house. So when Jr. goes off to college, you can close the door and not send cool air to his room. I think he said it's something like 30% more efficient? But don't quote me on that.