Why are almost all of my house's HVAC floor registers placed near exterior windows?

Question

My current house is a single story built over a crawlspace and all the HVAC registers are in the floor. In all of the larger rooms, at least one (and usually more) register was placed near an exterior wall and almost always near a window. Looking throughout the house, it seems intentional. I've noticed this before in other houses, and I've talked a few friends and the informal poll tells me that for houses with floor registers built in different states built decades apart, it appears the registers were intentionally placed near exterior windows. In my case, given the layout of the crawl space, it seems like it would have been easy to place them them in other locations.

My amateur intuition tells me that for both heating and cooling, having registers near a window is going to lead to a lot of waste. Is this layout actually common? If so, why?

Answer 1

Yes, placing registers (or other heat sources such as radiators) near exterior windows and doors is the usual practice. This is done in order to combat cold drafts and ensure a more even temperature throughout the room. Here's a Q&A on the subject from Ask This Old House:

Window glass is the coldest part of a wall. When warm room air hits it, the air cools, and cool air sinks. The movement of cool air creates floor drafts that most people find uncomfortable. The placement of forced-air heat registers or baseboard heating units under the windows counteracts this process by sending up warm air to mix with the cool. The end result is that the room feels more comfortable.