One of my biggest peeves is the placement of ac/heater registers on the floor right under a window. The warm/cold air you’re paying to produce is being negatively affected as soon as it rises out of the register. Older windows, especially aluminum/metal windows, represent one of the weakest points in your home’s defense against the outside air temperature. If you have registers under windows, try replacing their covers with directional covers or use a magnetic deflector. These devices will direct the forced air flow away from windows and more toward the center of the room which allows it to affect your indoor ambient air with full power versus having it chilled or heated by air temperature around windows. If its inconvenient or you have trouble finding one of these, I’ve included an amazon affiliate link so you can have some of these delivered to you. Just unwrap it and set it right on top of your existing register making sure the air flow is directed away from the wall or in the direction you want the air to flow.