Air deflectors on floor registers and cooling efficiency

Question

I was once told by an HVAC technician to avoid using air deflectors on floor registers during the summer. The reason was that the last thing you want to do is to direct the heavier, colder air towards the floor. Doing so prevents the fresh cold air from mixing with the stale warmer air before it inevitably sinks.

Makes sense, but i have since seen (and heard) a couple of counter arguments to this:

• Most homes tend to leak air around the exterior walls and windows, which is where many floor registers are located.
• Blowing cold air up a warm exterior wall is not desirable and tends to create hot/cold pockets, especially in large rooms. Doing so could also cause undesirable condensation/moisture problems on the the exterior walls/windows.
• Part of the cooling effect is our perception of it, and air deflectors help us feel cooler by making the air flow more directional towards the main living space.
• Heavy curtains and other window treatments often impede or trap the cool air that blows straight up from a floor register.

For the experienced HVAC pro's and hobbyists here - what is the verdict on air deflectors? Do they help or do they make your cooling less efficient?

Answer 1

The past home owner left these in my place. Where the blowing air just gets caught behind the curtains, is under furniture or tropical plants, I divert it, and this just happens to be towards places where people sit.

Keep in mind in the winter, having the warm air low helps mix it. But in all seasons, the vents are near windows and doors to counteract the cold/hot spots these create to give you a more even temperature in the home.

Also, if you have moisture problems in your windows, it's not because of these deflectors. Well insulated windows (multiple panes and weather stripping) are the solution to that problem.