Should Return Air Vents Face up or Down

There is no proper direction for the vanes to point. If they’re high sidewall, normally they would be pointed upward which makes them vision proof and just the opposite for low sidewall.

Do air return vents go up or down?

In the winter you want the cold air to be drawn through the return registers leaving the hot air behind. By opening the lower registers and closing the top ones you keep hot air in and draw the cold air out. Since cold air is heavy it will automatically flow down to the lower register.

Should heat vents face up or down?

A downward direction is preferred more, as air always rises up after collecting heat from below. The velocity of air will have to be low and linear by the time it reaches occupants.