As promised, here are the “Four Schools of Thought on Ceiling Register Locations”.  See diagram below.  OK, so the fourth option is technically not a ceiling register, but it is often used as an option.

First some assumptions: 1. slab on grade house, floor registers are not an option; 2. It is a standard sized bedroom with a door on one side and a window on the opposite wall; 3. the return grille is outside the room; 4. the diagrams show cooling airflow (heating would be similar.

The blue arrows are the primary flow direction, which is the direction of the airflow caused by the velocity and momentum of the air as it leaves the register.  The purple arrows show the secondary flow direction, which is the direction of the airflow after it has lost its initial velocity.  Another way to think of secondary flow direction is the direction the air already in the room moves right when the system fan turns on.  Generally speaking, this is the direction the air is going to go to reach the return grill.

I’m sure all of you are dying to know which one of these is the best!  Well, I hate to burst any bubbles but, when done correctly, they all are very, very close.  They all have pro’s and con’s, which will be discussed over the next few posts, but in terms of comfort, which is based on even temperature in the room, they are all very close.

Notice that I was very careful to say “when done correctly”.  It is very easy to screw up any one of these by using the wrong type of register.  The first option should always be a two-way register, never a three-way or one-way.  The second option should always be a three-way, but one-way registers can work too.  It should never be a two-way.  The third option should always be a four-way, possibly a three-way or circular (radial) register.  The fourth option should always be a bar-type register directed perpendicular to the wall.