As I mentioned in my previous post, the Four Schools of Thought for Ceiling Register Placement are 1. Register Over the Window, 2. Register interior to room., 3. Register in Center of Room, and 4. High Sidewall Register.  All four schools of thought can work just fine (in terms of comfort), when done correctly.  Comfort, however, is not the only factor to consider.  Energy efficiency, materials efficiency, ease of installation, and aesthetics are all things to consider as well.  This post will look at all of those factors for this particular school of thought: High Sidewall Registers.  By the way, unless I say otherwise, I’m focusing on cooling mode on a very hot day. 

If I were designing my own house and had to choose between one of the four schools of thought, this is the one that I would probably choose.  Actually, the house I’ve designed in my head that I would like to build for myself would have floor registers, but between the four schools of thoughts for ceiling registers, this is the one I would choose.  Ok, Ok, I already admitted that high sidewall registers are not ceiling registers, but they fall into the category of having ducts overhead.

Sidewall registers should always be the “bar type” registers.  These are designed to throw the air roughly perpendicular to the surface they are mounted in, as opposed to ceiling register that have a throw distance measured parallel to the surface they are mounted in.  Bar type registers are designed to handle roughly twice the airflow of a low-end stamped face register of the same size and at a similar sound rating and pressure drop.  You also get much better throw distances.

The air can be directed across the room toward the load.  It travels in the upper unoccupied zone of the room and has plenty of time to mix with the room air.  This helps prevent cold air from blowing directly on people.  Something else interesting occurs called “entrainment”.  This is when the stream of air coming out of the register pulls room air up toward it, improving mixing and distribution.

On the negative side, the worst part about high sidewall registers is getting the duct to the back of the register.  I cheated on my diagram.  I confess.  I do not show the duct that serves the register.  In the previous three examples, true ceiling registers, it is obvious.

There are two basic ways to get the duct to the back of the high sidewall register, one works very well and one does not, but both require some extra steps that some architects and/or framers will not like.

The most common method is to drop a short rectangular can down the wall, in between the studs.  This is not a good idea for a lot of reasons.  1. The fittings are expensive.  2. There are a lot of extra feet of equivalent lengths in those fittings.  3. The typical stud bay is 3.5 x 14.5 inches.  A rectangular sheet metal can of that size is barely equivalent to a 7” duct and that’s if you don’t insulate the metal.  4. The top plates of the wall have to be cut out.  This weakens the wall structurally.  5. The sheet metal fittings can make noise when they heat up and cool down.  This is called “oil canning”.

The better way to run ducts to the back of a high sidewall register is to have the room being served have a higher ceiling than the adjacent room and run the duct above the lower ceiling. 
For example.  If the bedroom had 9’ ceilings and the hall had 8’ ceilings, this leaves a 1’ area at the top of the wall that the register can poke through and the duct can run straight into the back of a standard boot.  Another idea is to drop the ceiling of closets.  All of these, of course require a cooperative architect who is willing to do this.

So that wraps up the four schools of thought on where to put ceiling registers.  Don’t hesitate to leave a question or comment.

Coming up next:  Duct Size vs. Air Flow – Misconceptions Shattered Here.  STAY TUNED!