My friends just moved into a new (to them) home and invited us to the housewarming party. I made the faux pas of critiquing their HVAC system. This embarrasses the heck out of my wife and happens far too often. It’s very hard not to say something when you know so much about how these homes were built. In our area, I can look at the type and location of the supply registers and tell you which HVAC company designed and installed it.

Probably 95% of production homes in CA (and likely all over) suffer from undersized ducts, which results in airflows below 350 CFM per ton or so. Some much less. In the 2013 version of CA’s energy code they mandated a minimum of 350 CFM per ton and 0.58 watts per CFM. Think of 350 CFM per ton as a D- grade. One CFM less is a FAIL. The other way to think of it is as the very worst airflow you can have and still meet code. When I was designing a lot of production homes, I designed to an absolute minimum of 400 CFM/ton and they regularly tested out at closer to 500 cfm/ton because I was pretty safe sizing ducts. More airflow is generally better, especially in hot/dry climates.

A real quick and easy way to improve airflow in these types of homes is to replace the cheap “stamped face” registers with a “bar-type” register. These may go by different names but, basically, a stamped face register is the most common style. The entire face and the fins are all from one piece of sheet metal that was stamped and the fins were bent in or out. Bar type registers have a rectangular frame, but each fin is a separate piece of metal that can be individually adjusted (without bending anything). Both Lowe’s and Home Depot sell both kinds. (Search “ceiling registers”on their sites.) The easiest way to tell them apart is price. Bar type registers are roughly twice the price of the same size stamped face, which explains why stamped face are the most common in most homes. But even at $15-$25 each, it’s a cheap way to really improve airflow. A bar type register is rated for roughly twice the airflow at the same pressure drop and sound rating as a stamped face. I’ve often measured up to 20% increase in airflow by replacing a stamped face register with a bar type, occasionally more. When I lived alone in an apartment, I took all the registers off completely and it made a huge difference! Only an bachelor engineering nerd can get away with that, though. (No, “bachelor engineering nerd” is not a redundant term.)

 

Bar Type Register – photo from homedepot.com

 

Stamped Face register – photo from homedepot.com

 

 

 

 

 

 

 

 

 

 

Here is link to a 10×6 bar type register sold by Home Depot: bar type register

Here is link to a similar one sold by Lowe’s: bar type register

Note that the size 10×6 refers to the size of the register boot behind the register. The dimension of the register itself is about 1 3/4 inch bigger in both dimensions. So if you were to go through your house and measure the outer frame dimension of all your registers, you would subtract about 1.75 from each dimension to get the nominal size (round to the nearest inch). They come in pretty standard sizes, usually even numbers, 12×4, 10×6, 12×6, 8×4, etc. They might also come in steel or aluminum. Aluminum is a bit more expensive. Steel is fine unless you live in a humid area. They perform about the same.

You can also sometimes buy directly from your local HVAC supply house. Tell them you want something comparable to a “Shoemaker 950 series (aluminum) or 951 series (steel) bar type register”.

The only tools you need are a screw driver and maybe a razor knife if the registers are caulked in place. Only do this project if you are comfortable working over your head while on a ladder and the registers are easily accessible. Be super careful. I’ve seen registers located 20′ above the floor. Leave those alone. Hopefully the screws holding the registers in place are going into wood and not just sheet rock. If not, which happens too often, you may have to use some sheet rock anchors.

I suggest only replacing the registers in the more important rooms, such as family room, master bedroom, etc. Smaller rooms like bathrooms and laundry rooms usually are getting plenty of air. If you have rooms where you’ve closed down a register, no need to replace those. Also, if you live in a two story house served by a single, non-zoned system (one thermostat) try replacing just the downstairs registers first. See if you notice a difference.

While you’ve got the registers off, take some caulk or expansive foam and seal the gap between the sheet rock and register boot (sheet metal box that penetrates the sheet rock and that the register slips into). Make sure you can get the register back in before the caulk or foam dries.

If you do this let me know how it came out! Good luck. Be safe.