GRD Terminology


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GRD Terminology

A Toungue-in-Cheek Terminology Tutorial and Call to Action

by Ben H. Dorsey III, Vice President of Marketing
As published in the "Air Distribution & Movement Supplement" to the ACHR NEWS

It seems as every industry matures the terminology used by industry professionals becomes more specialized. However, within our industry, we speak of air distribution products with a fair amount of non-specificity. This is especially true in regards to grilles, registers, and diffusers. Since we’ve been making these devices for more than a century, perhaps it’s time to finally come to a consensus.

Perform a simple Google search for these terms and you’ll discover the most overly simple to overly complex to downright incorrect definitions. And that’s after sorting through pages and pages of inapplicable definitions.

So often from the public we hear the term, vent, simply because it’s an easy, generic word to use. Even within our industry, it’s not unusual to hear the term, hole cover. Now that’s just plain lazy!

On one contractor web site, I found this definition for grille: “Same as Air Diffuser. May also be called a register.” Really?

And even when we want to be a little more accurate, we’ll use the general abbreviation of GRD, for grilles, registers, & diffusers.

So, let’s tackle the terms in that order.


This simplest device in terms of inherent complexity is, in application, more complex than the other two. A grille is simple in that it does not have an attached damper and, in most cases, has no moving parts. However, a grille can be used for both supply air and return air. The same is not true for a register or diffuser.

So here’s our definition: Grille—A covering for an opening through which air passes.

(Can you say ‘hole cover?’) But wait, wouldn’t that definition also be applicable to register and diffuser? Maybe our contractor friend mentioned above was right after all?

I like to think of it in the simple geometric language we learned in school. You remember: A square is a rectangle but a rectangle is not necessarily a square. By the same token a register is a grille but a grille is not necessarily a register.


Let’s get right to the definition: Register—A damper-equipped grille which supplies conditioned air.

So we’ve taken our grille, added a damper and use the resulting product only for supply air. That’s a little more specific use. But the term “register” is still somewhat generic and is generaly appropriate only in the residential market.


With enhanced capability a register becomes known as a diffuser. Our definition is amended as follows:

Diffuser—An air flow device designed to discharge air in a spreading pattern, specific path, or particular direction.

So, once again, we’re talking about supply air and control of it. We’ve added specially designed louvers, vanes or stamped devices that can place air in thin layers, in circular patterns, or spreading jets—in essence a register on steroids. But what happened to the damper? Well, it’s there . . . most of the time. (Think of it as i before e except after c or when sounding like weigh.)

The Problem

The terms register and diffuser are often interchanged, even by product manufacturers. That is simply the result of generations of common usage. After all, a floor register has been called that for decades despite the fact that most really are diffusers. In the commercial realm, things are easier. Here, grilles and diffusers reign supreme and register is something you do before attending an event.

Our problem with trying to define these terms is two-fold: First, the lines really are blurry between them. And second, all these words have commonly used alternate meanings. (Just try setting up a Google Alert for news and information about grilles, registers, and diffusers and you’ll see what I mean. That one cost me a make-up lunch with my IT manager.)


The Solution!

So, I think we need a new term—a single word or short phrase that can be used instead of grille, register, or diffuser. I know what you’re thinking. We have such a term in hole cover. But I think you’ll agree that it lacks the panache befitting an evolved and professional industry.

No, we need a new word—dare I say it—a made-up word. It should be catchy enough to unite manufacturers, distributors, contractors, homeowners and facility professionals. It should speak to air distribution devices and encompass the function of all three devices discussed here. Further, it should be short and applicable to singular and plural usage.

After careful and thorough consideration (basically, between the time I decided to do this in the paragraph above and right now), I am prepared to advocate the use of the term, iVent.

It’s got it all—the “everyman” appeal and that cute little “i” that’s become so trendy. So let’s set aside a century of grilles, registers, and diffusers, and usher in a new century of iVent. I can already see the campaign theme: “It’s not just a vent; it’s an iVent.”

I hope I can count on your cooperation.

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