What’s the difference between an AC Vent Cover and a Linear Slot Diffuser?

What is a Vent?

A vent in laymen’s term is the point where the air duct enters the building. This portion of the air duct system is the vent but is referred to as a plenum box or just plenum. An air duct encompasses any passage used to supply and/or extract air vertically or horizontally. So anything where air is being passed from point A to point B is called the air duct but the actual point A and point B are considered the vents or referred to as the plenum box. Most often these vents are made of fiberglass, but can be made of various materials.

plenum box
Plenum Box photo credit: TexasBuildmart.com

What is a Vent Cover?

The face of a vent is called a vent cover, because it covers the vent so that you wont be looking directly at the plenum box and see an ugly black hole. Sometimes, these vent covers can look plain, or look very complex and decorative. These vent covers are made of sheet metal, aluminum, fiberglass, wood, plastic and other various materials. The material doesn’t matter except that they cover the vent hole, so that the vent becomes visually appealing. The various names for the face of a Vent are Vent Cover, Register, Grille, Grill, AC Vent Cover or sometimes just Vent.

In our example, we will be talking about a home, where an Intake Vent (often referred to as the Return Vent) that is often located where the home furnace is, draws fresh, clean air into the furnace. Here the air passes through the Return Vent Cover, then through the evaporator coils which absorbs the heat of your home and then blows (via the blower) cool air throughout the home via the home’s air ducts. This air duct system is often made up of long flexible tubes that are insulated with fiberglass, metal wires, plastic, and vinyl (These long flexible tubes are often referred to as “flex”). Finally, the cool air passes through this flexible tube and ends up at a plenum box (which can be square or circular) and supplies the room with cool air. That’s why this vent (plenum box) is referred to as a Supply Vent. The last thing is the vent cover that covers the face of this vent (plenum box) that supplies the air into the room and why this vent cover is referred to as the supply vent cover.

A home AC Cooling System Diagram
A Home AC Cooling System Diagram

So to recap, hot air in your home is sucked in via the Return Vent and then passed through evaporator coils that absorbs the heat, cools down the air and then passes the cool air around your home which ends up at various Supply Vents around your home like the ceilings, walls and sometimes floors.

So what exactly does a Diffuser do?

Well, a Diffuser does just that, it “diffuses” the air. As we established before, the face of a vent and is called various names like Vent Cover, Register, Grille, Grill, AC Vent Cover or sometimes just Vent. A Diffuser is just another face of a vent, except it “diffuses” the air.

A Diffuser is any device used to direct the air at different angles by profiled blades. When the air passes through a vent with blades that can be manipulated, the air is being “diffused.” So essentially, an AC Vent Cover that has blades that can be manipulated or redirected is diffusing the air, and can be referred to as a Diffuser. NOTE: These blades that diffuse the air are often referred in the HVAC industry as Louvers

Different types of Diffusers
Different Types of Diffusers

What is a Linear Slot Diffuser?

A Linear Slot Diffuser is a type of AC Vent Cover that is the face of a vent to distribute conditioned air in a home. It consists of a long, narrow, horizontal slot that is mounted on a ceiling, wall or floor. They are designed to blend in with the surrounding architecture and can be found in office buildings, schools, hospitals, and other commercial and industrial buildings because of it’s modern architectural look. So a Linear Slot Diffuser is an AC Vent Cover that is long and skinny and diffuses the air by manipulating the blades (louvers).

Linear Slot Diffuser photo credit: texasbuildmart.com

So what’s the difference between an AC Vent Cover and a Linear Slot Diffuser?

  1. An AC Vent Cover doesn’t always diffuse the air like a Linear Slot Diffuser does. While there are AC Vent Covers that diffuse the air, not all of them do which is why a Linear Slot Diffuser isn’t simply referred to as another register, grille or vent cover.
  2. AC Vent Covers are often separated into two different vent cover types: a Return Vent Cover and a Supply Vent Cover, whereas Linear Slot Diffusers can often be used as both. Linear Slot Diffusers can be used for both the purposes of a Return or Supply vent cover because of the large space provided by the large slot openings.
  3. An AC Vent Cover looks boxy, large and bulky, whereas a Linear Slot Diffuser looks linear, long and skinny. See below for visual reference
photo credit: texasbuildmart.com

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