Parts, LONG PartsPros, Grilles

Supply and Return Grilles: What's the Difference?

When it comes to ventilation, there are 3 types of covers generally used for HVAC systems: grilles, registers, and diffusers. Of the 3, grilles are are the simplest in the sense that they don't involve any moving components, making them easy to install and maintain. Depending on your situation and needs, there are 2 types of grilles to choose from: supply grilles and return grilles.

Supply Grilles

Supply grilles will typically be deflected so that you are able to direct the airflow needed to a specific area. For instance, you would want to put supply grilles for air conditioning somewhere higher, as cold air falls, and vice versa for for heating – those supply grilles should be placed lower on the wall, as heat rises.

Return Grilles

For return grilles, the degree of deflection is not necessarily important unless you are trying to conceal what is in the vent behind the grille. Most commercial applications utilize light shields that affix behind the grille, or a double deflected grille, so that the view is relatively obscured.

It is essential that your return air vents are not blocked. Most HVAC systems require constant airflow to work properly, and a blocked vent could cause your system to either lose efficiency or fail earlier than it should. Some of the most common blockages include placing a couch or other furniture in front of the vent, as well as curtains, which can get sucked in and inhibit airflow.

If you need to replace a grille but are having trouble identifying if it is a supply or return, there is a simple test you can run. Hold a piece of paper up to the entrance of the vent. Once the system fan is turned on, pay attention to the direction the paper goes. If the paper is pulled toward the vent, then it is a return vent. If the paper pushes away from the vent, towards you, then it is a supply vent.

A messier, but more fun, experiment to do to understand airflow in a room is to use a powder of some type, such as baby powder, and have it placed into your supply vent. Once the air is turned on, you will see the airflow pattern that develops in the room! The cleanup this requires does make it a more impractical experiment to conduct, but it is certainly effective!

Of course, the simplest way to determine your exact grille needs would be to contact a LONG PartsPros representative and describe the systems you are using, along with your intended usage, or send in pictures so we can get a better understanding of your situation. We will gladly assist and take out all the guesswork for you!

And if you already know what grilles your need for your HVAC system, you can order with us by calling 855-566-4778 or buy online at


Jonathan is the Materials Handler for the LONG PartsPros team, working in our warehouse in Littleton, Colorado.