There are two visible accessories most homeowners associate with their HVAC systems. The first and most obvious is the thermostat. We do a great job educating customers on the benefits of upgrading their thermostats. It’s a natural add-on sale offered by most contractors.

The second most visible accessories noticed by homeowners — yet overlooked by many HVAC companies — are registers and grilles. In the typical home, registers and grilles are often unattractive to customers. In addition, some of them destroy air distribution in a room.

Is there an opportunity for you to better serve your customers by addressing these forgotten accessories? Let’s look at how you can increase comfort and profits by offering register and grille upgrades.


Over the past 40 years, the most inexpensive registers and grilles were typically installed in new construction homes. Many assume their only purpose is to cover the rough openings from the supply and return duct systems.

The idea that registers and grilles are just covers leads to many customer complaints. If you’ve ever experienced complaints about stuffy rooms or uncomfortable drafts, or found return grille vanes that were adjusted with needle nose pliers or magnetic scoops on supply registers, you know what I’m referencing.

Plus, most residential duct systems are sized using generations-old rules of thumb. Due to such rules of thumb, many duct systems are undersized. Register and grille sizes based on these undersized ducts often fail to deliver adequate air into larger rooms and overfeed smaller rooms. When you understand that registers and grilles need to be sized for the airflow needs of a room, their roles become clearer.  


One simple correction to many comfort-related issues is a supply register upgrade. As the years go by, registers get stepped on, painted over, and closed off. Besides these obvious problems, supply registers have another purpose to consider.

A well-placed supply register delivering 100 cfm of airflow can easily condition 1,000-2,000 cubic feet of room air. Higher-velocity supply air blowing from the register joins with room air and mixes the two airstreams together. This is commonly referred to as air entrainment.

How well air entrainment is accomplished depends on how well the register allows air from the duct system to mix with air in a room. As air leaves a register, it’s compressed and forced through the vanes or louvers. This action causes an effect similar to placing your thumb over the end of a water hose; it causes an increase in velocity.

If registers are smashed, restricted, or undersized, this velocity increase doesn’t happen properly and room air isn’t set into motion as it should be. This causes large temperature variations in a room, air that seems stagnant, or drafts resulting from excessive air movement. This is important to remember when weighing choices between upgrading registers or grilles: Registers almost always influence air movement more than grilles.

You should also consider air “throw” and “spread” when upgrading supply registers. These terms reflect how well a register distributes air into a room. Throw is the distance air travels from the register into a room, while spread is the maximum width air travels from the register.

Certain replacement register designs can hinder throw and spread by restricting the area available for air to pass through. Do your homework before offering them. If throw and spread are considered when sizing registers, they have a greater chance of performing correctly.

For those instances when drafts are troublesome, look for registers with adjustable vanes, as they allow you to direct airflow away from customers and toward areas of heat loss and gain, such as windows.

Register upgrades aren’t a cure for every situation. There will be times when additional duct repairs are needed to properly condition a room.


While return grilles don’t influence air movement as much as supply registers, you should still consider them in upgrades. Just like a supply register, account for the opening size to ensure the grille is quiet when the system is running. We’ve all heard return grilles sing when the fan is running. This is a clue too much air is moving through the grille.

If you hear singing, look for a less-restrictive return grille with larger openings between vanes. In certain situations, you may need to increase the size of the return grille or add an additional duct or grille back to the equipment. The goal is to relieve pressure and allow airflow a less restrictive path back to the fan.


You should also pay attention to filter grilles — not only noise issues but also air filter performance. Undersized filter grilles allow air to move through the filter too quickly. This causes dirt and particulate to move around the filter instead of through it, which reduces its effectiveness.

An easy rule for correct filter grille sizing is to allow 2 cfm per square inch of filter area. This keeps air speed at the filter in an acceptable range and keeps noise to a minimum. Using this simplified rule, a 20-by-20-inch filter grille (400 square inches) is the best size to handle 800 cfm of airflow. How often do you see 20-by-20-inch filter grilles on 2-ton systems?


Further answers regarding the performance of a register or grille can be found in the manufacturer’s data. It is common for register and grille manufacturers to publish these data on their websites. You should review and store this information in a place that can be easily accessible in the future.

Registers and grilles provide opportunities for you to easily solve comfort issues and make upgrade accessory sales that may have been overlooked previously. By understanding the impact these accessories have on HVAC systems and the air distribution in rooms, you create a win-win for you and your customers.

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Publication date: 9/26/2016

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