How to Properly Seal Vents with Silicon between the Plenum Box and Drywall

When it comes to installing a new air vent or air register, there’s a lot to consider. Importantly, a tight seal will help mitigate the risks of leaking air which can, in turn, support the system’s effectiveness and energy efficiency. 

How is it carried out? When replacing vents, there arises a prime opportunity to seal your roof heat from the HVAC system. When paired with a properly sealed duct system, this becomes a vital component of an HVAC system that is both effective and efficient. But how does one go about sealing vent covers with silicone between the plenum and drywall? Let's dive into the process.

Understanding The Components

To carry this process out, it’s important to define a few components that we’ll be mentioning. These include:

  • Plenum Box: a plenum is a part of your ductwork, and in this context, refers to the box to which your air vent is attached and connects via a long insulated tube that connects to your HVAC. This might be in your ceiling, floor, or even wall, depending on your home or business ductwork. 

  • Air Vent: also referred to as air registers, linear air vents, HVAC grilles, linear diffusers or, AC registers, depending on their specific configuration, this is the vent that allows air to pass through the plenum into the room. 

  • Drywall: This is the material from which indoor walls and ceilings are typically constructed with before taping and floating. 

Getting Started

To begin with, there are some things to take into consideration. For example, are you installing a new modern vent, or simply removing the old one, sealing the area, and replacing it? In either case, your first step is typically to turn off the system. Next, you’ll want to carefully remove the existing air vent. Typically fastened with screws on 2 sides or sometimes 4 sides, this can require some care and attention. Use eye protection, and consider using a face mask to protect yourself from any debris. 

Cleaning The Area

Next, after the air vent cover has been removed, it’s time to prepare the area for proper sealing. Start by inspecting the plenum box that the air vent cover was covering. Look for any existing sealant around the edges, and take careful note of any gaps left between the plenum and the drywall. If there’s any old sealant, carefully remove it using a utility knife or sealant-removing tool. Next, carefully wipe the area down with a clean damp cloth to remove any dirt and debris. You also may be able to use a specialized cleaning solution formulated for this task. 

Adding Sealant 

After you’ve carefully cleaned the area, ensuring that any leftover debris, dirt, or grease that could stop the silicone from adhering properly has been removed, it’s time to apply the new sealant. Ensure that you choose a sealant designed for this task specifically; silicone sealants can be formulated for a wide range of tasks, so it’s important to choose one formulated for HVAC and drywall tasks. 

After you’ve opened your silicone sealant tube and have your caulk gun ready (the caulk gun is the tool you place your silicone sealant tube in), with a carefully cut 45-degree angle on the nozzle, start in one corner, and gently squeeze the trigger consistently as you slowly pull the nozzle around the entire vent. Let up on the trigger just before you arrive at the last corner so that the last pressure can be expelled right into the corner. If applicable, use a wet finger to smooth the final corner into the first corner. 

Final Steps

Once your sealant has been applied, it’s time to play the waiting game. While you may be tempted to replace your air vent, don’t do this immediately. Instead, consult with the instructions on your sealant, and leave the HVAC system turned off until the sealant is properly set. This can take up to 24 hours, but should be fine after 6 hours, but it’s always best to carefully read your instructions about curing time. 

Once the sealant has been allowed time to cure completely, you can reattach the old air vent or install your new one. Carefully fasten each attachment point, and then turn your HVAC system back on. 

The Bottom Line

Sealing your HVAC system properly is important. This allows the system to enjoy optimized efficiency, and will help mitigate the risk of unintended consequences of air leaks, sweating, and condensation which can lead to pathogen growth. When it comes to creating a good seal, one often important task is sealing the air vent by closing gaps left between the plenum and the drywall. By utilizing the right tools and materials, it’s often possible to create a tight seal using silicone, here. 

Remember, if you’re looking for linear vents or modern AC vent covers, at we’ve got you covered. Whether you’re looking for sleek, modern, linear slot diffusers to update the space, or you’re looking for a refreshed update with modern AC vent covers, we have a wide selection of standard sizes, available in both black and white — designed to suit a wide range of styles and needs. To see the difference for yourself, check out our extensive selection online today! Get in touch today to learn more. 

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