How to Soundproof an Air Vent (Inside or Outside)

soundproofing an air vent

Last updated: January 21, 2022 at 11:28 am

Soundproofing an air vent can be a little tricky. However, it’s well worth looking into as some vents can cause excessive noise.

In this article, we’ll run through 8 different ways you can soundproof an air vent and explain what causes excessive noise through the vent.

Remember:

Make sure you don’t block any vents which are there to remove any harmful gasses from your home!

Why Would You Need to Soundproof Your Air Vents?

If you live in an area where air conditioning is a necessity, it’s likely you’ll need to run it for long periods to keep your house at a comfortable temperature.

Noisy air vents may not be a problem during the day when the everyday sounds mask them, but at night when trying to sleep, they can be a big issue.

What Causes Air Vent Noise?

Rather than direct sound, noise from air vents tends to be flanking noise. If you’ve never heard the term, flanking noise is a sound that enters a room from some other way than passing through the walls. This includes:

  • Sound that comes in through doors and windows
  • Noise that travels through connected walls, ceilings, and floors from other rooms
  • Sounds from external air vents that lead outside the home
  • Sounds from the ducts in the HVAC system

The three main components that impact air vent noise are the shape of the vent, what the vent is made of, and how many walls intersect with the vent.

Materials such as metal are far more likely to reflect sound and create a louder noise. If there aren’t many corners, then the sound will travel easily along the ducting and be louder when it emerges from the vent. On the other hand, if there are lots of corners, then as the sound wave hits each one, a little of its power is absorbed. So, the more corners the sound wave must navigate, the quieter it will be when it emerges into the room.

This process will be increased if there are also lots of walls inside the ducting as this will also bleed off some of the sound wave’s power. So, if noise is a concern, having a vent made from a flexible material with plenty of bends and turns will significantly reduce the amount of sound that will emerge from the vent into the room.

8 Ways to Soundproof Your Air Vents

There are several different options, and which is best for you depends on if your air vents are part of an HVAC system in your home or just vents that lead directly through the outer wall of your home to let fresh air in from the outside.

Remove the Vent

A vent that leads outside may not be effective. For example, if your home is too warm because of a high outdoor temperature, all the vent will do is allow more warm air in. There will be cold air coming in during winter, which is the last thing you would want. So, if you feel you’re getting no benefit from the vent, then sealing it up will prevent external noise from entering your home.

The easiest way to do this is to remove the vent and seal the gap up with plasterboard. If you want to enhance the effect, you should use two pieces of plasterboard with soundproofing material sandwiched in between. Good choices are green glue soundproofing compound or mass loaded vinyl. You could also consider using acoustic plasterboard either on its own or with the additional material. How much mass you need depends on how much noise you’re trying to block.

Create a Sound Maze

air vent sound maze

This step refers to HVAC systems rather than stand-alone air vents. As explained earlier, the more corners your ducting has, the more the power of the sound wave is reduced. So, in any room where noise from the vents is an issue, you can create a maze to minimise sound.

Firstly, remove the vent cover. Then you need to build a series of 180-degree bends behind it. You can do this with plywood, but, if possible, use flexible ducting. Flexible ducting is great in that it’s easier to mould into shape. However, it is a little more prone to splitting, which can let sound escape, so buy a good quality brand and fit it carefully.

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If you’re using plywood, you should measure the vent and cut pieces to size. You’ll need to cut a section off the top to allow the air to pass through; 25-30% should be right. Glue acoustic foam on all the sides of the ducting and wait for it to dry.

While you’re waiting, glue more foam on both sides of each panel or alternatively glue on mass loaded vinyl. Carefully apply glue to the sides of the panels and fit them in the duct. You should aim for a minimum of four panels to get the best effect, but the more, the better. Fit the panels an inch/2.5 cm apart.

Cover the Vent

If you find that your vent is necessary at times and don’t want to remove it altogether, then another option is to cover the vent. You won’t want to use anything that’s difficult to remove, so good options here are soundproof blankets, moving blankets, thick curtains or even furniture.

If the vent is above your window or door, then hanging a blanket or curtain that covers the vent and the door is a great idea. Firstly, it will be easy to pull back or remove when you need to use the vent. Secondly, if the blanket covers the door, then it will cover any gaps around the frame and the gap between the door and the frame. Finally, it will further enhance the soundproof effect and keep heat in during cold weather. As winter is when you’ll want to close the vent, this is ideal.

If the vent is nearer the floor in a place where you wouldn’t want to hang a curtain or a blanket, then your best option is to put furniture in front of it. A well-upholstered sofa or armchair will absorb a lot of the sound emerging from the vent, especially if you place it quite close.

If the vent is narrow and close to the floor, you could even put a draught excluder across it. They come in a range of shapes and colours so you could find one that matches your room, or if you’re crafty, you could make it yourself.

Fit Acoustic Foam

Even if you don’t decide to build a sound maze, fitting acoustic foam is still a good fix. Technically it isn’t a soundproofing material, so it’s not normally recommended for other soundproofing projects.

Cinemas and theatres are the main venues that use it to reduce echoing. As ducts cause sounds to bounce and echo, the acoustic foam will stop the echoing from amplifying the sound.

Use Duct Liners

air vent duct liner

If your HVAC system is generally in good condition, just noisy, then you can fit duct liners. They are both cheap and easy to install, making them an ideal first step. They’re made from soundproof material, which will absorb vibrations and noise caused by the ducts.

The liners have two sides to stop fibreglass particles from being blown into the room. The fibreglass side sits against the wall with a protective lining facing into the ducts.

Create a Temporary Cover

Take off your vent cover and measure inside the vent. Cut out two pieces of plywood and sandwich them with green glue or mass loaded vinyl. You can leave it like that or cover it with paper to make it look neater. Consider using a piece of wood or a doorknob to make pitting it in the duct and taking it out easier.

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To improve the soundproofing even further, you could install weatherstrips around the vent to ensure the cover fits snugly.

Get Your HVAC System Serviced

Any complex system will start to break down over time. If your HVAC system is old, it’s worth calling in a professional to check that it’s still in good working order and does not need to be repaired. Sometimes fixing minor cracks and defects can make a big difference to how loud the system is and how well it works.

Upgrade Your HVAC System

This should be your final option as it is very expensive to replace an entire system. The average cost is around £5,000, so it’s not a small investment. However, if your system is old, it is probably quite inefficient and costly to run. If your system is old, gaps and cracks will cause hissing and buzzing noises. This leakage will also make your system less effective.

If you decide to go down this route, get at least three quotes to ensure you’re being charged a fair price. Look for reviews online and, where possible, ask for recommendations from friends and neighbours so you can feel secure the tradesman will do a good job.

Rounding Up

So there you have it, 8 relatively easy ways to soundproof an air vent. Whichever method you choose, make sure you weigh up how much noise it’s making compared to how much sound reduction each method can achieve.

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About the Author: AJ

AJ is a self-confessed soundproofing nut. He has written full-time on Quiet Living for the past 3 years, and has a wealth of knowledge about living a quieter life, soundproofing and fixing loud noises.

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