A Guide To Soundproofing Air Vents In Your House

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Guide To Soundproofing Air VentsWhen I first moved into my new house, I decided to soundproof my bedroom.

I worked on the doors and windows first and then treated the walls for soundproofing. 

After all that hard work, I still had sound leakages and realized that the air vents had been left out.

This post is meant to be a guide to soundproofing air vents in a room. So I will discuss some of the methods I used which helped me.

Flanking Noises

While researching on methods of reducing sound coming from vents, I came to know what flanking noise is. Flanking noise is basically sound which enters a room from paths other than the wall separating the room from another room or outside.

Some examples of flanking noise are:

  • Sound from air vents that are meant to use ambient air to cool the room.
  • Noise through the ductwork of the HVAC system.
  • Noise from the doors and windows through indirect paths.
  • Sound transferred through interconnected floors, ceiling, and walls.

As this is a guide to soundproofing air vents, we will talk about tackling the first two issues above, which are:

  1. Sound from air vents that are meant to use ambient air to cool the room.
  2. Noise through the ductwork of the HVAC system.

Soundproofing Normal Air Vents (No HVAC)

By saying “normal air vents”, I’m referring to those vents that are above a door or window and serve to let in outside air. There are two solutions for dealing with these types of air vents which pass sound easily:

Option 1 – Remove the vent

The first and ideal option is to remove the vent completely and plug the gaps with sheetrock on both sides of the wall and the insulation in between.

Modifying the vent itself will not yield results. If you need the air vent for cross ventilation and during the summer season, it is better to install a soundproof window (read my article) that can be opened whenever ventilation is required.

I have read of an alternate solution which involves having a maze kind of a box which will make it difficult for sound to travel through. I am not convinced that this is a good option for isolating non HVAC vents as you will need a pretty long box for any useful effect.

Anyway, since I have not tried it, I cannot rule this option out, so I will neither recommend nor oppose these ‘sound mazes’.

Option 2 – Cover the vent

This option is similar to the first one because essentially, we are doing the same thing. This option is for those who cannot or are not permitted to remove the vent for some reason.

Just cover the vent with heavy MDF or drywall. Two layers with Green Glue in between would be better. After that, use an acoustical caulk to seal layers between the existing wall and the new layer of MDF or drywall.

With this, we are eliminating the prime cause of sound transfer which is air gap. By adding MDF or drywall, the extra mass will help in noise isolation.

The drawback with this option is that it will seal the room making it uncomfortable in summer months. The room will not have cross ventilation either, but if you have air conditioning available, this will not be much of a problem.

Soundproofing HVAC Vents

The issues related to sound coming from the air vents of an HVAC system are complex and not easy to deal with.

However, there are a few solutions which can be incorporated to reduce sound entering the room:

1. Upgrade the HVAC system

If you have a noisy HVAC system running on old technology, consider upgrading it to a more advanced system which is less noisy. Modern systems are more energy efficient too and this will be an added benefit.

2. Duct Liners

A cost-effective way is to use lining for the ducts to insulate the sound. Duct liners have an insulation material which will reduce the amount of sound reflecting from the inner walls of the duct.

The insulating material is inside the walls of the duct and has a lining on both sides. Without the lining, the air flow in the duct will blow glass wool fibers into the room.

The duct liner I would recommend is Reflectix (check price on Amazon) which is cheap and effective. A 25-foot roll would cost under 30 dollars.

3. Flexible Ducts

guide soundproofing air vents flexible duct

Flexible ducts are useful but they should be used only where they are required. A flexible duct can be bent and this is beneficial for sound reduction.

By having the duct bend at various places, you’re making it difficult for sound to travel through the air flow.

The only drawback is that the bends in the flex ducts may have small breaks in them. That is why they should be used in quieter places so that sound does not enter the duct.

As a precaution only use a good quality flex duct like the one from Dundas Jafine (check prices on Amazon) so that you don’t have to worry too much about this.

4. Soffits

For all ducts exposed to direct sound, we will need to cover them with sound insulating soffits.

A typical soffit for this application would be one made of MDF with a layer of insulation in it. Soffits of this type are a must-have in home theater installations.

Some home theater enthusiasts also add layers of drywall with Green Glue (viscoelastic damping) in between them. But that is required in dedicated HT rooms which require a high degree of soundproofing.

The flexible duct inside the soffit will have a lot of bends so that we can achieve a better sound reduction.

5. Create A Sound Baffle

A Baffle would typically consist of a box which forces sound to travel along a bent and elongated path.

The box is like a maze with sound absorbing materials on the inner walls. Sound gets absorbed on the way as it travels the complex path.

I found these baffles to be very effective for soundproofing. Running the flex duct along the crooked path and then sealing the box gives even better results.

As I had mentioned earlier, these baffles are only good for HVAC vents. Owing to the large duct lengths, sound can be controlled as it travels the longer route. However, if you want to soundproof a normal vent above the door, the baffle is not good enough.

6. Get Professional Help

If you are going to make some major modifications to the size and length of the duct work, professional assistance is strongly advised.

Summarizing This Intended Guide To Soundproofing Air Vents

When it comes to soundproofing, there are not many effective quick-fix solutions. This is true whether you are soundproofing a wall, door, ceiling or any other surface.

What has been mentioned here is not based on my knowledge and personal experience alone, but has also taken into account the advice of soundproofing experts on Avsforum and other platforms.

Soundproofing air vents, especially for an HVAC, can be simple or complex depending on your layout. In some cases, a little bit of duct lining will do. Identifying the main problem areas is important before you start.

For normal air vents, we would be better off blocking them completely. For HVAC, if you follow the principles in this guide, I assure you that you will not be disappointed with the results.

Check out my recommended insulation materials for soundproofing and acoustics.



Through several years of research and experience, I can say with confidence that I have acquired substantial expertise in the field of soundproofing. I only put out information which I know is genuine and is backed with research. Read More About Me..