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There’s a lot of information out there on soundproofing air vents, some of it is good and some of it is bad. In this article I want to share some of the best methods that I came across, as it may help others soundproof their noisy air vents too.
During my research on soundproofing air vents I came across the term ‘flanking noise’. I had no idea what it was until I dug a little deeper. In short, flanking noise is when sound enters a room from paths other than the wall that separates the room from another room or outside.
Still confused? Here are some examples of flanking noise:
- Sounds from air vents that are normally used to cool the room with air from outside.
- Noises from the HVAC system ducts.
- Sounds indirectly traveling through the doors and windows.
- Noises transferred through interconnected floors, walls, and ceilings.
As we’re focusing on soundproofing air vents in your home we will look at the first two issues in the list, which are sounds coming from air vents and noises coming from the HVAC system ducts.
Before we jump in I want to just quickly run over the three main factors that affect noises coming from your air vents.
Factors That Affect Air Vent Noises
There are three key factors that will affect air vent noises, which need to be considered before taking any action. These are the following things:
- The shape of the air vent
- The number of walls inside the vent
- The materials the air vent is made from
To put it into perspective, if the inside of your vent is made from metal it is very likely the sound will bounce off the material and create noise.
Likewise, if there aren’t many walls inside the vent for the sound to bounce off then it will enter the room very easily, as it doesn’t get absorbed by anything.
This ties into the shape of the air vent, as more corners, will absorb sound better than a straight duct. For example, a flexible duct with lots of bends will reduce the amount of sound that reaches the end of the vent.
How to Soundproof Air Vents
Air vents can be categorized into two types – the standalone ones and the ones belonging to the HVAC system.
Standalone air vents refer to vents that are typically situated above a door or window with the purpose of delivering fresh air from outside the house. This doesn’t include vents that use an HVAC system (more on that below). There are a number of solutions you can use to deal with normal non-HVAC air vents and the annoying sounds that travel through them.
Standalone air vents can be made soundproof by either covering them with soundproofing materials or replacing them with drywall. To soundproof the HVAC system’s air vents, materials such as duct liners, soffits, and sound baffles are some viable solutions.
Here are the ways you can soundproof the air vents in your house. The first two pertain to standalone vents, whereas the remaining pertain to HVAC air vents.
1. Remove and replace the air vent
Removing the vent is perhaps the best option when it comes to eliminating sounds from an air vent. It’s simple, effective, and won’t cost you much money to do.
The best way to do this is by removing the vent entirely and then plugging the gaps with sheetrock on both sides of the wall and in the insulation itself.
You must remove and plug the entire air vent; simply modifying the vent won’t give you the results you’re looking for. If you really need the air vent for cross ventilation, for example during the warm summer months, you’ll be better off installing a soundproof window (read my handy guide here).
With a soundproof window, you have the benefit of being able to open it when you need ventilation, while still having some soundproof protection against external noises.
I did come across another solution which was to install a kind of box, containing a maze of foam and plywood, which would in theory absorb the vibrations from the sound. After considering this option for a while I decided against it. You would need to have a pretty long box to cover a non-HVAC air vent for it to have any meaningful impact on reducing sound.
However, I didn’t personally try this option, so perhaps it is effective in some situations. For that reason I cannot rule it out as an effective method of soundproofing, but I can’t recommend it either. If it sounds like an interesting option to you then you can find out more information by researching ‘sound mazes’.
2. Cover the vent with soundproof materials
This is another simple and effective method that is somewhat similar to removing the vent. If you’re unable to remove the vent for whatever reason then covering it is the next best option.
You can use heavy MDF or drywall to cover the air vent and ideally two layers of Green Glue (read my guide here) would be even better. You can then use acoustical caulk to seal any layers between the existing wall and the new layer of drywall or MDF.
The primary way sounds transfer from air vents is through unsealed gaps. By adding MDF or drywall you are blocking these gaps, which should greatly reduce or completely eliminate the sounds coming from air vents.
There is a downside to this option though; covering the air vent will make the room pretty warm during the summer months, which isn’t ideal for some people. If you require cross ventilation then perhaps an alternative method is best for you. However, if you have air conditioning installed, or perhaps even a fan or window, this isn’t much of an issue.
3. Upgrade the HVAC system
If your HVAC system is old then it’s probably pretty noisy, either because it’s using old, clunky technology, or it has worn out over time. Sometimes it can cause vibrations that are amplified by the open space in the vent.
If your HVAC system is old then you might want to consider upgrading to a newer, more modern HVAC system. Modern systems use quieter technology, which will result in less sound coming from the vent.
The added benefit of modern HVAC systems is that they are also more energy-efficient, saving you money on utility bills! If your HVAC system isn’t that old then you may want to consider the options below.
4. Install duct liners
If you don’t want to upgrade the system, or if there’s nothing wrong (apart from the noise) with your current HVAC system, then installing duct liners can be a very cheap and easy method of insulating sound. Duct liners have an insulation material that will absorb the sound that’s vibrating through the air vent’s inner walls.
Duct liners are fixed to the inside walls of the air vent and have a double sided liner. This is to prevent the liner from blowing glass wool fibers into the room when the air is flowing.
A cheap and effective duct liner that I’d personally recommend is Reflectix (see it on Amazon). You can order it from Amazon and typically it costs less than 30 dollars for a 25-foot roll, which should be enough to cover most air vent ducts.
5. Install flexible ducts
Because a flexible duct is bendy it can reduce the amount of sound that leaks from the air vent. Despite them being useful for soundproofing, they should only be used when absolutely necessary.
The way flexible ducts work in reducing sound is by creating bends in the duct. This makes it much harder for sound to travel when the air is flowing, due to the sound being partially absorbed every time it hits a bend.
The downside of using flexible ducts is that they can have small breaks in them, which then leak sound and reduce how effective they are in soundproofing. This is why they should only be used when absolutely necessary, ideally in places that are quieter so that sound doesn’t enter the duct and travel.
In order to mitigate this problem it’s essential to use a high quality flex duct, such as the ones from Dundas Jafine(take a look at Amazon for the pricing). This will reduce the chance of running into this problem.
6. Install soffits
The only way to soundproof air vents and ducts that are directly exposed to sound will be by installing sound insulating soffits.
For use in soundproofing, a typical soffit would be made from MDF with a layer of insulation inside. These types of soffits are very commonly used in home theater installations as they are very effective in reducing sound.
Some home theater enthusiasts will even go as far as adding layers of drywall with Green Glue (viscoelastic damping) in between the soffits. This is very effective but is only really necessary for rooms that require a high level of soundproofing.
Putting a flexible duct inside the soffit will create a lot of bends, which will provide an even higher level of soundproofing for the air vent.
7. Create a sound baffle
Creating a sound baffle is another good method of soundproofing an air vent. A baffle usually consists of a box that forces sounds to travel a longer distance, thus absorbing and reducing the sound along the way.
You can think of a baffle as a maze that has soundproofing materials, such as foam, along the inside walls. As the sound is forced to travel along a convoluted path, the vibrations are absorbed by the material, greatly reducing noise. This is somewhat similar to how mufflers work on cars to reduce the loud sound coming from the engine.
From personal experience I found creating baffles to be a very effective method of soundproofing vents. For even better results you can run a flexible duct along the crooked path, then seal the box off. This will provide about as much soundproofing for the vent as you’re going to ever get!
Please note that baffles are only effective for vents that have an HVAC system. This is because the ducts are much longer, so the sound can be reduced as it travels along the route. Using a baffle on a normal air vent won’t be very effective, as there’s barely any distance for the sound to travel, which reduces sound absorption.
8. Get professional help
Sometimes it’s best to call in the professionals. If you don’t fancy trying any of these methods, or if the size and length of the duct are going to need some major modifications to implement these methods, then getting professional help might be the best way forward.
A professional will be able to listen to any specific requirements you have and tell you which method will work best. It’s more expensive to hire somebody but at least you know the results will be exactly what you are looking for.
Summary of Soundproofing Air Vents
Ultimately there aren’t many quick solutions when it comes to soundproofing air vents, at least not if you want the soundproofing to be effective. This is true when soundproofing many things, including walls, doors, or other surfaces.
The information provided in this article isn’t just taken from my own experience, it also includes information I came across while I was researching how to soundproof air vents. A lot of the advice comes from soundproofing experts on Avsforum and various other platforms.
Soundproofing air vents can sometimes be fairly straightforward, or it can be a lot more complicated; it all depends on the layout you have. This is especially true for HVAC systems as there’s more to them than normal air vents. Before you even pick up any tools and get started, first work out where the main problem is coming from. If you don’t know where the problem is you’ll just be wasting your time and end up with bad results.
If you’re just dealing with a normal non-HVAC air vent then I would recommend just removing it or blocking it off completely. In some instances that won’t be possible, for example if you rent the property and the landlord doesn’t allow you to make modifications. You may also need ventilation in the room, so that’s something else to consider.
For HVAC vents you will get excellent results by following the information presented in this article. Don’t just take my word for it, some of the information in this article is compiled from what the experts on soundproofing recommend!
Take a look here at some of the insulation materials I recommend for soundproofing and acoustics.