Air vents are probably one of the largest sources of noise transmission in a house since they connect different rooms without any sort of insulation within them.
In this article, I will go over how to soundproof a vent, be it by completely sealing it off and preventing airflow, or by installing sound-absorbing materials in it to absorb some of the soundwave energy.
So, without any further ado, let’s get started!
Table of Contents
Difference between soundproofing and sound absorption
First and foremost, learning the differences between soundproofing and sound absorption is really important since people tend to think of them as being the same thing, but they are definite not:
Soundproofing consists of blocking the path where sound could get in or out, lowering the overall noise that’s allowed to get through a wall, for example, and the best type of material for doing this is one that blocks sound instead of just absorbing it, such as drywall, mass loaded vinyl, etc.
Sound absorption, on the other hand, consists of using materials that have a lot of air pockets in them, and that are dense and thick. This kind of material absorbs a lot of the soundwave’s energy and makes it die out quicker.
Of course, when soundproofing, a combination of the two generally gives the best results, such as putting rockwool inside of an interior wall and covering both sides with drywall.
With air vents, it’s not as simple as with walls, but more on this is just a second.
Different Noise Types (Airborne and Structure-borne)
Airborne and structure-borne noises are two completely different things and should be treated differently:
Airborne noise is the one that travels through the air, such as voices, television noise, etc. Those soundwaves travel through the air until they hit an object (a wall for example) and transmit those vibrations through the wall into the space beyond it (another room, for example).
Structure-borne noises, on the other hand, occur because of the impact of an object with a structural element of the house, such as footsteps on the floor above you or on the stairs. That impact that occurs transmits the vibrations through the structures of the house and is then perceived as sound.
Sadly, air vents are extremely susceptible to both kinds of noises because they are, essentially, a large empty space made out of metal where sound can easily travel through and that doesn’t absorb any impact or structure-borne noise. In fact, one could even consider it as an amplifier of impact noise.
Now, what can we do about it? Is there any way to completely remove-, or to at least lower the transmission of noise in an air vent?
Can you Soundproof an Air Vent without preventing airflow?
Sound can get through the tiniest of gaps, just like air, and completely soundproofing an air vent without blocking it is impossible because the airflow would be lost. Installing sound-dampening and sound-absorption materials will help absorb some of the noise in the vent, but may also restrict airflow.
It all depends on your priorities: If a lot of noise is coming in through the vent and you absolutely want that noise gone, then you could seal off the air vent entirely. Just know that doing this means that the HVAC system will no longer be able to heat or cool the room where the vent was sealed.
How to Soundproof an Air Vent
Here I will be listing the options you have for soundproofing an air vent, be it by completely blocking it off if you don’t care about losing the airflow fir heating & cooling, or by simply dampening the sound and not letting as much get through the vent to where you are.
Seal it off completely (no sound or air/heat will get through)
Like I mentioned, sealing off a vent entirely will prevent sound as well as airflow from getting through. So, keep that in mind since you won’t be able to use the HVAC to control the temperature in that specific room if you decide to go this route.
Spray Foam method
Spray foam is probably the easiest and most effective method of sealing of an air vent because it’s easy to apply and expands a lot, covering a lot of surface really quickly and without leaving any unwanted airgaps.
It’s worth noting that a single can of spray foam may not be enough depending on the size of the vent, so make sure to get at least a couple. It’s also really easy to get; just go to your local hardware store or buy this one from Amazon.
When applying it, make sure that it covers the entirety of the vent, and be careful not to do it too close to the vent’s opening since it might drip or expand outwards, in which case you would need to let it dry completely and cut the excess off with a knife.
Important note: Spray foam, even though it’s got fire-retardant chemicals in it, is still considered quite flammable, so keep that in mind.
You could also combine spray foam with the next method for even better results:
Drywall (plus other materials)
Drywall is an excellent sound and heat barrier, especially the one that has fiberglass in it (generally, all 5/8” drywall has fiberglass) since these fibers help absorbing sound even further.
Using a block of drywall to completely seal the air vent will lower the amount of noise drastically, and if you use it in combination with spray foam, or any of the methods I’m going to be listing in the next section (acoustic foam, rockwool, fiberglass, etc.), all the better.
Putting a piece of drywall on your existing wall won’t look that pretty though, since it will protrude a bit. I’d recommend cutting the drywall to the exact measurements of the vent and pressing it in. Then, using acoustic caulk, you seal all around it so that no air can leak through the vent.
After this, you can sand everything and paint over it and no one will even know that there’s a vent there.
Install a magnetic vent cover (easiest solution of all)
Although this might not be my first choice, at least in terms of noise reduction, you can definitely get vent covers that are thick and solid, not louvered, and that are magnetic, allowing you to put them on top of the already existing vent without the need of any additional tools, spray foam, sealants, etc.
The only issue is that these covers generally will have a couple spots that are not 100% sealed off unless you install them properly and, therefore, sound and air may be able to get through. But overall, they will reduce the transmission of noise.
You can get them in different sizes and colors and they aren’t that expensive.
Partially seal it off (Not as effective, but heating/cooling the room is still possible)
Image: Acoustical Surfaces.
If you still want to get the benefits of an HVAC system but still want to reduce the noise that’s being transmitted through the vents, then the following steps might help.
Note: Most methods that reduce noise will also somewhat hinder airflow and, therefore, heating or cooling through the vent won’t be as efficient.
Fill the entire vent with a sound absorbing material
Sticking a large piece of dense foam into the vent and making sure that it fits snuggly so that there are no open gaps left will drastically reduce the amount of noise that is able to get through while still allowing for airflow, although it’s worth mentioning that airflow will be lower than before, making heating & cooling much less efficient.
For this, the only type of foam that would work is regular acoustic foam, but make sure to get a huge chunk of it since the thicker & denser, the better.
Note: Acoustic foam blocks aren’t as widely available as foam panels, but they will allow you to cover the entirety of the vent, reducing noise by quite a bit. You can get blocks like these and if they don’t fit perfectly, simply cut them to the required size (always a bit larger so that once you insert them into the vent they press against the sides), and that’s it.
Make a sound absorbing maze inside the vent
Sound likes travelling in a straight line, as soon as you build a maze out of sound absorbing materials, like acoustic foam, for it to navigate before it can reach the room, the level of noise that ends up getting in will be drastically lower.
It should look something like this;
Now, this method does help absorb some of the noise without hindering airflow in any way, but it’s not going to reduce the noise as drastically as some of the other methods.
Adhere acoustic foam to the inner walls of the vent
This one is pretty self-explanatory; Using self-adhesive acoustic foam panels and adhering them to the inside of the vent, covering as much surface as possible, will absorb some of the airborne sound as well as some of the vibrations in the vent itself.
This method will only be effective if you’re able to install the foam quite deep into the vent, since just covering 30cm with it won’t do much.
Install Rockwool Ductslabs
This is a product made out of rockwool and sold specifically for air vent insulation. Rockwool is excellent at absorbing sound and it’s also a good thermal insulator, making your home more energy-efficient since it will prevent heat loss.
Of course, you can buy any rockwool that has an aluminum backing and install it in your vent, and just like I mentioned with the acoustic foam panels, make sure to cover as much surface as possible for better results.
One last pro about rockwool is that it’s non-flammable and will never help spread a fire, which is not the case with acoustic foam.
Important note: The thicker the rockwool, the better, since it will absorb a lot more energy. And this also applies to acoustic foam.
Learn more about soundproofing materials and if they are flammable or not.
Consider a Fiberglass Duct Liner
Fiberglass internal duct liner is commonly used in many commercial heating, ventilation, and air conditioning (HVAC) system. Fiberglass duct liner provides sound attenuation by dampening noise from HVAC equipment, and sound from adjacent office spaces. Fiberglass duct liner provides thermal insulation for air ducts, preventing the air ducts from losing expensive conditioned air.
The problem arises when the black gritty coating on the surface of the duct liner which locks down the fiberglass fibers starts to deteriorate and those fibers get blown into the room which, if inhaled, could cause irritation of the skin, eyes, and respiratory system.
Essentially, fiberglass duct liners can be used but you should keep an eye on them and repair/replace them when necessary, which is why I’d highly recommend going for rockwool.
Note: If you want to completely seal off the vent, then you could get a lot of fiberglass or rockwool, stuff it into the vent and then seal it off with drywall. The rockwool/fiberglass will absorb a lot of the noise and the drywall will serve as a barrier.
Pros of Soundproofing an Air Vent
- Noise reduction.
- Better thermal insulation as well since heat can get out through the vent when the HVAC is not working (vents are generally made out of thin sheets of metal and conduct heat with ease).
Cons of Soundproofing an Air Vent
- Sealing off the vent prevents airflow and, therefore, you won’t be able to control the temperature inside the room with the HVAC.
- Depending on what method you choose, unsealing it can be a lot of work.
What methods/materials to avoid when soundproofing Air Vents?
Although fiberglass tends to be used to reduce the noise coming from a vent, it’s not a safe material to use since the small glass particles can irritate your skin, eyes, and respiratory system, which is why I would recommend you go with rockwool if you’re going to be lining the walls of the vent with a sound absorption material.
On that same note, acoustic foam and spray foam are quite flammable and, in case of a fire, will actually spread the fire to other structures, which is not the case with fiberglass and rockwool.
So, in short; Rockwool is your safest bet.
Conclusion
Soundproofing a vent can be a bit tricky, especially since you want the vent to actually be functional.
The simplest way is to completely seal it off if you don’t care about the vent itself. However, if you don’t want to seal it off entirely, then you should understand that 100% soundproofing it won’t be possible and that some noise will still be able to get through.
Still, you can definitely absorb a lot of the sound in the vent itself by installing Rockwool Ductslabs, or simply adhering a lot of foam to the interior of the vent.
Last Updated on May 10, 2022 by Facundo
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