A low whirring noise coming from the ductwork that connects your home’s HVAC system is to be expected. But, when this noise becomes amplified and distorted, it signifies that it requires looking into.
Learning about how to reduce the return air noise yourself can be very helpful. Some very basic maintenance work can fix most of the odd sounds that come from the return air ductwork. The main solution is to make sure that the system is clean enough for the air to pass through it.
You can also put some sound-absorbing materials into the ducts to reduce the noise. Let us go through the actual role of return air ducts in the larger system before understanding how to solve the problem with it.
Ventilation and the role of return air
In order to solve the problem, you will need to know what exactly you are dealing with.
Return air is the air that has made its tour across the room and now lost its thermic qualities. This air is now in the ducts on the way back to the HVAC system for additional conditioning.
It will be filtered and heated or cooled depending on what your AC unit is set on and after that, the air will join the ventilation system in the building traveling through the supply lines.
There are certain parts that you will want to familiarise yourself within the system:
- Return air vents can look fairly similar to the supply vents. When you put your hand over the grille if you feel a breeze entering the room that is the supply vent. However, if you feel a pulling sensation, then that is the return air vent
- Then there is the beginning of the duct system with a filter covering one wall behind the metal cover. The rest will be either exposed or covered with a thin layer of insulation. If the filter is popped off, you will be able to see the fan that pulls the air in and pushes it towards the destination
- Many systems also have AC coil that lowers the pressure inside the ductwork
What makes the return air vents so noisy?
Heightened pressure can be a potential cause of the noise that you will be dealing with inside the return air ducts. If the fans that are pulling the air in are not strong enough than the residence inside the ducts, the system will not work properly. Thus, we can easily say that any obstruction in the channels can impair the functioning of the ventilation system hugely.
A fully functional and open ventilation system produces a minimum level of noise like a very low hum that will be audible to only those who are sitting right next to the vent.
However, having to push past all the hurdles and obstructions will naturally result in noise.
If your system is having to work through a clogged grille that does not allow air to pass properly, a dirty filter, improperly installed ductwork, a lack of duct liner, or narrow ducts that cannot handle the volume of air they are processing, the sound levels will automatically increase. This is not only annoying but also hinders the longevity of the system.
Most of the solutions that help in reducing the noise are to make sure the vent is unobstructed but let us see all the various other methods we can also use to fix it.
How to reduce noise from return air?
- Open the vents
Open vents can cause your system to make noises. One close vent does not make much of a difference but two or three of these does make your system noisier.
Open your air vents as a first step if the noise from the return air in your home is getting unbearable. Next, check if the grill or vent is adjustable. If yes, switch to the most open position to ensure maximum airflow.
Check the vents regularly to ensure they are not closed. Vents that are close can put undue pressure on your HVAC and compromise its performance in the long run.
- Clean the air ducts/filters
After checking for open vents, if the noise still persists you may need to check the filter/ducts.
Air returns are sometimes covered by filters and ducts. Dust and other particles can get trapped in the filters as the air is sucked into the vents.
The trapped particles can cause clogging especially if the vents are installed in dusty rooms.
Clogged filters will make it very hard for the air to move, resulting in a noisy system.
Cleaning or changing the filters often say once every month is the only way to solve this problem. The filters are pretty cheap and changing them is very easy and hence does not require a professional. You can use a vacuum cleaner to suck the dust, cobwebs, and other debris and for a simple clean.
You can also remove the grille and give it a deeper clean. After that, vacuum the duct opening in case there is some obstruction that is clogging the system.
- Resolve ductwork issues
In some cases, a lot of air is forced to go through a small, limited space because of poorly installed or inefficient ductwork. This leads to a whistling or whooshing sound.
Correct the poor installation or make sure the ones that are in the proper position can handle the system. In the case of a more extensive system, you can get a professional to check it and make sure that the ductwork can handle the airflow.
Fiberglass duct liner is a sound-absorbent and hence, also a good alternative for your home and the noisy system. We can already tell air moving against metal is way louder than it moving through something more flexible. Hence, we can deduce that harder ducts tend to be noisier than their flexible counterparts.
However, the flexible ducts are prone to more bents and kinks which results in reduced airflow. Make sure that the flexible ducts are installed with optimal airflow in mind and if you choose to go for the hard ducts, choose the right size.
- Get the right grills and vents
Before proceeding to think about ways to reduce the noise from the return air, make sure that you have the right shapes and sizes of the grills and vents.
Ample opening is a necessary requirement for a good vent so that the air can enter very easily. They should not close too easily as that may lead to your system being overwhelmed.
Restrictive grills and vents not only produce unpleasant sound but also strain the cooling and heating systems and hence need to be corrected. You can get a professional to check and replace it. It may seem like a lot of work but your HVAC system will last longer.
- Install a duct liner
Typically, fiberglass duct liners are sold in big roles that cost a lot. Buying a full roll may not be a very practical and economical decision if you are looking to line a few vents. You can opt for a smaller piece of duct insulation or even use leftover automotive or home insulation.
- Measure and cut the pieces of insulation according to the dimensions of your duct wall.
- Properly clean and dry the walls so the liner can stick to them
- Apply spray adhesive both on the back of the liner as well as the metal wall
- Connect the pieces of the insulation to the duct wall once you’ve ensured that they are lined up properly
- The liner when pinned into the metal sheet after adhesion prevents to return air from sucking it up towards the filter
Sometimes you will require just half an inch-thick liner to prevent return air sound but you can always opt for thicker insulations to get better results.
- Reduce the static pressure
For some systems, there is always too much static pressure. This pressure is often the result of high volumes of air that get very difficult for the ducts to handle.
The solutions are different for every home but here are some of the available ones:
- Adjust the fan speed to a comfortable level with your HVAC system.
- Expanding the supply and returning plenums by adding ductwork. This will reduce the static pressure and hence make the system quieter
- Get a bypass duct if you have a single multiple-zone system. This will significantly reduce the static pressure
- Adding registers and increasing the grille size will increase the return air capacity
- Switching your present grilles and registers with high-velocity ones
- Upgrade and get a variable speed blower
If you are already considering replacing your HVAC system, this solution is appropriate for you.
A variable-speed blower will help in circulating the air more consistently around your house and there will be less air going through the ducts.
Variable speed blowers usually tend to operate at low speeds most of the time which means that they will barely make any noise but that depends on the heating and cooling demands.
- Resolve the central return problem
Usually, houses have one central return. The air handler or furnace is fitted next to the return plenum.
These types of systems can be pretty hard to be kept quiet as the blower motor is close and the small space does not allow installation of extra ductwork.
You can try to change the air handler installed right behind the bedroom wall to a more favorable location.
Read more posts from outdoor category: How To Soundproof An Apartment Door?
These are some of the easiest methods that can help you with the noise issue. If none of these methods works, you should get your system checked by a professional and see if any parts require replacement or repair.
If required, you may also have to go on the HVAC haul to get a new one.