Noisy Air Conditioner

Posted by AcousticalSurfaces on 06/20/2008 9:39 am | 5 Comments

Every spring, as soon as the weather starts to warm up we take more and more calls from people who are looking for the same thing – how to quiet a noisy air conditioning condenser. Especially in the early spring the noise from the condensers is troublesome because some people are running the AC while other people have their windows open. The constant drone of the machine can even be bothersome enough to drive neighbors to their breaking point.

Eliminating, or greatly reducing the amount of sound definitely possible, and really not all that difficult to accomplish, but it has to be done correctly – which is the intent of this little write up. Please keep in mind that all installations are going to require some site specific customization, but this should hopefully point you in the right direction.

For this example, I am going to use the condenser pictured below and explain what I am trying to illustrate.

Here is a list of things to consider:

1. The distance of the enclosure from the condenser.
2. The Height and number of walls.
3. What kind of wall, fence or enclosure to build – and who is building it?
4. Which product to use to line the enclosure?

Alright, where to begin? The first step that you need to take is to determine the recommended distance of a wall from the condenser. I would strongly recommend getting in contact with the manufacturer of your AC unit (with your make and model numbers) and tell them that you are going to install a privacy fence around the condenser and you want to know the recommended distance of the fence walls from the unit. If you can not get a hold of them for some reason, contact a local HVAC contractor. If that wall is too close to the condenser, you are most likely going to stress the unit and blow out the machine. I don’t want that to happen and neither do you – so take the time to get this part right!

Once you have determined the distance of the walls from the unit, it is time to figure out what kind of walls you are going to build, or have some else build. Both of the products that I will recommend below are going to need some kind of a structure or sub-rate to which they will be attached. Usually the most decorative and “fitting” fence is an alternating board privacy fence, or even a heavy lattice like this one that I found on the internet:

One you have decided on the distance of your privacy fence from the condenser and the type of fencing that you are going to use, it is time to decide the number of the walls you are going to build. If you are going to go through the trouble to construct walls, build three walls in the shape of a “C” if you were looking down at the unit. That was easy, wasn’t it? 🙂 I have always thought it would be a good idea to put the two side walls (the walls extending out from the house) on heavy duty hinges so they could be swung open in case someone needed to service the unit.

One of the harder questions to answer is the height of the walls that you are going to build. This is a little bit more of a difficult to answer because you have the exterior aesthetic of your yard to maintain. The overall height of the walls is going to be dictated by the height of the noise source. If we are using the picture above with the 3′ unit, the minimum height that I would want to see for a wall around the machine would be 4′-6″ tall – which is one-and-one-half the height of the noise source. Ideally, I would suggest installing a 6′ tall fence which is double the height of the noise source. With this in mind, the thing that is REALLY critical is eliminating the line-of-sight path. If you can still SEE the condenser, you are still going to be able to hear it. So if you are on a second or third floor and you can look over the walls of the enclosure you are most likely going to still hear a good amount of noise.

Alright, you are going to have to stick with me on this one, acoustic jargon beyond. When an air conditioner is installed next to a house or hard surface, sound that is going out of the back of the machine bounces off of the house and travels in the opposite direction. The house kind of acts like a spring board for the sound. So, if your neighbor has a condenser on the side of their house and you have a porch or patio on the side or back of your house and you can see the condenser, you are not only hearing the noise that is traveling from the machine to your ear, but you are also hearing the noise that is going out of the back of the machine, bouncing off the house and then making its way to your ear.

The red panel shown on the picture above is an exterior grade quilted fiberglass absorber. If it is at all possible, I would strongly recommend installing a panel like this one along the house – even with the top of the other walls that you built. This is going to greatly increase the effectiveness of the acoustical panel system as a whole – while adding a very minimal amount to the overall dollar amount spent for the project.

Finally, we are onto what products to use. For exterior installations, I really only have two options. The Sound Silencer panels and the BBC-EXT-TR2 Exterior Grade sound blanket. Both of these panels are very different and I will do my best to describe the each and listing the advantages and disadvantages of each.

The Sound Silencer panels come in 2′ x 4′ panels and either a 1″ or 2″ thickness. These are rigid boards made from a hollow, expanded polypropylene bead. If you are installing these panels, I would strongly recommend making the walls of your enclosure out of 3/4″ exterior grade plywood and sealing up all of the air gaps with a sealant. The plywood is going to act as a good noise barrier coupled with the sound silencer, but more as a structural element to support the panels than anything else. The panels can be installed onto the plywood with a construction grade adhesive or be screwed through and into the plywood. The Sound Silencer panels usually cost $5.50 per square foot for the 1″ and $7.50 per square foot for the 2″ panel. The acoustical data for the 1″ panel is NRC: .45/STC: 9 and the 2″ panel has an NRC: .70 and STC: 13. One important thing to keep in mind about the Sound Silencer panels is that if they are exposed to a large amount of sunlight, the polypropylene will start to break down over time.

This is a picture of the surface of the Sound Silencer panel. More information can be found by clicking HERE.

The BEST product that we have for this type of installation is the BBC-EXT-TR2 Exterior Grade sound blanket. These panels will block as well as absorb more sound than even the 2″ Sound Silencer, but they are more expensive. These panels are constructed by stitching a 2″ (nominal thickness) fiberglass layer to an 1/8″ thick, 1# p.s.f. Mass Loaded Vinyl noise barrier. The fiberglass is encapsulated in exterior grade vinyl – which is similar to that used for covers for a boat or cooking grill. We install grommets through the top, middle and bottom of the panels and sew an exterior grade vertical Velcro seam along the left and right of each to attach one panel to the one next to it. These panels are intended to be installed outside and last for years and years without breaking down or failing. The only time that I have seen a panel fail is where it was not installed tight enough and allowed to “whip” in the wind. The grommets pulled through the reinforced vinyl destroying the mounting point. We can use a few different colors of vinyl for the backing: (standard) Gray, Tan, Green or light blue. We can also use a few different colors for the quilting: (standard) Gray, tan or black.

The BBC-EXT panels are all custom built to whatever measurements and sizes needed – so they will line your enclosure perfectly. The vinyl backing is intended to be mounted to a chain link or alternating board style privacy fence. The fiberglass quilting should face the noise source and is very effective at absorbing the reflective noise within the enclosure. Both the vinyl and the fiberglass are important to the performance of the product. The vinyl blocks the sound and the fiberglass absorbs the sound. If one were to build a concrete enclosure the sound would bounce around in the enclosure and spill out over the top. Absorbing the sound with the enclosure GREATLY reduces sound leak over the walls. The cost of this option is going to depend on the quantity and size of the panels needed. I usually tell people to ballparkthe cost for the panels at about $18.00-$20.00 per square foot. The cost? has a direct relationship to the size of panels that you need. It is a more expensive option, but it truly is a situation where you get what you pay for.

This is a picture of a small sample of the BBC-EXT product. More information can be found by clicking HERE.

Below is a picture of a larger installation that was recently completed. I am waiting to hear back from the customer with his description of the performance of the panels. Here is part of an E-mail that he sent just after the installation was completed:

Ted,
…the fence was installed on Saturday morning. I have many pictures for you. I have to tell you that your product exceeded my expectations. Exceeded any expectation. In order to hear that compressor now, I have to wait until about 3am and then open the window in direct line of the machine and strain to hear just a distant buzz. It is safe to say that the fence is a tremendous success. I have been so stressed over this situation that I’m still afraid that for some strange reason that the fence will stop working.

Thanks, Carmen

If you have questions about the enclosure itself or the products suggested, let me know.

Additional Resources

Creating Better-Sounding Rooms

Download eBook

Solutions to Common Noise Problems

Download eBook

CAD, CSI, & Revit Library

Access Product Cad Files