How to Quiet Noisy A/C Compressor
Please keep in mind this is my quick Photoshop sketch simply to illustrate the theory explained below.
As the weather heats up, and summer gets into full swing, we are getting more and more calls as well as E-mails about air conditioning compressors bothering home owners as well as neighbors. The problem can be fixed fairly easily and inexpensively, but either way, it needs to be done correctly. In some cases, doing ALL of the things that I will discuss below are not possible, so you have to do the best you can with the limitations of your situation. If you have questions, please feel free to contact me to discuss the particulars of your problem. Often times digital pictures of your area are a great help.
Here in the Midwest, air conditioning units are installed outside on ground level, somewhere near the house – and most often, on the side of a house that is near a neighbor. When the air conditioning turns on, the compressor outside comes alive, which generates a fair amount of mechanical noise. Whether the exterior of the house has siding, concrete, wood, or stucco, the sound tends to bounce off the house and usually heads directly toward neighboring windows.
To fix this problem, you are going to need to build an “enclosure” around the unit. This will require a bit of construction on your part, and there are a few things to consider – acoustical performance, not inhibiting the operation of your system and aesthetics.
The first thing to consider is the location of the walls of your enclosure – which is the most critical aspect of approaching this situation. Now, I’m not an HVAC Contractor, so please forgive me if I am not exactly correct here… The purpose of the compressor outside of your house is to cool and compress the Freon in the AC lines. This is why the large volume of air coming out of the top of the unit is warm. If that airflow is inhibited, you can seriously damage your HVAC system. The compressor needs a certain distance around (and over) it to allow the system to operate correctly and for servicing the unit – so if you have any questions, please contact a local HVAC contractor for advice.
Let’s talk about the walls of your enclosure…
The first two things to think about – from an acoustical standpoint are that you need to eliminate the “line-of-sight” sound travel. No matter what kind of acoustically absorbent or “sound proof” product you line an enclosure with, if you can still SEE the unit, you have not chosen the most efficient approach. I understand that sometimes this is not possible, but I wanted to point out that it is definitely ideal. If you are considering building walls only (i.e. no roof) I would suggest a wall height that is double the height of the noise source. For instance, if your AC unit is two-feet tall, your wall height should be four-feet. If that is not possible, which often times it isn’t, the higher the better. If you need a shorter overall enclosure, I would suggest making an angled roof over at least part of the compressor. If you can imagine the top of a back-stop for a baseball field, that is the type of overhang I am talking about.
The acoustical treatment…
We have two different products that can be used outdoors to treat the inside of the enclosure – both of which need some kind of substrate to attach to. The most common lining for the air conditioning enclosure is the Sound Silencer panels. These panels come in a 1″ and 2″ thickness, and are sold in 2′ x 4′ panels. The 1″ thickness normally sells for about $5.50 per square foot, or $44.00 per panel, and the 2″ thickness sells for about $7.50 per square foot, or $60.00 per panel. They can be cut with a table saw or skill saw. Cutting the 2″ panel can get just a little tricky, so please call to discuss the installation details. This panel is going to need a sheet of plywood to attach to – and can attach with a construction grade adhesive (PSA-29) or simply with screws and washers. The 2″ Sound Silencer panel is rated with an STC of 13, and an NRC of .70.
There is one quality of the Sound Silencer panel that you need to consider when thinking about using this product. We have found recently that with prolonged ultra violate exposure; the polypropylene core of the panel starts to break down. This happened MUCH, MUCH faster with the white, so for exterior applications, ONLY use the charcoal color. The charcoal dye acts like window tint, protecting the polypropylene from the sun. If the area is shaded for most of the day, or if the panel has a roof, you will be fine with this product. It is going to be the most effective when backed with a solid board of plywood, rather than spanning gaps in a privacy-style fence.
Another, and more costly lining is our Exterior Grade Sound Blanket. This product is commonly used on chain-link or privacy style fences. This panel is constructed by quilting a nominally 1″ or 2″ thick layer of light density fiberglass to a 1/8″ thick, Gray, reinforced layer of mass loaded vinyl. We make these panels specifically to the sizes needed on a per-job basis. Our most common application for this product is around large air-handlers for commercial applications simply because these machines normally have chain-link fences around them. When we fabricate these panels, we will pound grommets through the top, middle and bottom of each, and line the vertical seams with an exterior grade Velcro to attach one panel to the one next to it. Because these panels are made on a per-job basis, I would rather provide a quote based on your measurements than on a ballpark price, but if you would like some idea, the cost usually falls in the $14.00 per square foot neighborhood.
The Exterior Grade Sound Blanket solution will out perform the Sound Silencer panels in most instances simply from an acoustical standpoint – but the applications are not normally an apples-to-apples comparison. The Quilted Curtain panels have an STC of 27 and an NRC (with the 2″ facing) of .85.
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I seriously enjoyed this article. This is not some spam BS. I own a heating and cooling company in Chicago and we have been getting a lot of inquiries about sound from ac condensing units and what to do about it. After being in the business for over 40 years it didn’t really occur to me to build a absorber wall for the unit. We have used compressor blankets that the mfg’s provide and the results are poor at best. I was out at the Goodman mfg plant in Houston Texas where I was able to take a tour which included their sound testing lab. It was impressive and used some very sensitive equipment to measure db’s and frequencies. It seems that after seeing that I realized a bit more about the way the vibrations travel and the blankets can only do so much. I will without a doubt offer this as a possible solution to this menacing problem. thanks for the tip. I would like to know if I may use this info on my website?
Mitchell Moore
Citywide Supply & Service
Chicago AC Repair
What about interior “whooshing” sounds coming from the interior vents and dealing with people with hypersensitive hearing and consider the loud rush of air coming out of the vents an annoyance?
any ideas on how to difuse the noise?
Eric,
Quieting air flow is a much different approach than a noisy machine. To eliminate the air flow noise, either a soft duct lining needs to be installed into the duct or a duct silencer needs to be installed in-line with the duct system (like a large car muffler). Both are VERY difficult to try to get into a retro-fit situation. Is this a residential situation you are considering?
What about units that are on the roof? This is a condo building and the folks under me have their unit on the roof and I get to hear it thumping on and off
all night.
They claim it’s been checked and working properly…maybe so but the noise
is unpleasant.
Would this type of sound proofing work for roof AC units?
We live in CA.
I have noticed that on new units, one next door & one at a friends house, that the compressors are now being wrapped with some type of weather proof insulation much like the ones you can place around a water heater tank.. On both these units the humm is completely gone and you only hear the fan. My question is can you put one of these on a unit that is 5 years old to help quiet it down some. Thanks Forrest Mixon
Kay,
Thanks for your question. Ted, our normal blog writer, is out so I am replying in his place.
I don’t believe the Quilted Curtains would help your particular situation. You see to have a vibration problem instead of an airborne noise problem. I would recommend isolating the unit from the roof so that it is not in direct contact with it. This will make it so that the vibrations the unit is creating cannot travel into your living space.
To help reduce the vibrations, we do offer many different options, depending on the details of your specific situation. Feel free to give me a call and I would be happy to talk with you about your options.
Tyler Moynihan
Phone: 952-466-8233
Email: tyler@acousticalsurfaces.com
Forrest,
Thanks for your question.
Unfortunately, I cannot answer that question. That really is a question for the manufacturer of the AC Unit. The specifications of the AC Unit determine the treatment that you can put on or around them. Again, this is not my industry, but the manufacturer will be able to recommend what you can do.
If you have any other questions, let me know.
Tyler Moynihan
Phone: 952-466-8233
Email: tyler@acousticalsurfaces.com
Tyler,
What if the noise problem isn’t on the outside of the house, but on the inside? Our furnace/air conditioner combo makes a lot of noise when it blows; is there anything we can do to minimize it?
Hi.. I live in an apartment on the top (fourth) floor and the condensers are above my unit. There are four floors and four condensers above my bedroom supporting each apartment. I am on the fourth floor. The noise impedes my ability to sleep. So I have been trying to discuss ways to muffle the sound with the maintenance crew. Any suggestions would be greatly appreciated. Thanks…
icehead,
There are a few things that you may be able to do to quiet down the system. I would probably suggest first calling an HVAC contractor to check out the system to make sure it is functioning properly. If it is, there are really only two other approaches. The first is to have a custom made in-line duct silencer fabricated and installed. These are basically like a big car-muffler for the system. It forces air past a duct lined and baffled with an acoustical absorber. Each unit is custom made based on the height, width, length and CFM (measure of airflow) associated with the duct. The other option is to line the inside of the duct with something like the Quiet Liner (http://www.acousticalsurfaces.com/quiet_liner/quiet_liner.htm?d=26) which is a recycled cotton roll that glues to the walls of the duct.
Please let me know what additional questions you have.
Thank you!
-Ted
Dawna,
Sorry to hear that you’re having problems with your living situation. Just about EVERY time a similar problem is expressed to me, the only way to start to reduce the sound that is bothering you is to put each compressor (or the lot) on some kind of spring isolator which can significantly limit the amount of vibration energy that is currently getting into the structure. Typically these machines are not overly loud but because of the nature of the machine, they can introduce a massive amount of vibration energy that will transmit itself down, through the roof, joists and physically move/shake your apartment.
There are quite a few different models and types of spring isolators but in most cases, one of the Type C Spring mounts are used: http://www.acousticalsurfaces.com/mounts_springs/spring_isolators_c_cip_ciw.htm?d=24 so that the machines do not fall off of the isolators.
Please let me know what additional questions you have!
-Ted
Ted…can you offer some thoughts on hanging the acoustifence on the enclosure surrounding ac units. The 6 ft x 30 ft size is perfect for my dimensions. Thank you for your info!