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 acoustical 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 acoustical panels 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.
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
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
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!
Great post ! Building an enclosure works, and it’s pretty cheap. A simple frame made of 2×4 boards covered with 2′x4′ acoustic ceiling tiles (made for hanging grid ceilings) is a good start – put the “pretty” side of each panel toward the compressor – and don’t forget the floor and top of the box. Two layers would be twice as good (be sure to stagger the joints to keep sound inside).
Read your article, I learn a lot. thank you for sharing.
Ted, I enjoyed reading your article. I replaced my entire home AC system and added a zone about 12 years ago, and they are damn noisy. The biggest problem is the vibration of the metal grills that cover the top of the units and hold the fans. The touch the metal sides of the condenser units and REALLY add to the noise. If I place my hands on the grill and push down the vibration stops and all you hear is the fan, which isn’t too bad. So…..I want to place some type of vibration reducing washers on the screws that hold the grills, or a gasket where the grills touch the condenser, but not sure if there is good material that someone has used before that won’t wear out quickly. BUT, there might be an even better solution that I haven’t heard of. I had a tech out here but he just said to stuff some rubber under the grills and that doesn’t work. Any ideas?
Franco,
Good morning and thank you for the post. Have you looked into the HG Washer bushings? They may work:
http://www.acousticalsurfaces.com/mounts_springs/neoprene_isolators_hg.htm?d=24
-Ted
Ted, we recently moved into an apartment with an electric, water based heating and cooling unit (i.e. heat pump). It’s located in a closet in our living area, and while it works very well, it is very noisy. The closet has a luver door, which I assume is necessary for ventilation. I’d love to line the inside of the door to block the noise, but several people have advised me against it. What can you recommend to deal with the noise problem? Do you know of anyone in the Philadelphia area I could ask to take a look at my situation? Thanks for your help.
Neal,
I would assume that the louvered door is necessary to keep the machine from overheating as most louvered doors are installed for this reason. From an acoustical standpoint, there is not a door separating you from the noise source. I would strongly consult a local HVAC service tech to advise you what you can and cannot do.
You may get some reduction by installing an absorptive surface on the side and rear walls of the closet as often times what happens in situations like this is that ALL of the noise being generated by the machine reflects off of the walls and comes out of the door. This scenario is much like a band-shell where all of the sound pressure only has one direction to go. Many people use the 1” or 2” Echo Eliminator (http://www.acousticalsurfaces.com/echo_eliminator/wall_panel.htm?d=0) on the walls of the closet to reduce this. These panels are very cost effective and do a really good job at absorbing sound.
Thank you,
-Ted
Thanks Ted; that’s what I thought you would suggest. I’ll give it a try.
Keep your fingers crossed for me!
Neal
I live in a 2nd-floor back unit in a big apartment building in NYC. On the back of the adjacent building, about 15 yards away, there are two machines — one old and one newly-installed — that are keeping me up at night. The old one goes on and off all the time, including the winter, and when it starts up, it makes kind of a “boing” sound & runs maybe 10 minutes at a time. I can’t see this machine to be able to describe it. What type of machine do you think this is? I can live with it, but it’s annoying. The second, newly-installed machine I’m having trouble tolerating. It has been running from 3:30am to 7am every morning, is a large vented thing and connects to a tube that runs around their building where I can’t see it. What kind of machine do you think this is? Do you have suggestions I can convey to our superintendent who can then convey them to the neighboring building? The machines and my apt unit are basically on the bottom of a narrow cement and brick canyon. Both buildings are 15 stories.
Hi Katie,
Thanks for the question. Unfortunately, you will probably not like my answer.
We can build custom noise barriers around these type of machines. I am not aware of what that specific machine is from your description. The problem with this solution that they are custom made and very expensive.
I would suggest going to your city or superintendent and see if they will conduct a noise study and hopefully have them pay for the solution if it is bad enough.
Thanks,
Ted
Hi Ted/ Tyler
This is just the kind of info I have been looking for. I live in England where this is generally not such a problem, so not much info from UK sites. However, I recently had installed a Hitachi system which will be an aircon system in summer (assuming we get any warm weather then) but is also a heat pump working to heat the house in winter. And it is very efficient, produces a lot of heat for little power input and is very quiet inside our rooms. BUT, the outdoor unit can be really noisy when it is producing max output and the outside temp is down to freezing. It sounds like a small airplane! We can hardly hear it, but our neighbors are finding it a nuisance at night. I am also concerned about what it will sound like in summer if we get a hot spell and people have windows open. The unit is on our wall and quite close to their boundary. My neighbor is happy to help me find a solution. The only problem seems to be, is it practicable to import acoustic panels or blanket from the USA? Or is there a UK agent for your product, or anything similar?
Thanks for the comment! It’s great to hear that people still find these articles helpful.
I would start by consulting with a local service person – someone who would come out to repair the machine in the event it was not working. Talk to them about your plans to build a wooden fence around the machine. Ask them how much room around the machine it will need to operate and if you will need to make any of the walls of the fence removable so that it can be serviced. Once that is determined, you can either build, or have a local company build a wooden fence around the machine outside. Depending on the type of fence that is built, this may or may not stop enough sound to make your neighbor more comfortable.
If the fence itself is not enough, we will want to proceed with that on a per-job basis. I will likely need you to send me a few digital pictures of the area as well as the measurements (width and height) of the walls of the fence. I have even used Google Earth in the past to get satellite pictures of the buildings so that I have an even better idea of the area, distance, details, etc. In the event that the fence does not help to the degree needed, we would either need to fabricate a set of exterior-rated blankets and send them to you, or potentially help you try to source something locally.
Thanks,
Ted
I found this article very helpful. Fiance and I just moved into a BEAUTIFUL, brand new green building in Brooklyn and we have a huge terrace with a view overlooking Manhattan. Summer is coming so I was excited to host some get-togethers out there, only problem is the SUPER noisy ac/heat air compressor or something. I don’t want to build anything too expensive or permanent because it is a rental plus, it is a NYC iniative of Middle Income Housing so any changes to the property would need to presented before a board. My estimate in measurements is 3ft in Length x 2ft in width x 2.5ft in height. Any suggestions? Please email me so we can discuss estimates in the blanket you mentioned? [email removed for privacy]
Jennifer,
Very glad to hear you found this helpful. Sorry to hear about the problem you are experiencing on the terrace. You provided some measurements, but you did not explain what it was you were measuring.
If you can SEE the air compressor, you will be able to hear it. Because of this, your noise barrier will need to introduce a line-of-sight-barrier between you and the noise source. You could use exterior-grade plywood to build a cost-effective and free standing wall that might help. The products that we have to offer for outdoor use are usually in the $14-16/sq. ft. range, depending on the product, dimensions, and options.
Thanks,
Ted