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Old 07-02-2020, 09:19 PM   #1
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QUIET Self-Contained Air Conditioner

Currently have a 17 yr. old 110V 16,000 BTU self-contained AC unit under the settee in my salon. It's very noisy - about 70 dB just outside the cabinet and 55+ dB elsewhere in the salon. Time to replace it but would really like to get something significantly quieter.

I've been pointed toward a Dometic model # DTG16-1171-410A 7MR
https://www.dometic.com/en-us/us/pro...o-dtu-_-115228

This unit is billed as bering quiet but no specs are available to quantify what that means. There is an optional sound cover that supposedly decreases the std. noise level by 3 to 5 dB but that doesn't seem all that impressive.

Might anyone have experience with this Dometic model or perhaps recommend some other self-contained AC system?
Thx -
Jim
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Old 07-02-2020, 09:28 PM   #2
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I put new Dometic models on my previous boat. It was a definite improvement as far as noise goes. Also realize and do some research on what a decibel is. It is an exponential increase(or decrease) in noise. So 5db could be quite significant!
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Old 07-02-2020, 09:50 PM   #3
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I think MarineAir bought out Dometic??
The less than 16K reverse cycle A/C are about the same.
I cannot tell if my 3 year old MarineAir are any quieter because I should be wearing hearing aids. My company have yet to complain about the noise.
I did put a soft start on the 16K unit. The 12K is factory stock.
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Old 07-02-2020, 09:57 PM   #4
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Thx - is the soft start necessary if I don't have a genset?
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Old 07-02-2020, 10:02 PM   #5
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I think MarineAir bought out Dometic??
I think it is the other way around....
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Old 07-03-2020, 03:44 AM   #6
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I think it is the other way around....
That sounds about right. I can't keep track of how many good, "individual" companies I've called in the past few years only to hear the phone newly answered something like "Welcome to Dometic" (cue sinking feeling).
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Old 07-03-2020, 04:34 AM   #7
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I replaced an 8 year old Marine Air 16k with a new Dometic 16k. The noise sounds the same to me.

I put a Marine Air/Dometic sound shield on another unit. A phone app did indeed measure about a 5 dB decrease. However, dB being a logarithmic scale as noted, it was a small improvement. (3 dB is about the limit of a perceptible change in sound level.) It covers the compressor to reduce that particular noise but the fan is about as loud.
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Old 07-03-2020, 04:43 AM   #8
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I have this 12,000 BTU Dometic model in my 33' boat. My boat did not originally come with it from the factory...I had installed as an after-market add-on. I purchased the unit via the factory so I knew it was the exact same model they used and so I didn't have to figure out all the necessary ducting components, grills, bits, etc. that I needed.

Having been on other boats in this size-class with A/C, I thought my new Dometic unit was reasonably "quiet" in comparison. While the installer fastened the a/c unit's feet to the boat using rubber grommets to help dampen vibration, I still wanted better. I found, on-line the "optional compressor cover" and installed it (quite a bit of work and cutting for me). It helped a lot, but I wanted better still. Note that the text on this cover says "reduces the COMPRESSOR noise by 50%". While it may do exactly this (i.e. reduce COMPRESSOR noise by 50%), it does not reduce the overall a/c noise by 50%. It seems the main noise culprit is not the a/c unit itself, but rather, the vibration & echo it can cause. If it’s installed under/behind cabinetry, for example, the vibration can be amplified. If you think about it, it’s not much different than the physics and operation of a sub-woofer speaker. Vibration is THE enemy.

While I don’t have any before & after db numbers to share here, I can tell you that my efforts did make a BIG difference. On my boat, this unit is installed under a storage cabinet just on the outside of my forward stateroom wall. If we want to sleep at night with the a/c on, it’s no problem. Yes, you can hear the humming of the a/c, but it’s not objectionable.

You mention that your old unit is 16,000 BTU and the link you give to the new unit refers to 12,000 BTU (with 16,000 available). My only comment here is that, if I had to do this project over on my boat, I would seriously consider the 16,000 BTU unit, space & power permitting. 12,000 BTU has been just fine for 99% of my cruising in northern Europe in the summers, Now, however, I use my boat in the Mediterranean and 12,000 BTU helps – but it is not really enough.


So, in summary, I strongly recommend the following:
1) Make sure to use some sort of rubberized mounting grommets to try to prevent transmission of vibration to the boat structure
2) Install the optional compressor sound cover at the same time you install the a/c system, as it takes a fair amount of extra space and it might be more difficult to get it on later
3) Line the "plenum" area that encloses a/c unit with 1"++ foil-backed engine room insulation. Tape joints. No cracks!
4) Check all screws in surrounding cabinetry/joinery (if any) for tightness. Consider adding a very thin layer of rubber between any bits of wood that are screwed together and making noise.
5) Avoid any sharp turns in the output ducting
6) Make sure no engine room air can get sucked into the a/c unit return-air “plenum”. (risk of unpleasant odors being quickly distributed throughout the boat)
7) Absolutely DO get the smart start, unless you have an inverter system with a power-assist feature. While the power draw of these units is very reasonable when running, the heavy starting load can be the thing that will have you forever stepping ashore to re-set circuit breakers.
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Old 07-03-2020, 06:31 AM   #9
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Wow - you sound as crazy as I am about sounds!
Thx for the GREAT suggestions!
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Old 07-03-2020, 07:08 AM   #10
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One of the things to understand about new AC units is that there is a wear in time on blowers and compressors. Simply, they get quieter as bearing surfaces wear in. I've seen this on home central AC units and the Webasto units I bought in 2015.

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Old 07-03-2020, 07:11 AM   #11
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My old unit makes a racket! If you get used to it you can sleep through it cycling. I would replace it but it works perfectly.

If it aint broke, don't fix it. KISS (keep it simple sailer)

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Old 07-03-2020, 07:13 AM   #12
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Both RV and marine air units suffer from direct fan and air flow noise.

If the intake, or exhaust is close to registers...lots of noise....only ducting or mufflers will really help.


Nowadays the actual unit noise isn't bad for mist of them.
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Old 07-03-2020, 07:19 AM   #13
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Marine Airrrrr self-contained units in the early 2000's were often named Vector Compact, and we had two 16K BTU VCs.... that gradually got noisier over time.

Marine Airrrr introduced the Vector Turbo, said to be quieter, more powerful (than a speeding locomotive?), better air handling, more easily configurable, and with a composite drain pan.

Dometic bought Marine Airrrrr.

Dometic still uses the "Turbo" name, and when we replaced our VCs the new units were DTU16s. Yes quieter, yes composite drain pan, yes more forceful air handler, etc.

"Quieter" has different components, though. Compressor noise went down. (That's without the optional noise shield, too.) Subjectively, not quantified; I didn't check dBs. Air noise at highest fan speeds went up a bit... I think because the newer units can push more air faster.

We found useful to cool the boat down at high fan speeds, then reduce fan speeds to settings 1 or 2... at which point the boat stayed comfortable and "wind" noise was negligible, almost not noticeable. Fan speeds are programmable, and I messed with the defaults a bit, too... to increase the difference between fan speed 1 and fan speed 6.

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Old 07-05-2020, 04:02 PM   #14
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I have the 12k unit and quite pleased. If you are in front of it- like line of site to the return air- you can hear it. Surprisingly if on top of it (it is under my v berth) it’s pretty quiet. I do not have the cover, but the place where it is installed is lined with soundproofing. It replaced the previous MarineAire unit which was marginally noisier.

I’m pleased.
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Old 07-06-2020, 09:54 AM   #15
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Self contained A/C unite have 3 main noise sources. The compressor, the fan, and velocity noise.

Scott C did an excellent job describing isolation of the unit and insulation and "tightening up" the cabinetry the unit lives in. Structure borne noise is typically dominant in self contained units, and proper isolation very important. Rather than grommets which provide some isolation, a real equipment isolator will provide better performance. Because these A/C units are typically held in place with clips that hold down the drip pan, installing the unit on a plate of aluminum or similar and extending 2 sides beyond the pan allows space for using isolators. Doing this also allows you to find the center of gravity of the unit and place the isolators where they will be equally loaded.

Something Gmarr mentioned deserves elaboration. Many A/C units are mounted right up against the return air grille. Proximity of the unit to the grill will directly effect how much mechanical air borne noise is transmitted. In a settee (or anywhere, under a berth, in a closet) if you can push the unit back a few feet from the return grille and create a baffle that will torture the noise path without choking the airflow it will significantly reduce mechanical noise coming through the grille. Apply anything soft to the side of the baffle facing the A/C unit, torture and absorb.

Last thing is velocity noise usually at the cold air outlets. If this is a problem (whistling) adding additional outlets will reduce velocity without reducing airflow, it will just slow the air down.

$0.02
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