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Discussion Starter · #1 ·
A couple of days ago I had 2 AC companies at my house to give me an offer on new AC split unit.
I decided to go with 3T 16 seer Rheem - this is good for the house, but I need advice on installation of inside unit. I have blower on top and coils on bottom and it all sits on wooden box - old system. It is in a closet in family room. It is loud and annoying when watching TV. The box has 18x18 air intake where I have air filter.
Now, 1 guy recommended removing everything and installing everything new on new metal stand with drip pan. This way there will be no 18x18 air intake restrictions, which is supposed to restricting current AC. Good.
But, the 2nd guy said that putting all on metal stand with drip pan will make everything louder since the current box also dampens the noise. He said that restriction that is from 18x18 air intake is much smaller than the increased noise that I will get from putting all on new metal stand.

I don't know what to do. I want quieter system but also efficient.

Any advice how to decide?

Thank you!

John D.
 

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layman (at least when it comes to sizing grills is concerned) speaking here, but wouldn't it make more sense to install a bigger intake or second intake?

18x18 sounds a bit small - will reduce the noise.

it will always be noisy with not much of a return duct.
 

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Can they put a larger intake?

Not sure what the air handler opening size is on the unit but my furnace that can do 3 tons uses a 16x25 intake. That is 400 sq inches and your 18x18= 324 sq inches. As it gets smaller it gets louder. Not sure what the minimum size is for your unit. Should be in the install manual.

I doubt it has anything to do with the stand. Most people use metal and put some rubber foam tape or rubber under the unit where it attaches to the stand to absorb vibration.
 

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Discussion Starter · #4 ·
Maybe I can cut bigger hole, so maybe 20x20 would be 400 sq inches, or similar size because then I need a new grille and filter size (I cut to measure the air filter anyway).
There was no talk about rubber or anything that would absorb vibration, maybe that is something I would need to do on my own, I guess.
 

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I doubt it will be much quieter because it is near your living room. Usually they are in a attic or basement. Once you get them in a closet the sound literally travels thru the grill to the outside room. A larger return opening and putting it on rubber will help but the nature of the setup is always loud.

A larger grill will cause the fan to use less elec $$ which should benefit you and it is less prone to freezing up from poor airflow. Can also get get better performance and freon pressures and readings with better airflow. Now may be the time to make a larger hole and do it properly.
 

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A larger grill will cause the fan to use less elec $$ which should benefit you...
Haha only if the installer is smart enough check static pressure and cut the speed.

otherwise as i'm sure you do a psc motor driving centrifugal fan will draw more with the lower static - stay at the same speed. (and move more air, which could reduce total consumption but the blower will draw more)
 

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The placement will limit the sound attenuation possible. I recommend getting an ECM with that new indoor unit. While at full speed they won't be much quieter, their partial speed is significantly quieter. Especially when they turn on/off. In many locations, the additional cost of the motor is offset in the electrical savings.

As a DIY project after they are done, you can install extra sound insulation on the walls of the cabinet. A small sheet of the same insulation can help with the line of sight sound through the grill. (held between the unit and the grill several inches away from the grill) It won't be perfect, but the effect will be noticeable.

Cheers!
 

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Discussion Starter · #9 ·
@supers05: so you recommend to get rid of the current box, let them install new stand, right?
As for ECM (I assume you mean 'variable speed' fan and not East Coast Mechanical as most Google hits suggest :)), I was told by the same sales guy that insists on keeping the box, that these are good for efficiency but he said that when the fan is starting and stopping the sound it makes seems like a plane is taking of and landing... and quieter the rest of the running, does this make sense?
 

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They slowly ramp up.

Very very quiet motors, the only noise is air noise. Variable speed/ecm can actually make a system more noisy with undersized ducts - as they ramp up to get proper airflow. Regular motors simply don't move enough air.
 

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ECM = electronically commutated motor and is a DC motor.

They are heavier built and have ball bearings vs sleeve bearings of standard PSC permanent split capacitor motors.

They ramp up in speed like a escalator at a store when you walk up to them or a walking escalator at a airport. When they start they rock back and forth a few times and kinda groan/chug as the motor sets itself up. But when running they are smoother and can be quieter as the tech can fine tune the speed of them to suit the ductwork and get better control of the freon pressures and air temp.

The nature of closet units is the sound travels thru the grill no matter what you do. I see them in mobile homes and slab homes where I am. I would get the hole made to 20x20 so you can use a standard filter from HDepot and get a metal stand and have them put it on rubber strips. Buy some 1" wide rubber and give it to them. They can also use some of the black pipe insulation from the freon lines.

Nobody can see your ductwork from here to know if it is badly undersized but I rarely have problems with them and undersized ducts as they have a wide range of speed. And yeah you will hear all kinds of horror stories on the net about worst case scenarios but those are rare.
 

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If i was doing the install, it would be a metal box with 1" insulation inside. The rubber would help too. We don't use wood for this application because of building codes, so I can't say how it performs.

Cheers!
 

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You can put elec furnaces but not gas straight on wood. Gas you need a combustible base adaptor or we just use sheet metal where I am.

I would not want wood if water leaked out of the coil as it could rot over time.
 

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The metal stand/return air box can have sound attenuation insulation put in it to minimize noise. For 3 tons, your return filter grille should be no less then 20x24.
 

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Discussion Starter · #15 ·
Yes, just checked and I can cut max 20x20 grille, maybe 21x21 if I improvise to hold it in place, which is not enough for 3T - should be at least 600 sq inches or no les than 20x24...
So, I guess it needs to be removed and put on stand with free flow. I'm just worried even if I ask the technicians/sales guys to put 'sound attenuation insulation', they would probably not do it or not do it right. I trust the sales guys would do it, but they don't do the installation - so, sales guys can say yes will do it, and then it won't be done or done poorly.
I assume once all new equipment is set, I can't really do anything on my own, right?
 

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The equipment is usually ordered via the salesman's notes. The installer just slams it in. The base would be ordered with the insulation already in it.

You could do a few things after they install it. In fact, while not exactly DIY friendly, the whole thing has been done on here before. However, most installers that i know, do a decent job. They'll be done quick, and it usually looks good after.

Pictures and will from you are the only things needed for us to help you after the install.

Cheers!
 
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