New A/C system sounds like space ship landing

[mtrot]

Just had installed a complete Lennox system with variable speed furnace(SL280V). The furnace is indeed much quieter than the dinosaur it replaced, but it seems that when it is running on the slow heat speed, there is a constant whine or "singing" sound from the motor. It seems to run most all the time, and when it does shut off, it sounds like a space ship engine winding down. This can be heard through the register in the master bedroom and I find it aggravating me when trying to sleep. When the motor is spinning down, I can also feel the frequency of the whine in the walls near the unit.

The old furnace had a kind of spongy board underneath it, but my installers said they don't usually use such a board. I am thinking I need some type of vibration absorbent material that the unit can rest on. Any thoughts?

[tinknocker service tech]

sounds like harmonic noise from a return grille caused by higher air flo
spread the fins on the grille so as to change the angle they are on and may help

could also be a bearing in the motor that wasnt oiled at the factory and the motor needs replacing

call your installer back and have it looked at
tell him all your concerns about the unit and see what he comes up with

[mtrot]

sounds like harmonic noise from a return grille caused by higher air flo
spread the fins on the grille so as to change the angle they are on and may help

could also be a bearing in the motor that wasnt oiled at the factory and the motor needs replacing

call your installer back and have it looked at
tell him all your concerns about the unit and see what he comes up with

Thanks, yes two different techs from the installer have come by and listened to the furnace fan. They say that is how the new fan motors operate. The whine is definitely coming from the fan motor.

[mtrot]

I do understand where tinknocker is coming from.

Mind if I ask some other questions? Is the harmonic noise coming from a supply or return (sorry, if my next question is simplistic, but sometimes one has to ask: does the air blow out or is it pulled in?) Is your ductwork all metal? Is the unit sitting on a wooden floor?

I noticed you said it is vibrating the walls near the unit although you have harmonics at one area only. It is hard to diagnose without seeing, and sometimes, it is the design of the original system (sorry, all components do need to work well together and that includes original ductwork, registers and grilles) that creates that very annoying "pitch." And of course, I have other questions, but this should help get the conversation going in the right direction for everyone.

Thanks, the whine is coming from the fan motor, but I can hear it through the register in the master bedroom. The furnace/coil unit is sitting on a wood base in a closet in the middle of the house. What I'd like to do is isolate the furnace from the wood base it sits on, as well as from the nearby walls.

[mtrot]

The real easy answer would to ask them to install iso pads, and they should not have objection to this.

Is this over a crawlspace or basement?

Keeping mum on other questions for now, sorry. But not seeing it in person, I know these are very quiet units.

Pics of the install:

http://inlinethumb08.webshots.com/17671/2054906870041505722S600x600Q85.jpg (http://home-and-garden.webshots.com/photo/2054906870041505722AdzNGQ)

http://inlinethumb02.webshots.com/49793/2480676140041505722S600x600Q85.jpg (http://home-and-garden.webshots.com/photo/2480676140041505722AKrEbV)

As they say, a picture is worth a thousand words. It sits on a wood shelf in this closet. And yes, Lennox claims it is the quietest operating furnace on the market. It is not the air induction noise that is the issue. It is that the motor has a constant high pitch whine when not on the fast speed. Unfortunately, it spends 90% of the time on the lower fan speed, at which the whine occurs.

What are these isolator pads you mentioned? Wouldn't they need to be such that they supported the entire perimeter of the base, so that no closet air could enter the furnace? As you can see, the filter base sits directly on a plywood board. Thanks again.

[thermojohn]

The noise you mentioned is coming out of the supply grille in the master BR? How close is it in relation to the furnace closet. Looks like you have plenty of filtered return opening for 5 tons, so I don't think it is return velocity noise. You have second'ed that.

The whine you hear is the motor. I have a variable speed (ECM) motor in an A/H next to my office. It is also two speed, and when it is in low speed, it also has a whine. It's caused by the 'cogging' of a permanent magnet motor and is in its nature.

You might be able to 'tune' the harmonic you are experiencing out by making a slight adjustment in speed to the motor. Call your installing company, and see if they could make a small adjustment in speed to the motor. There is a small window to work with as it is also important that the motor is @ the right RPM as correct airflow is important for your system's efficiency and performance. But a small % either side of your harmonic just might remedy the situation.:.02:

[hearthman]

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[precision hvac]

I see several things wrong w/ install but it has nothing to do with the noise you hear.
On the install- the gas line where it passes through platform must be sealed. Base of filter box must be sealed to platform. Furnace must be sealed to filter box or EZ base.
I don't see a trap on that condensate drain from coil.

On the noise- may be a bad motor. Did you have ducts replaced?

[thermojohn]

I don't see a trap on that condensate drain from coil.

The drain typically runs in a chase under the slab, then exits above grade creating the required trap. Typical install.

[SBKold]

Remove filter in base of unit and see if it goes away.

[mtrot]

The noise you mentioned is coming out of the supply grille in the master BR? How close is it in relation to the furnace closet. Looks like you have plenty of filtered return opening for 5 tons, so I don't think it is return velocity noise. You have second'ed that.

The whine you hear is the motor. I have a variable speed (ECM) motor in an A/H next to my office. It is also two speed, and when it is in low speed, it also has a whine. It's caused by the 'cogging' of a permanent magnet motor and is in its nature.

You might be able to 'tune' the harmonic you are experiencing out by making a slight adjustment in speed to the motor. Call your installing company, and see if they could make a small adjustment in speed to the motor. There is a small window to work with as it is also important that the motor is @ the right RPM as correct airflow is important for your system's efficiency and performance. But a small % either side of your harmonic just might remedy the situation.:.02:

Thanks so much. That is very helpful info. I will get them to vary the speed a bit and try to mitigate the whine.

Yes, I can hear the motor whine through the register in the master bedroom. Sounds just like it does elsewhere in the house.

[mtrot]

Remove filter in base of unit and see if it goes away.

Thanks, I already played around a bit with the filter. What happens is that if I pull the filter out about 5 or 6 inches, the fan will speed up dramatically. If I remove the filter completely the fan will speed up for a while, and then it slows down significantly. I am assuming it has some kind of air flow sensor that realizes that without the filter it can achieve the same air flow with less fan power.

I also replaced the pleated filter with a standard fiberglass type filter, which seemed to reduce the motor whine a bit, presumably again due to freer air flow.

[SBKold]

I mentioned the filter because it should be a significant restriction causing your unit to struggle to move the proper amount of air.

Increasing or decreasing fan speed away from what it is optimal to run is not helping the system be as efficient as its SEER, AFUE, ratings.

You may have better, quieter results by redesigning that part of it.

[precision hvac]

3M Filtrete in it before?
Sounds like filter was very restrictive before.

[mtrot]

3M Filtrete in it before?
Sounds like filter was very restrictive before.

It was not the brand 3M Filtrete, but basically the same thing. Yes, the fiberglass one is less restrictive, but still have the motor whine.

[mtrot]

Well, it looks like I am just out of luck with trying to get rid of this motor whine. I tried a plain fiberglass filter, and it may reduce the whine slightly, but it is still quite apparent throughout the house.

My installing dealer has gone to heroic efforts to mitigate the whine, but with no success. They have sent several different techs on several different occasions to try to deal with this issue. They did try adjusting the motor rpms, but the motor whines at any rpm. It whines the least at full rpms, but the problem is that these variable speed systems are designed to avoid full fan speeds.

Then, they installed insulation panels on the interior walls of the closet in which the furnace sits. They also installed some insulation on the concrete flooring of the closet, directly under the furnace. The problem is that the motor whine just comes right out through the return air intake vents at the bottom of the closet walls.

Then, the top tech called one day and said he had the Lennox area rep with him, and wanted to come over with the rep and check out the problem. They came by and listened to the whine for a while, and then the rep said he wanted to warranty the motor and install a new one. They did come the next week and install a new motor. However, the new motor has exactly the same whine as the original one.

Now, the installing dealer and the Lennox rep both say that all these DC variable speed motors have this motor whine. My old unit which was replaced had no whine at all.

So, it appears I am stuck with this motor whine, as I am told and have read that all brands, including Trane or Carrier, have this motor whine. I would say that these new blowers are fine if they can be installed in the attic or perhaps in a closet that is located just outside the living areas of the house, perhaps the garage area. All I can say is, having to put up with this constant whine better result in some noticeably lower energy bills.

[thermojohn]

Well that is a bummer. Sounds like they tried all they could do. Those motors do have a whine due to the 'cogging' effect inherent with ECM motors. The configuration you have (including your unit's location, and all other factors) may create a sound box similar to an acoustic guitar that amplifies the sound, and carries it through your home. Or you are very in tune with that harmonic. Is this a 2 speed system? Sorry if you have posted it earlier, and I missed it.

[mtrot]

It is a variable speed furnace, with two stage burners, if I am not mistaken. Lennox SL 280V.

No, it is not a "sound box" situation. Because I had that concern, they insulated the inside of the closet. The motor whine simply travels out through the return air intake vents, of which there are three. I would like to explore some ways to isolate the motor housing from the furnace where it attaches.

[Mr Bill]

If the noise is coming from the motor, there is not a lot your going to be able to do with that application. If you can, you might take some duct board, and insulate the inside return walls were you can, and maybe even lay a piece of the duct board down on the floor of the return area also. This "might" help adsorb some of the noise, and if it don't help it sure won't hurt anything.

[energy_rater_La]

I agree that the ductboard may help to insulate the sound.
I'd do the full return walls and floor.
if that doesn't help then the walls and door (which should have
been done anyway) of the upper part of the closet where
unit is located.

best of luck.

[Mr Bill]

Short of a miracle, the only solution I see you have is, to build a chase box into the attic on the side of the furnace closet, and run a duct off it to a return in the ceiling. I know hindsight is always 20/20, if the contractors that are selling these, and if the motor noise is common, and also common with other mfg. they should make the customer aware of this, especially in a closet application.

[Firebird A/C]

mtrot: Looks like you may be short on return air to the furnace, or the stamped face return air grilles you have are to restrictive. To get more air going through the existing return grilles you have, take your needle nose pliers and bend open every louver on each return grille. Or better yet pull off return grilles. Run furnace and see if noise is better or same.
Why home builders sit a gas furnace in the hallway next to bedrooms is crazy. It is just noisy to sit in the middle of the house. Furnace should be in garage.

[Mr Bill]

mtrot: Looks like you may be short on return air to the furnace, or the stamped face return air grilles you have are to restrictive. To get more air going through the existing return grilles you have, take your needle nose pliers and bend open every louver on each return grille. Or better yet pull off return grilles. Run furnace and see if noise is better or same.


Read previous posts, he has already tried all that and determined the noise is from the motor.

[beenthere]

Post pics of the furnace and the return grilles.

[mtrot]

Thanks for the replies! Yes, as you can see from these pics, the installers, on one of their return trips, installed sound deadening panels on the interior walls of the closet, as well as the closet door. Also, at the time of the original installation, they installed sound absorbent material to the concrete flooring of the closet where the air comes in.

http://inlinethumb38.webshots.com/46693/2721036830041505722S600x600Q85.jpg (http://home-and-garden.webshots.com/photo/2721036830041505722IwzBLA)

http://inlinethumb23.webshots.com/47382/2986347760041505722S600x600Q85.jpg (http://home-and-garden.webshots.com/photo/2986347760041505722kICbjW)

http://inlinethumb62.webshots.com/50173/2158213170041505722S600x600Q85.jpg (http://home-and-garden.webshots.com/photo/2158213170041505722EMQjKM)

http://inlinethumb12.webshots.com/49675/2620677350041505722S600x600Q85.jpg (http://home-and-garden.webshots.com/photo/2620677350041505722rxpBxB)

http://inlinethumb51.webshots.com/46898/2757042800041505722S600x600Q85.jpg (http://home-and-garden.webshots.com/photo/2757042800041505722SPJjOT)

I think the idea of building some type of chase to move the air induction area farther away from the motor is a great idea, but considering there are hallways on all three sides of this closet, I'm not sure how that would be possible.

[mtrot]

mtrot: Looks like you may be short on return air to the furnace, or the stamped face return air grilles you have are to restrictive. To get more air going through the existing return grilles you have, take your needle nose pliers and bend open every louver on each return grille. Or better yet pull off return grilles. Run furnace and see if noise is better or same.
Why home builders sit a gas furnace in the hallway next to bedrooms is crazy. It is just noisy to sit in the middle of the house. Furnace should be in garage.

Thanks. Well, that issue came up in the installation, and because of the possibility that there was insufficient return capacity, calculations were made, and they added the grill on the left wall side of the closet(there were previously only two intake grills), resulting in three intakes now. With the three, I am told there is ample intake capacity for this 5 ton system. Plus, after they added the third intake, there was no difference in the whine. Also, we have run it briefly with no filter in place, and it still whines, just a bit less pronounced. But you have to have some kind of filter in place.

[thermojohn]

One detail I see... If I am trying to attenuate blower or furnace noise with duct board, I always put the fiberglass side facing the source of noise, so that it will be absorbed. The foil side only causes the sound to bounce around until it finds a way to escape. The return floor has the fiberglass side or foil side visible?

Picture please. :grin2:

[Mr Bill]

I was talking about duct board in the return area below the unit, not in the closet area.

[Mr Bill]

One detail I see... If I am trying to attenuate blower or furnace noise with duct board, I always put the fiberglass side facing the source of noise, so that it will be absorbed.
Picture please. :grin2:

Correct! but they should have placed it in the return area itself, in the way you described.

[mtrot]

One detail I see... If I am trying to attenuate blower or furnace noise with duct board, I always put the fiberglass side facing the source of noise, so that it will be absorbed. The foil side only causes the sound to bounce around until it finds a way to escape. The return floor has the fiberglass side or foil side visible?

Picture please. :grin2:

I was wondering about that, but I went with the way they wanted to do it. Actually, the pieces on the left and right sides of the furnace were simply slid into place, so I will try to remove them and insert them with the fiberglass side facing in towards the furnace. May be a problem on that right side because of the gas line and drain pipe in the way.

The insulation on the slab underneath is not the same type as what is in the upper part around the furnace. It is about 1 inch thick, black, and has R-40 printed on it.