AS air handler noise problem potentially fixed--pics of my solution inside. Thoughts?

[Lugh]

Hi all,

I think I've found the solution to my noise problem with an open return 4-ton AS GAM5 air handler. As many of you may recall, I've been tossing around the idea of replacing a louvered bi-fold door with a solid slab door with a 24x24 filtered return in it.

Not wanting to spend a few hundred bucks on a door, I went to Home Depot and bought myself some 3/4" rigid insulation, a 1/2" piece of soundboard, and the return. I then cut the insulation and the soundboard to fit my air handler closet and installed the return in the insulation.

Here are the sound meter readings:

1) Louvered bi-fold door: 62 dB
2) Insulation/soundboard, return on bottom: 56 dB
3) Insulation/soundboard, return on top: 52 dB

As you can see, I am able to reduce the sound by about 10 dB if I were to put a slab door with some soundboard on the back in place of the louvered door. Since the blower is on the bottom and is the cause of most of the noise, I was wondering if putting the return on top might further muffle the noise from 56 to 52 dB or if that would starve my system for air. I have noticed no whistling or other signs of air starving. Pics below.

So what do you all think? Would it be a bad idea to install a door w/ a return on the top for maximum sound deadening?

[skippedover]

From the look of things, the filter grill appears to be the same size as the blower inlet. Not knowing the size of the equipment I cannot make an accurate determination as to the appropriateness of that opening. What I can say is that the grill you've installed is about 25% less open area than the opening into the air handler. In that regard, you should ideally increase the size of the grill by a minimum of 25%.

[Lugh]

It's a 4-ton American Standard GAM5 air handler and the size of the return under the unit is 22"x20". In addition to the 24x24 filtered return you see pictured, I also have a 12x12 filtered return in a room that shares a wall with the AC closet, so I think I've got enough surface area. With that said, does it make a difference in terms of airflow whether I have the return on the top or the bottom of the door? The top is a good deal quieter.

[Shophound]

At the top, air will need to squeeze between the door and the air handler. At the bottom, straight shot.

Deaden the sound at its souce. Take some soundboard and line the chamber below the blower intake with it. Fasten it down well so the blower cannot pull it up. Next, do your door idea with the filtered return at the bottom. Remeasure your db level and see if that gets you closer to the lowest number you measured above.

[Lugh]

At the top, air will need to squeeze between the door and the air handler. At the bottom, straight shot.

Deaden the sound at its souce. Take some soundboard and line the chamber below the blower intake with it. Fasten it down well so the blower cannot pull it up. Next, do your door idea with the filtered return at the bottom. Remeasure your db level and see if that gets you closer to the lowest number you measured above.

And squeezing the air is a bad thing? With the soundboard box, would I just leave the front open and have panels on the other sides?

[George2]

First, you should add a filter grille to the other wall (in the office?). Not enough open area now.

I disagree will #4, keep the grilles high. I think that will be more quiet. But test it to make sure.

[Lugh]

First, you should add a filter grille to the other wall (in the office?). Not enough open area now.

I disagree will #4, keep the grilles high. I think that will be more quiet. But test it to make sure.

I've got a 12x12 in the office, so in total I've got a 24x24 and a 12x12.

[George2]

I've got a 12x12 in the office, so in total I've got a 24x24 and a 12x12.

That's good for 1,440 cfm. You need at least 1,600 for a 4 ton drive. More area will decrease the noise.

I would recommend filter grilles (for each grille). That will add addition bufferting.

[vstech]

also, blower noise is due to sound wave reflective surfaces in line with the openings.

if you install rough surface insulation in the blower compartment/plenum area and perhaps build air baffles that do not obstruct airflow, your noise will all but disappear!
how much room is there between the front of the air handler, and the doorjam?

[Lugh]

also, blower noise is due to sound wave reflective surfaces in line with the openings.

if you install rough surface insulation in the blower compartment/plenum area and perhaps build air baffles that do not obstruct airflow, your noise will all but disappear!
how much room is there between the front of the air handler, and the doorjam?

About five inches of room between the air handler and the door jamb. What kind of rough surface insulation would you recommend?

[George2]

I double read your post and it is true......higher is quieter.

[Shophound]

How do you plan to permanently affix the insulation board, regardless of where you ultimately choose to put the filter grill? Right now, with it laid over the opening as you show in the photos, air is bypassing the filter and board near the baseboard, as best I can tell.

There may be more room between the board and the front of the air handler for air to pass than appears in the photo, but I would still estimate it is less than having the filter grill at the bottom. If you want to get geeky about this, get a manometer and a static pressure tip, and check static pressure with the various configurations. Any lower number over another will mean whatever configuration gave you that lower number is less restrictive than others. That may not coincide precisely with your sound reduction goals...that's why I suggested lining the bottom of the closet with sound board.

Whether this closet has a louvered door or you go with a solid piece with filter grill, either method puts the entire closet into a negative air pressure state compared to everything around it. If that closet is below an attic, and there are penetrations in the ceiling of the closet to the attic that are not tightly sealed, attic air will pull in every time the unit runs, adding heat and dust to your system. Something you may want to check out if you haven't done so already.

[Lugh]

The insulation board is going to be tossed in the trash. Right now I'm just using it to mimic a door without having to actually buy and hang one. The sound board will be attached to the back of the door using spray adhesive.

Attic and dead space between floors are well-sealed, but I intend to line the bottom of the closet as you suggested anyhow. I think I might try your manometer suggestion, provided I can get my hands on one that I can then return to home depot afterwards

And just to be clear: even with the current louvered door, the closet is in a negative air pressure state?

How do you plan to permanently affix the insulation board, regardless of where you ultimately choose to put the filter grill? Right now, with it laid over the opening as you show in the photos, air is bypassing the filter and board near the baseboard, as best I can tell.

There may be more room between the board and the front of the air handler for air to pass than appears in the photo, but I would still estimate it is less than having the filter grill at the bottom. If you want to get geeky about this, get a manometer and a static pressure tip, and check static pressure with the various configurations. Any lower number over another will mean whatever configuration gave you that lower number is less restrictive than others. That may not coincide precisely with your sound reduction goals...that's why I suggested lining the bottom of the closet with sound board.

Whether this closet has a louvered door or you go with a solid piece with filter grill, either method puts the entire closet into a negative air pressure state compared to everything around it. If that closet is below an attic, and there are penetrations in the ceiling of the closet to the attic that are not tightly sealed, attic air will pull in every time the unit runs, adding heat and dust to your system. Something you may want to check out if you haven't done so already.