Posted: 5/30/2012 8:02:26 PM EDT
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I have had a new 3.5 ton Trane system installed to replace an old 3 ton Trane. The air handler is positive flow. As such, the fan motor sits on the bottom near the return while the old unit's fan motor was on top of the handler. It is not a variable speed fan. The noise level inside the house is so much louder with the new air handler....
Can anything be done? |
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As stated, get some duct liner, and cover the surfaces in the return air with it. If sheetmetal, you use spray on adhesive, and maybe some screws with washers. If it is a return air box of lumber, then some simplex type nails will work; nails with a large washer on the head. (They are for nailing down roofing felt.
You need the mat of material. Don't try hard foams of any kind, they don't absorb sound well. Now, onto this motor....... I am telling you, I think this motor is a 3 speed unit. FAU motors usually run high speed for fan/AC, and low speed for heat. The motor will have some inputs on it, or several wires leading from it to a contact/ junction panel. Try to read the schematic if possible; it should show the fan (Green lead from T-stat) hit its; relay and then to the motor. Look at that wire. Should be high speed. Now, follow the heat lead (White from T-stat) It should hit a different wire than the fan switch. (Do not undo the T-stat; the control panel will be color coded for the T-stat inputs. Work from there. I am willing to bet the motor has 4 leads coming from it; red, black, yellow/blue, and white. If the motor has only 2 wires, white and black..... you are correct, and it is a single speed unit. You can PM me if you would like a little help to walk thru this if you are game to investigate it further. As to the liner, there are 2 that would do the trick: Eggcrate sound dampening. No 'R' value, not itchy, easy to work with. Might not accept all adhesives, so your results may vary. Other option is duct liner roll. Like a black mat on the outside face, with 1" of fiberglass woven mesh on the back. Best found at a sheetmetal or HVAC shop. Itchy, has R value, does a good job and lasts. Hope this gets you pointed where you want to go. Good Luck, Paul. |
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Thanks for the input, guys.
My AH sits on top of a box in the garage. The intake grill is in my living room area. Originally, the box was not lined... studs and the back of the sheet rock was it. When the new unit was installed this intake area was covered with duct board. I asked for, and got the duct board liner installed so that the fiber part was placed against the studs.... the foil side of the duct board is inside the box instead of the fiber side - which is opposite of the usual. Is that contributing to the noise level? Also, although the intake itself is the same size as the previous intake, the size of the box was reduced when the installer lined it with duct board (more than just the width of the board... the size of the box was reduced). Let me know if this sounds like it will make a difference. I am going to call my installer about the fan speed. They just installed it (two weeks ago) and I am sure they will want to try and make me happy. |
| Look at the fan speed as mentioned above. On your AHU look at the circuit board, in one corner there will be a spot marked "fan connections", ther will be a red, blue and black wire at a minimum. Some Tranes come with a five speed motor. The schematic will list color/speed wires. Your new 3-1/2 ton AHU probably has a larger drive (more tonnage). Lower the fan speed by one speed. The installer should have made sure that you have enough duct work for the 1/2 ton increase. If not this will lead to increased sound level also. As a matter of fact, check duct sizing first. Your house is probably sized under or right at max static pressure to begin with. Most installers won't use the larger duct as it costs more. |
| The OP stated that the fan is on the bottom of the unit. With that sitting on you cold air return plenum(box), the fans right there. You will never get it to quiet up to the levels you want. Should of replaced with the same style of unit is the old one. Sure switching the fan speed around will help a little bit, but it won't give you what you are looking for. |
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Quoted: The OP stated that the fan is on the bottom of the unit. With that sitting on you cold air return plenum(box), the fans right there. You will never get it to quiet up to the levels you want. Should of replaced with the same style of unit is the old one. Sure switching the fan speed around will help a little bit, but it won't give you what you are looking for. Also a good point. Didn't catch that. |
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Quoted:
Thanks for the input, guys. My AH sits on top of a box in the garage. The intake grill is in my living room area. Originally, the box was not lined... studs and the back of the sheet rock was it. When the new unit was installed this intake area was covered with duct board. I asked for, and got the duct board liner installed so that the fiber part was placed against the studs.... the foil side of the duct board is inside the box instead of the fiber side - which is opposite of the usual. Is that contributing to the noise level? Also, although the intake itself is the same size as the previous intake, the size of the box was reduced when the installer lined it with duct board (more than just the width of the board... the size of the box was reduced). Let me know if this sounds like it will make a difference. I am going to call my installer about the fan speed. They just installed it (two weeks ago) and I am sure they will want to try and make me happy. Okay- WRONG LINER. Yes, it is making an echo chamber out of the motor. Swap that, it WILL help a bit. Second, you could add a second intake on an adjoining interior wall. Another option is to make the return air register opening bigger in the house if at all possible. Usually, the easiest solution. You don't need to cut studs, just remove drywall off them (Say you were going from a 24x14 opening, and you could fit a 30x14 opening. No major surgery necessary. The studs won't cause any grief. You may need to notch the studs inward 1/2" to fit a bar type register.) Also, if you do not have a bar type return register, get one. It will allow much more airflow than a stamped register. More flow means less squeeze on the air, increases volume and reduces velocity, and reduces noise. You are making progress, keep at it!! 
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To provide an update ....
Installer came by.... He showed us how to adjust the fan speed. It is a three speed unit, and was set in the middle. Putting it on low speed made little difference. We discussed adding another return to reduce air flow/noise. To simulate that, installer opened up the front of the air handler which was about the size of the existing return... so air was pulled from the actual return, and the front of the air handler so the air flow though the return was effectively halved. Noise level was not reduced enough. He is going to bring some duct board, and line the plenum with fiber side on the inside to see if the fiber side will absorb some sound. I doubt it will make a noticeable difference. Napahunter, I think you are right. They sold me on this unit because it was insulated polymer instead of sheet metal..... they also told me that the positive system was good as well (pushing the air through the coils instead of pulling it through - doesn't suck in air from the garage though leaks, instead the leaks are pushed out into the garage).... The noise level doesn't bother me too much, but my wife can't stand it. I have to admit that it is noticeably louder. By a significant margin. Just don't know what to do at this point..... |