Forced Air Furnace Noise

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  #1  
Old 11-19-02, 08:33 AM
Heiko
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Question Forced Air Furnace/AC too noisy

I have a forced air furnace in the basement. There is on larger register for air intake on every floor of the house. The problems is that these registers make a lot of noise whenever the heating/AC comes on. Is there any way I can dampen this noise with a filter or something else?
Any help would be really appreciated.

Thank you.
Heiko
 
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  #2  
Old 11-19-02, 11:22 AM
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NOISE

If the duct are big enought you could line the inside with whats called ductliner. IT will help ED
 
  #3  
Old 11-19-02, 11:32 AM
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Heiko:
You should be able to do some detective work to determine if the noise from the fan is being carried through from the furnace or the noise is from too much air velocity. Too much velocity makes a wooshing or whistling sound.
 
  #4  
Old 11-19-02, 11:44 AM
Heiko
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From what I can tell it is not the fan.
It is really airflow that is generating the noise.

What is ductliner? Just some kind of dampening
material that goes into the pipes or the register?

Thanks for the help so far.
 
  #5  
Old 11-19-02, 11:56 AM
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Heiko:
Yes ductliner as Ed suggested is pressed fibreglass. It is sold in sheets or rolls in various sizes and is held to the inside of the duct by either adhesive or clips.
The down side is that it tends to collect dust and is difficult to install on an existing system.
You might try removing all the grills to see if that changes anything. See what that does and maybe after that there are a few tricks you can try.
 
  #6  
Old 11-19-02, 11:59 AM
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blower

There ya go thats it . Or there is whats called duct board its made out of insulation and has a cover on it. you can get some of this and put it in the duct. Also would there be a way that you could cut them out and put in a bigger cold air registers? ED
 
  #7  
Old 11-20-02, 06:03 AM
Heiko
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Thanks for the input so far.
Let me sum it up. I think putting in a larger
register is not an option.
I can either install duct liners. How deep into
the pipe does that have to go to make a difference? Does anybody have a ballpark on that.
I mean for sure there is only so far I can reach into the pipe. One more thing about since that is
decreasing the diameter of the pipe would that have a perfromance impact?
Or the other option is installing duct board and
that goes directly into the cutout for the register. Is that correct?

Thanks so much, guys.
 
  #8  
Old 11-20-02, 08:46 AM
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Heiko:
Have you removed all the grills from the return air registers to see what effect that has?
 
  #9  
Old 11-20-02, 09:14 AM
Heiko
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No I haven't tryed that but I would assume that some of the noise goes away.
 
  #10  
Old 11-20-02, 09:33 AM
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noise

Why cant you put in bigger cold air grills? Are you short on the return. could another one be put in ???? ED
 
  #11  
Old 11-20-02, 10:12 AM
Heiko
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Sorry Ed, I think I misunderstood.
Do you mean a bigger grill or bigger
pipes (larger diameter)?
If you mean the grills, I didn't even know
you can get different sizes.
 
  #12  
Old 11-20-02, 11:00 AM
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blower

Cold air grills go big big big as you need.As I dont know how your cold air pipe or duct is set to the wall or what ,its hard to just say.
Can you say how many tons the AC is and how big is the furnace.
Ok now just how big or how many cold air pipes or duct go back to the furnace. Like what is the tot. squar" return that the furnace
gets ? ED
 
  #13  
Old 11-21-02, 06:06 AM
Heiko
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Ed, I have three register (one per floor).
The pipe diameter is about 10". What I don't understand is why do you think that putting a larger register would make a difference? In order to reduce the speed of the airflow I would have to put larger pipes and that would be an undertaking next to impossible. Or am I missing something?

Thanks for sticking with me on this one.
Heiko
 
  #14  
Old 11-21-02, 10:12 AM
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blower

Now ??? How many ton is the ac? Is that just one 10" pipe?OR do you have 3--- 10"pipes that go all the way back to the furnace. Like GregH said what is it like when you take all the cold air grills off ED
 
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Old 11-21-02, 10:57 AM
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Heiko:

Moderator note:

Heiko wrote:
"No I haven't tryed that but I would assume that some of the noise goes away."

We can't help you if you don't help yourself!
 
  #16  
Old 11-21-02, 11:52 AM
Heiko
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I mean even if some of the noise goes away by taking the grills off, what is the benefit of doing that? I can not just leave those big holes
in the wall uncovered.
 
  #17  
Old 11-21-02, 11:54 AM
Heiko
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Ed,
I have get back to you tommorrow on your question.
I would assume these are different pipes coming from each floor, but I have to double check that.

-Heiko
 
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Old 11-21-02, 01:18 PM
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return air noise

First lets see if the noise goes away by removing the side panel where the air filter is. I'm sure it does. The noise is from the undersized return air duct. I'll bet the supply duct is larger than 10" . A 10" duct is for a max of 1 ton (or 12,000 BTU/hr). It sounds like you have at least a 2 ton unit and possibly 3 ton unit to do three floors. To determine the tonage look at the model number on the condensing unit and MOST manufacturers will have numbers like 012 for 1 ton in it or 018 for 18,000, 024 for 2 ton,030 for 2-1/2 ton, 036 for three ton ect.. What is the make of the unit?
The unit requires 400 CFM for each ton of AC. Keep in mind that as you increase the return air volume your AC output will increase as well and cool off the space faster, use less power ect...
A properly designed and sized system is at least half the cost, but you wont even hear the air, only the affects.
Duct liner is more like an impregnated horse hair blanket material. To secure it, you could use 3M spray adhesive available at Home Depot for about $7.00 a can. Don't run the unit for about 30 minutes when done. This stuff sets up extremely fast and works like contact cement. When it touches you can't shift it around. Dry fit it in place and fold it back, spray both surfaces, wait about 15-20 seconds and press in place, do half at a time. Now if the diameter was too small this will make it even smaller. I think you need to add on a return. Even if it's in the first floor space only thru the floor near a hallway.
A 10" round=about 408 CFM! We need to know the tonnage to start with.
 
  #19  
Old 11-22-02, 04:50 AM
Heiko
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Okay I try to give you guys all the information I was able to find last night.
The Furnace is named Silhouette,
model number: UGDJ-07EAUER
There was a sticker on it that says that the maximum input is 75,000 BtU/hr.
There are two pipes for the cold air return.
One is only about 30" inches long and about 9"
in diameter. The second one is a rectangular duct
12"x13" that goes from the basement all the way to the second floor. It leads to 2 registers, one on the first floor and one on the second floor.
I took the grills off and the noise stays the same if not even louder. It seems that the noise is really created by the air rushing through the pipes at high velocity.
Let me know if that information is sufficient.
I have the furnace installation instructions too.

Thank you.
-Heiko
 
  #20  
Old 11-22-02, 05:31 AM
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Heiko:
If you've removed the grills and the noise remains the same then you should remove the fan access door on the furnace as was suggested. This will reduce the airflow in the return ducts by creating another path for the air to return. If this makes a big difference in the noise level, it would indicate that your ducts are not large enough. Lining the ducts will have little effect as this will also decrease the inside diameter. Unfortunately I cannot see a fix other than to increase the duct size or add new ducts to reduce the air velocity to an acceptable level.
At first glance the return duct is about only half the size it should be.
 
  #21  
Old 11-22-02, 05:43 AM
Heiko
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Wow that is shocking. Lets say I am going to add
one/two more duct. Is there anything I have to be aware of? Is there something like a minimum length for a return pipe? If not I could just let them end right in the utility room where the furnace is. One more thing do I have to be careful not do overdo it? I mean is it possible to have too many (too large) return pipes?

I really appreciate your help.
-Heiko
 
  #22  
Old 11-22-02, 06:47 AM
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Heiko:
Return air pipes cannot really be too big, they just have to be balanced throught-out the house.
You should return a similar amount of air from each area of the house.
I'm sorry but I don't have my sizing charts handy and I'm packing up for a week-end in the big city.
Someone may come along with the return air size requirement for your furnace.
You likely could add a new return line to the main floor which is not really that big of a deal.
Where does the 9" round go?
 
  #23  
Old 11-22-02, 07:03 AM
Heiko
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Greg,

the 9" round one ends in the bedroom that is adjacant to the utility room (finished basement).
The easiest thing for me would be to run another pipe within the basement.
Getting up to the first floor is going to be much harder because of very limited accessibility.

Thank you Greg, you've been a big help.
Have fun in the big city.
-Heiko
 
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Old 11-22-02, 07:43 AM
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Heiko:
It is possible to increase the RA in the basement. What may happen though is that the supply air to the second floor could be reduced. To experiment you could open the door to the fan compartment slightly and tape it in this position.
See what happens.

I'm really going now!
 
  #25  
Old 11-23-02, 12:25 AM
lynn comstock
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Originally posted by GregH
Heiko:
It is possible to increase the RA in the basement. What may happen though is that the supply air to the second floor could be reduced. To experiment you could open the door to the fan compartment slightly and tape it in this position.
See what happens.

I'm really going now!
As a brief test to check the noise difference, this is OK. DON'T leave it that way. If the basement goes into a negative pressure (because of the open fan compartment door) the combustion gasses may not go out the flue properly. The fan may even pull in air down the flue pipe. This is called backdrafting and its a KILLER.
 
  #26  
Old 11-23-02, 10:29 AM
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Its tonnage

Its still not too clear of the tonnage of the unit. Silloutte is not a common Brand name we're farmiliar with. Try this look at the compressor and get the numbers from it. It will usually be either a Copeland or Techemseh compressor. I hope the condensing unit is not 7 ton as it MAY be by the Model number having the 7 in it. If so the return would be Grossly undersized.
Lets try this for starters, What dimensions of the plenum supply duct coming off the air handler? Is there a retun duct in each room?
Looking at the Return side, what is the dimension of the duct comming DIRECTLY off the plenum box of the air handler in fron of the air filter? For example if you come off with a 10" connection to the plenum and use a tee to a couple of 9's, it still only counts as a 10 " because it still has to draw the air thru the 10" diameter hole.
Secondly, I suspect this is a direct drive unit fan motor, and has a 3 speed option. These usually have taps you can move around. Try moving the high speed tap (Balck) to medium. Look at the installation instructions to see that. This is one way to help reduce the noise. You could also go throughout the house chocking down the supply outlets.
 
  #27  
Old 11-25-02, 05:53 AM
Heiko
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As you can probably tell by now I am really not an expert on Furnaces,but doesn't the 75,000 BtU/hr give you information about the tonnage?
Can you give me a hint where to find the compressor information?
No there is not a return duct in every room.
There is one register in the basement, that is the one connected to the 9" round pipe. Then there is one register on the main level and one register on the upper level. Both feed into the same duct which is the 12"x13" rectangular one.
Both of these duct are connected to the base of the furnace. I guess that is what you refer to as the "plenum box", because that is right before the air filter.
I have to double check the installation manual, but so far I did not stumble across any information about multiple speeds.

Just for my understanding. This house is a new construction and about 15 month old. The HVAC was installed by professionals. Could it really be possible that they hopelessly undersized the return air side??
 
  #28  
Old 11-25-02, 07:39 AM
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COLD AIR

There ya go "would they undersize the cold air" YES YES YES.They do it all the time. ON about 75% of jobs we go on it's that way. Sometimes the duct is ok but the hole for the air to get through is to small. Like had one cold air return duct 12x12 144" for 3 ton need 180" to 240" for it.Now the speed most of the time the blower is set on high for the A/C and slower for the heat. look on the blower door some times it will show you the speed lay out there ED
 
  #29  
Old 11-25-02, 09:05 AM
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Heiko,

I don't know what state you are from??

I've grew up here in Minnesota, and I never seen one return air for each floor.. I'd say that way undersized!! But then I've seen one big 20x20 return on each floor in Fla, when i was down there a few years ago..

Here we put returns in every room of the house.. Not in the bathroom and kichen.. (Order issues!) hehe

I almost have a feeling that your installer undersize the return, and your going to get a rush of air going into it, and that cause the noise...
 
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Old 11-25-02, 09:11 AM
Heiko
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Hi Jay,

I live in Virginia.
I agree with you. That is exactly the feeling I have. I just want to get some numbers down so I can try figuring out a solution. Now that the house is done I am afraid it is going to be almost impossible to get a return air pipe into every room.
 
  #31  
Old 11-25-02, 10:16 AM
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returns...

Returns aren't required in every room. Better installations do. Cheaper ones don't. Result; sometimes rooms don't cool off or heat enough, solution, keep the room door open or undercut the door about 3/4". Problem with this is that as the air passesd under the door it makes the rug an air filter sometimes, and you'll see dirt streaking under the door. Now you'll know why. the duct size you have is OK for a 2 ton or 24,000BTU unit. To see the tonnage tell us the model #of the condenser outside. Or the model number of the big black can in the outside unit, either a metal tag or a white one on the top of it. The motor speed is determined by the wires comming off the motor for the furnace, tell us the number and color of the wires coming out of the furnace motor.
 
  #32  
Old 11-25-02, 11:45 AM
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blower

If you want to check the rooms out for cold air. Open the door about 1" on the rooms. Then go turn the blower on if they go shut on you cut some more off the bottom of the door ED
 
  #33  
Old 11-26-02, 05:13 AM
Heiko
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Thanks for the advice, Ed.

Here are the numbers that I got from the unit.
The condenser pump has a sticker on top with this model number: KT-15X-1UL
On the side of the condenser I found this number:
RCBA-3765GG17 with the digits '65' beeing underlined.
Other than that there is a company logo RUUD on the unit.
Here is the motor wiring:
2 Brown wires going to a 7.5 MFD capacitor
1 white going to motherboard (labeled neutral)
1 red going to motherboard (labeled M1)
1 blue going to motherboard (labeled Heat)
1 black going to motherboard (labeled Cool)

I hope that is the information you guys are looking for.

Thanks
-Heiko
 
  #34  
Old 11-26-02, 05:05 PM
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motors...

you have a 3 speed PSC motor. All three speeds are hooked up (thats unusual)
Ill try find out tommorow what the tonnage is, I think Rudd has an OEM compressor, Ill get you a cross and let you know. In the mean time, have you tried to pull the panel cover off the blower to see if its still noisy? then place it 1/2 way on (the suction will hold it in place), is it noisy there? are all the return registaer fully open? Has it always been this noisy or is this something recent?
RSVP........
 
  #35  
Old 11-27-02, 04:23 AM
Heiko
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Yes, I took the panel off the blower compartment. I think it makes a subtle difference but not much.
Placing it 1/2" away is kind a tricky. I mean it is just a panel which you can take off or put on, nothing in between . Plus underneath there is a switch which prevents the furnace from running while the panel is off. I had to tape that down for the experiment.
All the return air registers are open.
Yes, it has been that noisy from day one.
 
  #36  
Old 11-27-02, 07:30 AM
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Noise???

If you removed the the panel door to the compartment that had the blower fan in it, and the noise was still there!!! Its not comming from the returns!
Try chocking down the supply regiters, the system may be too big or not enough drops...I don't understand why you didn't get the guy that put it in fix it? Are you really hearing loud noise? Have others said it was very loud or are you overly sensitive to this? Have you had warm air funraces before?
 
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Old 11-27-02, 09:21 AM
Heiko
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Isn't it possible that even opening the blower compartment did not supply enough airflow. I mean that is not a really big opening.

Why I didn't complain during the final inspection of the house about the noise? Believe me I ask myself that question a million times, but back then I thought this is normal.

What should I expect from choking down the returns?

> "Are you hearing a really loud noise?"
Let me explain it like this. In rooms where there is no return register it is very hard to tell whether the heating is running or not. You have to focus hard to hear some noise from the registers.
I like that part! In a room with a return air register like our living room you have to turn the TV a couple of notches louder when the heat comes on. I hate that!

It is possible that I am sensitive to this. My wife for example couldn't care less. But on the other hand if you hold your hand into the return air-duct you can feel a really strong and fast flow so that theory with the undersized duct really makes sense to me.

No I don't have much experience with forced air heatings. I am from Europe and that kind of heating is not used over there.
 
  #38  
Old 11-27-02, 11:31 AM
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I will try to summarize all this for you.

Heiko:

You may be suffering from information overload by now.

It is safe to say that the noise you are experiencing is coming from your furnace.
I can further say that it MAY be coming from the return air grills.
You say that you removed the door from the blower compartment and it didn't make much difference.
As long as all the doors were open to the basement when you removed the blower door, the air velocity in the return air should have dropped considerably.
IF all your interior doors were open and IF you still heard noise from the RETURN DUCTS, the noise could be transmision of the blower sounds caused by the layout of the ducts.
Again you should check this by removing the fan compartment door, opening all the interior doors and making note of the noise.
Make sure, as lynn comstock pointed out, that for safety you do not leave the door off. This could cause an unsafe condition.

If you still hear the noise from the RETURN DUCTS the ductwork may need changes that would require some custom modifications which would be better handled by a sheet metal contractor.

I would also suggest that you absolutely make sure that the noise is not also coming from the supply registers.
Again when you remove the furnace door and don't hear a marked change you should look at things other than velocity.

There is a lot of information here that should lead you to the source of the problem.
If it doesn't, I would suggest a reputable sheet metal or heating contractor be consulted.
You may have a simple problem that may be able to be solved in a matter of minutes, if someone were looking at it directly.

Good luck.
 
  #39  
Old 11-27-02, 12:33 PM
Heiko
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Thank you guys.
I am going to follow that advice.

I can sure say, I learned a lot.

Happy Thanks Giving.

and thanks again.
-Heiko
 
  #40  
Old 11-27-02, 09:19 PM
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the tonnage

of your unit is 3 tons, actually rated at 37,000 btus, the numbers underlined are the piston size. happy thanksgiving.
 
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