# reducing noise with goodman furnace



## cliftonian (Mar 4, 2012)

I have a small house (1100 sq ft) with a 95 % efficiency Goodman unit. The return air register makes quite a noise in the house. Lower blower speed is fine for me. So, without knowing that return duct noise has anything to do with blower speed, is it a good idea to reduce the blower speed of the furnace? Photo of existing wiring is attached. Thanks..


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## Plumber101 (Feb 25, 2009)

No it is not.

With this said the reason is that lowering the blower speed will raise temp rise and that can cause the high limit to trip causing another issue.

Best to determine what is causing the noise. Return undersized, loose metal flapping, filter dirty ect

If you measure supply temp and return temp and sub-tract return from supply this will be your temp rise.


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## yuri (Nov 29, 2008)

Change the register to a plastic or wood one and it will be a lot quieter. Metal ones can sing. HDepot has some.


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## ben's plumbing (Oct 6, 2011)

remove one return register at a time till you find the one that likes to sing...:yes:


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## Jackofall1 (Dec 5, 2010)

When you say, "The return air", do you mean that you only have one?

If this is the case there is a good chance you don't have enough net free area and the velocity going through the RA is too high.

With that said it sounds like you need to add some area by increasing the number of RA openings.

Mark


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## how (Feb 26, 2011)

If the noice is from a harmonic vibration by the return air grill, then just place your hand against the grill the next time you hear this noice. If the noice lessens or stops then its sympathetic grill vibrations. If it's a metal fined grill then changing the angle of every second fin by 20 degrees with needle nose plyers will help. Wood grills create less harmonic noice but the blocky ones are often more restrictive to the air flow.
A temp rise test on the furnace is the usual test that a tech will do when dealing with a noicy return grill to determine the difference between symtom and cause.


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## paul52446m (Jan 8, 2012)

cliftonian said:


> I have a small house (1100 sq ft) with a 95 % efficiency Goodman unit. The return air register makes quite a noise in the house. Lower blower speed is fine for me. So, without knowing that return duct noise has anything to do with blower speed, is it a good idea to reduce the blower speed of the furnace? Photo of existing wiring is attached. Thanks..


In a 1100 sq. ft. house you don't need to move that much air. I would try putting the red wire on the heat post, and then check the heat difference across the in and out of the furnace, What model do you have? How much 
cooling do you have on the furnace? Paul


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## beenthere (Oct 11, 2008)

Post full model number of the furnace. Your house may not need as much air as the furnace is moving, but the furnace may need to move that much air.

The full model number will be in the burner compartment.


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## Plumber101 (Feb 25, 2009)

paul52446m said:


> In a 1100 sq. ft. house you don't need to move that much air. I would try putting the red wire on the heat post, and then check the heat difference across the in and out of the furnace, What model do you have? How much
> cooling do you have on the furnace? Paul


Please don't make any changes to the furnace as the above poster has suggested. You have a two stage heat furnace and without understanding low heat and high heat settings don't start making changes. If you start making fan speed changes and increase the temp rise without checking Delta T on both low and high heat and making sure the high limit is working these changes could be devastating.


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## plummen (Jan 10, 2010)

If its in heating mode it should already be on its lowest speed setting.
Are your returns in the house blocked by anything?


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## Plumber101 (Feb 25, 2009)

plummen said:


> If its in heating mode it should already be on its lowest speed setting.
> Are your returns in the house blocked by anything?


But it's not

From the pic

Cool tap Black wire HI Speed
High heat tap Orange wire Medium high speed
Low heat tap Blue wire Medium low speed
Park tap Red wire Low speed


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## cliftonian (Mar 4, 2012)

thank you all for your posts. in response to the questions raised:

- the unit model # GMH95070BXA
- there is only one return air register and it is located in the hallway.


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## cliftonian (Mar 4, 2012)

and it is only furnace; no air conditioner is connected.


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## ben's plumbing (Oct 6, 2011)

cliftonian said:


> thank you all for your posts. in response to the questions raised:
> 
> - the unit model # GMH95070BXA
> - there is only one return air register and it is located in the hallway.


 how big isit......16 x25,,,16 x 20...20 x 20..


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## cliftonian (Mar 4, 2012)

it is 20 x 20.


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## Jackofall1 (Dec 5, 2010)

ben's plumbing said:


> how big isit......16 x25,,,16 x 20...20 x 20..


Don't think that the size of the grill matters at this point, based on the unit model and assuming .5" external pressure its moving (or try to move) about 1000 cfm (on MED speed) through (1) grill. The stud cavity doesn't have enough free area to be used as a singular return. Must add some RA capacity in my opinion.

You have a total of 2 ft2 of grill going into about .5 ft2 of stud cavity where you need approximately 2 Ft2 of duct/stud cavity to maintain an acceptable air velocity.

Mark


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## beenthere (Oct 11, 2008)

20X20 filter grille is good for about 570 CFM at a face velocity of 300 FPM, and about 960 CFM at 500 FPM.

At a 70° rise it needs 879 CFM, for a 50° rise it needs 1,120 CFM.


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## Jackofall1 (Dec 5, 2010)

beenthere said:


> 20X20 filter grille is good for about 570 CFM at a face velocity of 300 FPM, and about 960 CFM at 500 FPM.
> 
> At a 70° rise it needs 879 CFM, for a 50° rise it needs 1,120 CFM.


Thats all fine an dandy, but if this RA is going into a stud cavity the velocities would be upward of 1500 FPM resulting is too high of a delta P diminishing the volume dramically.

We need to know where the RA is.
Mark


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## ben's plumbing (Oct 6, 2011)

Jackofall1 said:


> Thats all fine an dandy, but if this RA is going into a stud cavity the velocities would be upward of 1500 FPM resulting is too high of a delta P diminishing the volume dramically.
> 
> We need to know where the RA is.
> Mark


 see alot down south..20 x20 filter box with 12 or 14" flex hooked to it... framed in hallway..


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## Jackofall1 (Dec 5, 2010)

ben's plumbing said:


> see alot down south..20 x20 filter box with 12 or 14" flex hooked to it... framed in hallway..


Yes this is what I am thinking now, I haven't seen much of that around here, RA are usually in stud cavities.


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## ben's plumbing (Oct 6, 2011)

Jackofall1 said:


> Yes this is what I am thinking now, I haven't seen much of that around here, RA are usually in stud cavities.


 yea my thougth too... but many are now just installing filter box with flex duct connected to back...had one last week where 3m pleated filter was colasped into the duct from dirt....12" round return..


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## Jackofall1 (Dec 5, 2010)

I imagine you see all kinds of neglect, folks think that they turn it on and it runs, that is until it doesn't run any more. 

Then they call the fix-it man

and then they post on a DIY web site, like, is this too much to pay for a 

service call.......

I can't imagine working in the service industry, what you guys see and hear on a regular basis would make a grown man cry, I am sure.

Mark


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## ben's plumbing (Oct 6, 2011)

Jackofall1 said:


> I imagine you see all kinds of neglect, folks think that you turn it on and it runs, that is until it doesn't run any more.
> 
> Then you call the fix-it man
> 
> ...


 yes Iam crying now just got off the phone with a no heat took me 15 min to explain how to turn off switch for furnace that I painted RED for her 2yrs ago...:laughing:


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## hvac5646 (May 1, 2011)

Did 'ya use the old "light Switch"
analogy?


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