New gas furnace fan motor noise through the return

[MominTN]

I have a new HVAC 90 Plus high efficiency upflow gas furnace that was installed 3 days ago. It makes a high pitch noise that sounds like a very small hairdryer on high which I assume to be the fan blower. It starts up the same time as the fan so that must be it. It reaches a constant pitch and stays on as long as the fan is on. I have metal ductwork. The noise seems to be coming out of the return. You can hear it from every room on this floor but it doesn't seem to be coming out of the vents. You also can hear it in front of the gas furnace and in the basement in general.
They have tested every vent, the static, and other things, and decided to replace the blower today. The blower they took out was very hot so we were hoping that was it. The noise still is there.
I have read some of the posts on this forum that sound similar to mine, but I can't find where anyone came back to the forum and said what resolved this problem. If you know of a resolution, please reply.
Someone on this forum said to try this to someone else but I don't know if it worked.
http://www.ecoduct.com/forms/Flexible%20Duct/Duro%20Dyne%20Flexible%20Duct%20Connector.pdf
Surely other people have installed high efficiency units on metal ductwork and gotten rid of this air blower noise.

[clarkie]

If you don't have enough return air inlets ducted back to the furnace and possibly thru an undersized return air trunkline, this would produce a loud noise. Maybe you don't have enough return air?
Especially if is is an ECM fan motor!

[MominTN]

The return is 20" X 30" (size of filter). There is a plumbing pipe running down the middle. There is a square hole behind it as the house was constructed around this return. Looking down, it appears that the return ductwork does not come all the way across the bottom of this hole but maybe that is just the way the returns are suppose to look. They did open and look into the return. No one mentioned a problem with the return.
The furnace is 100K BTU for 13 ducts downstairs and a small duct in an upstairs closet. Downstairs is around 1721 sq ft.
Can a return be added in a wall? Or do you need to have more space?
They are now talking about some type of canvas connector.
I would really like to know how other people resolved a similar problem. I also am curious how many people are still using metal ductwork with the new high efficiency units and if they are quieter or noisier than the old ones.

[phbsales]

The noise you may be hearing as you described "a high pitch like a hairdryer" would be the draft inducer motor.

I'm also wondering, did your HVAC service provider do a load calculation on your home? I am a bit north of you and I plugged your square footage in to my own numbers in for my region, and I'm wondering if 100K btu is too big for your home. That could also present noise issues.

JMHO........

[beenthere]

What was the static when they tested it?

[MominTN]

What was the static when they tested it?

Don't know. They said it was okay.

All 5 estimates gave me prices for 100K btu. I had 125K btu on the old 21 yr old Heil.

[beenthere]

When they say its ok. And don't leave a record of it.
Well. They may not have checked it.

[wisconsinapp]

Its definately not any type of problem to have metal ductwork. I think that is probably the only CORRECT way to do it. Sure you could use other materials, but sheet metal is the best way to do it. I would have to agree and say its either your inducer motor, or not enough returns, a quick easy and not so right fix to that, would be to cut a register into your return drop in the basement, but that would be the installing companys problem, not yours.

[cook42]

I was wondering if when the furnace shuts off that if you hear a slight thump sound from your return duct if so I would check to see if the return duct is sized right.

And if that motor is hot like you say it sounds like to me that the motor is working hard to bring back return air to your unit.

I was always told that that the cfm that is deliverd to the space that the same amount must come back to the unit.

I would have them check the size of the return duct and also how many cfm's is being deliverd to your space.

[viessmann]

high pitch noise is coming from return grill or grills very common on new installs with 90%or higher try and remove grill to see if noise goes away i pretty much have to add extra return ducts and grilles to the retrofits i do in the old homes for what ever reason half the older homes never had any returns in the basements and when the dumbasses renovate the basements guess what they forget

[Pelican3]

I have two questions.

1. Did they do a temperature rise on your install? They might have recorded the results in the instalation manual. Check what they are and compare them to the rating plate on the furnace.

2. Does the furnace still make the noise when you pull the filter out? A lot of the expensive HEPA filters like 3M and others are very restrictive, resulting in high pitched noises as the blower sucks air in from around the base of the furnace as well as the filter door area. We recommend to our customers to buy the cheapest filter available, like the ones you can see through.

[clarkie]

That's a pretty bad info you are giving to your customers about buying the cheapest air filter available that you can see thru. I guess you don't mind about your customers recirculating the household dirt thru the HVAC equipment, clogging up the evaporator coil, blower wheel and motor, heat exchanger, ductwork, etc.
Come on man, a decent pleated air filter should be the least type of air filter recommended to a homeowner.

[Pelican3]

Is it bad advise? I really don't think that they contribute to clogged eveaporator coils. If you get your furnaced serviced yearly then buildup of dust on the blower motor and fan is not an issue. I find that the pleated filters cause more damage than what they are worth. They might be ok for day 1, but after that they are very restrictive and contribute to very high temperature rises, furnaces going off on limit, and cracked heat exchangers because of the high temperature. Don't be so quick to judge.

[jmcgreevey]

i agree with clarkie. if your furnaces are going off on high limit due to a pleated filter, most likely you are oversizing your systems. i would only expect to see a temperature rise increase of about 5 degrees maximum between a pleated and a see-through filter (a little more with a filtrete). besides, the price difference between a pleated and a see-through is about a dollar or two but it's protecting an expensive blower motor, keeping your air flow from being further restricted due to build up on fan blades and preventing there ever being a need to clean the evap coil or secondary heat exchanger.

[SalCange]

I don't think the noise is coming from the filter.. Small return drop. Should be at least 25x10 if it's not, just have a tech come out and lower the fan speed. Or it could be a small hole in the gasket between the inducer fan and the heat exchanger. Or a small hole in the heat exchanger. I know it's brand new, but you never know.

[MominTN]

They are replacing the furnace with a more expensive model, at no cost to me, with an ECM motor. They said the ecm motor is the quietest one. THe new one will be Rheem/Ruud, rgrm or ugrm.

The installation company says my size ductwork and my return size (20 X 30) is fine. There is no sucking sound at the return or sound from the vent grills. Just a high pitch motor sound from the air blower that comes up through my metal ductwork out of the return.

Hopefully the new ecm motor will be quieter.

[hvac-learning]

Very high pitch hum like a hair dryer? maybe inducer motor racked during shipping plastic housing and inducer wheel slightly rubbing? have the tech lift the inducer motor while it in the heat mode to see if it noise stops check the rubber isolater bushings

[Stamas]

Put your hand on the return air grill(s) and see if the noise changes or goes away. Sometime your hear the grill humming, resonate vibration.

[MominTN]

Put your hand on the return air grill(s) and see if the noise changes or goes away. Sometime your hear the grill humming, resonate vibration.

Took the grill off and the filter. Didn't change anything.

They are on their way to install the new model with the ECM motor. The regular motor for many people may be just fine. The new systems are extremely quiet. I just don't like the high pitch sound of the new fan motor. But one of the older men couldn't even hear it. So it may not sound the same way to all people.

So hopefully the ECM motor in the new model won't sound this way to me.

[docholiday]

If you have a duct issue, the noise will be worse with the ECM.

[mme121]

My new high-efficient, ecm motor furnace is also making a similar noise audible through the vents and within the furnace. It sounds like it's coming from the furnace not the ductwork. Will be calling the installers but it is very frustrating to have more noise than my 23 year old furnace had.

[docholiday]

so now address the duct issue

[MominTN]

I think any different sound that you are not used to is more noticable when there is metal ductwork. The Rheem/Ruud RGRM/UGRM model that they installed with the ECM motor seems to be alot quieter now, but they had to turn down the blower with DIP settings. The factory settings caused it to sound a little bit like the other one and even stronger air thru the vents. But I believe that there are more settings with the ECM motor and they turned it down twice before I could no longer hear it. The house warms up quickly and I never hear it on. Not sure if the blower setting will be correct for A/C but for now I'm satisfied.

[WhoIsThat?]

I just don't like the high pitch sound of the new fan motor. But one of the older men couldn't even hear it. So it may not sound the same way to all people.
Women keep their high frequency hearing longer than men.
http://www.agingsociety.org/agingsociety/pdf/hearing.pdf
http://www.womenshealthresearch.org/site/News2?page=NewsArticle&id=5372&news_iv_ctrl=0&abbr=press_

[pfeifer]

without more info. i cant say for sure but if the ductwork (return) is of proper size you can insulate the inside to reduce and muffle the noise but I bet you will find the return needs added to. The canvas you heard mentioned is probally a vibration eliminator and may not help you unless it is the duct vibrating from the blower

[mike dixon]

just live with it

[mme121]

What great advice. You must be a pro.

[MominTN]

The return is 20 x 30. When you take off the cover, there is a large square hole behind the cover down to the return. The HVAC installer said that there was plenty of room for the air to mix up.

The sound does not just come from the return. It also comes from the vents. And sound does not always come through the very same vents. Sometimes you hear it standing in the middle of the room. So isolating any source of sound isn't easy.

Now I have model UGRM with the ECM motor which has been turned down. (First they installed the UGRL.) I am happier with this last one. The sound isn't as high pitched as the other one which sounded like a tea kettle that is ready. I did not notice any difference after they installed the canvas at all so I think that was a waste of their time.

If I decide for them to turn up the blower, I'm going to get some of my ductwork replaced with flexible ductwork. I never wanted it before but it is alot quieter so if I were building a new house, that is the way I would go. I have two new flexible vents that are as quiet as can be. The noise does not travel through them. If I had replaced some of my ductwork with the first one they installed (UGRL), then it would only have made the sound at the return. I am so glad I have no returns in living areas.

And I would never replace an HVAC that I was happy with with a newer model unless it was cost prohibitive to fix and keep. My mom's gas furnace is over 30 yrs old and she gets good heat that you never hear. The furnaces now aren't built to last over 15 years.

About the ideas on insulating the ductwork, where does the insulation go?

[commerce48]

just live with it

Hopefully you are not a pro. If you are, this helps to point out major problems with the HVAC industry. The perception I am getting from reading about HO experiences finding qualified professionals, reading some professional's posts here, and my own experience with getting quotes for a furnace replacement is that most are hacks. In my case only one out of 15 even bothered to do a Manual J - this included the largest companies in my area, personal referrals, and random installers from the phone book or manufacturer's site.

It certainly looks like when you find someone good, you have to latch onto them forever, no matter what equipment they sell because the chances of finding someone else is so slim.

The system looks completely broken to me. No industry is composed of 100 percent competent professionals, but the ratio of good professionals in the HVAC industry appears to be exceptionally low. HO have pretty poor odds, and techs have job security.

[ChicagoJim]

I have the same problem too with my 3 day old furnace with ECM motor.

I just replaced my 21 year old York with 1600 cfm AC motor with a Lennox G61MPV-060C-111 furnace with ECM DC motor.

The new Lennox at 1365cfm (1st stage heat) and 1525cfm (2nd stage heat) is louder than the old York AC at 1600cfm.

I fought the installer to put in a 12x24 drop return duct (they wanted to do just one 8x24 or 10x24) and a 20x25x1 filter (they wanted to do smaller 16x25x1 which was easier metal fabrication). I originally had two (2) 8x24 drop returns.

Since the filter they installed is a non-pleated one that you can see through, I'm wondering if a high-quality pleated filter (with a thicker filtering medium) may muffle the motor noise.

Earlier in this thread, an induction fan motor noise was raised as a possibility... Lennox customer service doesn't think that the induction fan is the problem since the induction fan is isolated.

Perhaps I will add some additional return ducts too... I can always close them off if that doesn't address the problem.

EDIT: PS... In the summer, are A/C fan speeds supposed to be higher than winter heating fan speeds? If so, my fan noise issue may be a bigger problem in the summer running the A/C.

[commerce48]

Motors do not need to be in the air pathway to transmit noise/vibration (think about AC compressors for example). That said, isolation of the air pathway counts. So a thicker filter may reduce retrograde transmission via the returns, but have no effect (unless the restriction increases motor noise) on supply vent noise.

Yes, AC use is generally at a higher CFM, however if the inducer motor is the cause of noise in the heating cycle...

[ChicagoJim]

I just reduced the ECM motor whine a lot (it's now very low) by replacing the non-pleated fiberglass filter with a relatively cheap pleated TrueBlue Merv 7 filter.

I don't think the thicker filter medium restricted air flow performance because there is still a "thud" from the return duct buckling when the fan turns off.

[commerce48]

I just reduced the ECM motor whine a lot (it's now very low) by replacing the non-pleated fiberglass filter with a relatively cheap pleated TrueBlue Merv 7 filter.

I don't think the thicker filter medium restricted air flow performance because there is still a "thud" from the return duct buckling when the fan turns off.

What you did was increase the motor load which apparently changed its resonant frequency. Yes, you did restrict air flow, for which the ECM blower was able to compensate. Not sure what you mean by "performance". Energy consumption increased, and efficiency and system lifespan dropped.

[ChicagoJim]

What you did was increase the motor load which apparently changed its resonant frequency. Yes, you did restrict air flow, for which the ECM blower was able to compensate. Not sure what you mean by "performance". Energy consumption increased, and efficiency and system lifespan dropped.

What I hear you saying is that my new furnace's lifespan has dropped because I'm not using the 99 cent non-pleated/see-thru filter the HVAC contractor provided.

That is, the $2.50 pleated Merv 7 TrueBlue filter is going to ruin my variable speed DC motor.

All of the six contractors that bid on the job bid to have a smaller filter installed (around 16x25). I the unknowledgeable homeowner insisted that a 20x25 filter be installed.

I guess this homeowner knew better than the professionals that putting a larger filter would improve performance and allow a really cheap pleated filter be used in lieu of the 99cent crap filter the "professional" was going to install.

WHile your deduction is logical, I find it hard to believe that Lennox is going to let a $2.50 pleated Merv 7 filter shorten the lifespan of its 110btu variable speed system at medium low fan speed (~1500 cfm) when the system is designed to operate in this exact same configuration (i.e., single side return with 20x25 filter and field fabricated transition) that is designed to operate at upto 2135cfm.

EDIT: Sorry if I came across harsh.
I had a bad experience with my installation despite the HVAC company being having received special dealer recognition by Lennox and York. Among the issues:
1) Installer fried the Aprilaire circuit board when shorting the outlet to determine which fuse controlled the furnace (I verified this by doing a continuity test on individual humidifier circuit board components).
2) I had to correct the the 1 stage AC compressor wiring to the t-stat (it was wired to Y2 on the t-stat)
3) Failed to follow Lennox instructions to limit exhaust and intake 2" PVC vertical length to max 2" and 4" respectively prior to transition to 3" PVC (23" of 2" vertical PVC was installed on intake and exhaust).
4) I had to explain that the IAQ t-stat can control the humidifier by hooking up HUM1 & HUM2
5) I had to explain that the IAQ setup needs to be reviewed and corrected because its AUTODISCOVERY set it up as: 1-stage heat for my 2 stage furnace, 5 cph heat (meant for <90% furnaces) not 3 cph for my 95% furnace.
6) I had to direct the installer to change the DIP switch setting so that my IAQ T-stat controls 2nd stage heat and not the furnace (why else pay $$$ for an IAQ if it's not going to control stage 2?)
7) I had to explain that there was a installer setup tests on the IAQ to validate system setup. When the A/C compressor test ultimately failed due to issue #2 above, I should have insisted they hang around and diagnose and not leave at 4pm.

If I hadn't read the furance installation manual (1 hour) and IAQ installation manual (1 hour), I would not have received the advance functionality I was paying for in the IAQ and 2 stage furnace. This makes me wonder how many other homeowners have received substandard installation, but are completely unaware. Caveat Emptor.

[MominTN]

Where does duct insulation go?

[commerce48]

Never any harm in upsizing returns as far as I know. However with a 1 inch pleated filter, you have effectively accomplished the opposite. At around 500 CFM, the pleated filter has a static drop of about 50 percent more than the fiberglass. I don't have a full curve but I believe it is about double the static drop at 1,000 CFM and goes up from there. That's with clean filters.

If you want the higher MERV rating such as a 7, you should go for a 4 or 5 inch media filter. Then the static drop is similar to a 1 inch pleated. Do it for only air quality reasons, not furnace protection.

For furnace protection, that fiberglass filter will do a better job generally than a 1 inch pleated. Besides the factors I mentioned in my prior post, when you raise the static drop across a filter, air often finds a way around the filter instead unless it is very well sealed, thus actually increasing dirt accumulation in your furnace and coil. Most one inch filter stacks are very poorly sealed.

There is a reason why manufacturers spec either a one inch fiberglass or a media filter. When I bought my first house last year and shopped filters, I made the same intuitive mistake you made. How could a filter you can see through be better than even the cheapest pleated? If you peruse the many threads about filters here, you will read that many problems including early failure from dirt buildup were caused primarily by 1 inch pleated filters.

[ChicagoJim]

I suspect the static pressure bottleneck in my system is still with my return ducts prior to the drop return and not with the pleated filter.

Why? Despite the Merv 7 pleated filter, the oversized drop return I had installed still collapses (sides suck-in) when the fan is on (and "thuds"/releases when the fan turns off).


I should add returns to this house we just bought 6 months ago (so I can run the fan on med-low with out return duct buckling) -- preferrably in places with limited returns (2nd floor master bedroom- one return for four supplies in bed/bath suite) and no returns (kitchen/mud room - no returns for 5 supplies).

Unfortunately, it's going to be a PITA to add a second floor return.

[commerce48]

Interesting instrumentation! You may well have bigger static issues elsewhere, but in no way is a one inch pleated filter beneficial.

[gravity]

sounds like ductwork issue to me. make sure theres no foil tape in the return....it can make an annoying sound...had to take off a grille and climb in the ductwork to find that someone put tape inside the return....could be worth looking for!

[docholiday]

You would not want to add returns to the kitchen or bathrooms. There are odors in both of them that your family would appreciate you leaving in those rooms.

I would suggest before doing any modifications, actual measurements be used. I personally would look at velocity to see where the problem is.

[ChicagoJim]

You would not want to add returns to the kitchen or bathrooms. There are odors in both of them that your family would appreciate you leaving in those rooms.

I would suggest before doing any modifications, actual measurements be used. I personally would look at velocity to see where the problem is.

Thanks for the reply.
I was thinking of additional returns in the bedroom and dining area of kitchen.

I know about keeping returns out of bathrooms. :stinks: