Furnace is making a "winding down" sound at the end of the cycle


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Old 05-14-22, 11:08 PM
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Furnace is making a "winding down" sound at the end of the cycle

I have a 25 year old gas heater. At the end of the heating cycle, instead of just stopping making all of its noises, with only the fan continuing for a minute or so blowing out the lingering heat, it's making what I can only describe as a winding down sound, like something is running slower and slower and then stopping, rather than just stopping. It's not loud, it's far too deep to be described as a whining, there's no banging or other noises associated with this, and there are no other visible problems at this time. I've used every synonym and phrase I can think of looking for articles about this sound, but no dice so far. Does anyone have any ideas?
 
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Old 05-15-22, 04:30 AM
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Hi, can you post a video so that we can here the sound?
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Old 05-16-22, 11:26 PM
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My husband is reluctant to move furniture to get to the heater in the hopes that he MIGHT be able to capture a sound… What are my choices for sounds that occur ONLY when the heater goes off, and aren't split-second sounds like a bang or a pop? :-)
 
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Old 05-24-22, 12:13 AM
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Seriously? I have the only heater in the history of the world that's making a drawn-out sound at the end of its running cycle? No one has even the wildest guess as to what it might be, or what parts within a heater are even capable of making a noise when the heater shuts off?
 
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Old 05-24-22, 12:23 AM
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Since it has a fan we can assume this is a furnace. It's posted in the boiler forum.

If the winding down noise is heard when the burner shuts down but the main blower is still running.... it could be a defective draft inducer blower motor.
 
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Old 05-24-22, 01:00 AM
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Sorry if I somehow ended up in the wrong sub-forum… Is there a way to move the thread, or should I try reposting it?

The noise only occurs at the end of the heater's cycle, in other words it's not coming on multiple times when the gas flame goes on and off. There is still air running from some source for a minute or two after the heater shuts down, and it's during this time that the dragging sound occurs. I've looked up the draft inducer blower motor, and the articles describe sounds that occur throughout the time it's running, not just at the end, and not anything like the sound I'm hearing; can you give me any hint as to what you think it might be, or what other part of the heater is also running during this time and could also make noises? Thanks!
 
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Old 05-24-22, 04:53 AM
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We donít know what type of heater your dealing with, mfg. model # may be helpful.
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Old 05-24-22, 07:29 AM
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Do the parts that could still be moving to make a noise after the heater shuts off vary so wildly between manufacturers and models? I know that it's an old Rheem, at least 25 years old. I don't have any model information, and before you ask, I'm not capable of doing the furniture moving necessary to open up the heater cabinet and look for anything. I'd be thrilled to get names for any parts that could be making a dragged out sound, so I have some terms to look up and see if some website describes this situation! My guess is that it's something that's spinning, because it sounds like if you turn off a record player while the needle is still on the record, and the music is playing slower and slower.
 
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Old 05-24-22, 01:48 PM
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Thread moved.

Ok.... so it's not the draft inducer. That leaves the main blower.

There can be a direct drive motor with a squirrel cage blower.
The motor bearings could be going bad or something can be lodged in the blower wheel.

There are also belt driven blowers that have a belt that can make noise as well as the motor or the blower bearings.
 
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Old 05-24-22, 08:50 PM
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Thanks for the ideas! I looked them up, and here's what I found:

If the motor bearings are going bad, they make a high-pitched squealing or shrieking noise, which is kind of the opposite of what I'm getting, and my noise is only for a few moments at the end, not all the time as this sound is described to be. They can also make a rattling sound if the motor mount is loose, which again, is the wrong sound and would be happening constantly.

A squirrel cage blower can also make a loud grinding sound while it is running, which also doesn't apply here.

I don't know if my heater is old enough to have a belt, but if it does, a loose or damaged belt also makes a screeching or squealing sound, and also throughout the time the heater is running, not just at the end.

The blower wheel also makes a high pitched noise if it has a problem, and throughout the time that the heater is running, not just at the end.

Bad blower bearings also caused a squealing, or a thumping instead of the rattling the other bearings make, and also throughout the running of the heater, not just at the end.

So, all of those parts can make noises, but the noises they make are nothing like the DEEP dragging noise that I described. And, all of these noises would happen the whole time the heater is running... not only AFTER the heater has shut off, like the noise I described.

Having looked through a bunch more articles on heater noises in search of the above info, I still haven't identified a single noise that only occurs when the heater goes OFF, or that sounds anything like the deep continuous noise that I'm getting. Is it possible that some old sound insulation somewhere has crumbled, and the sound that something makes as it's spinning down... and anything that spins would spin down when turned off, right?... is now audible when it wasn't before?
 
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Old 05-25-22, 09:07 AM
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If your furnace uses a variable speed ECM motor for the blower, I think that could explain why you hear noise for minutes upon shutdown. Here is an excerpt from an article about their use in air handlers, but I think it would be the same for a furnace. (I pretty sure Rheem uses variable speed ECM motors in some of their furnaces).

The air handler will turn on and ramp to 50% (or whatever percentage the manufacturer deems appropriate) and then after so many minutes as determined by the program the ECM blower will ramp to 100%. When the thermostat satisfies the motor will slowly ramp down and then stop after so many minutes. This is often referred to as soft start and soft stop.

https://highperformancehvac.com/vari...ge-ecm-motors/


 
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Old 05-25-22, 12:21 PM
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There won't be an ECM motor on a 25 year old furnace.

You're going to have to investigate inside the unit.
We've pretty much used up all our guesses.
 
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Old 05-25-22, 02:46 PM
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@Pj-

OK I see Ė I thought I read that they have been in use for at least 20 years, and I guessed that possibly Rheem may have been on the bleeding edge at that time Ė and/or maybe the 25 year estimate was off by a decade or so. (like my estimates - Iím really bad at estimates of time that has passed Ė lol!).

Just sounded suspiciously like some kind of extended and intelligently controlled shutdown. Is it possible that the furnace was updated with an variable ECM motor? I see that some contractors push that. But I don't know which - if any - of those ECM's would even be designed with multi-minute shutdown potential. Just a guess.

But I guess as you say, more info must be provided. Too bad.
 
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Old 05-25-22, 09:25 PM
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I think I know which heater I have now! I was able to badger my husband into digging out the box with all the house related stuff, and, although it has the installation and purchase paperwork for everything EXCEPT the heater, naturally, mixed in with a mountain of stuff about our Rheem air conditioner was glossy brochure about a heater that I'm pretty sure is the model I have:

Rheem Criterion II

Does that provide any useful info?

And just as a sidenote: That ECM motor is the only heater thing I've heard about so far that wouldn't make a noise throughout the running of the heater; thanks for tossing that out! This article from 2010 says that ECM motors had been used for over 20 years in the HVACR industry at that time, which would take us back to before 1990:

https://www.rses.org/assets/servicea...l/ECM1_web.pdf

Various other articles name 1987 as the magic year.
 
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Old 05-26-22, 09:05 AM
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If you use the first link below as a starting point, it looks like the Criterion II is a pretty old line, and if you look at the parts lists for the various models, it looks like they donít use one of those fancy schmancy variable ECM motors. Bummer! And some Criterion II parts are not even available at this time.

Is it possible that someone updated the motor? I donít know how likely that is. Seems like a stretch I guess. I think Pjmax would know the likelihood of that.

https://thedailythrive.org/rheem-cri...nace-overview/

This link describes how to read Rheem Model numbers.

https://thedailythrive.org/how-to-re...model-numbers/

It sounds like you already knew this information but here it is anyway:

https://thedailythrive.org/rheem-fur...lacement-cost/

I havenít lived in a place with a furnace for 20 years, and even then I didnít maintain it, so I am no expert for sure. But maybe itís just time for a new motor Ė but those are really expensive. I had no idea.

If it were me Iíd see if I could inspect the blower wheel as was previously mentioned and also clean any filters that are accessible.

 
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Old 05-26-22, 11:14 PM
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Unless someone snuck in while I was sleeping and updated my heater, lol, then no, it hasn't been updated… But more importantly, this is a NEW noise that the heater is making, not something it's been doing all along as an ECM motor would be doing.

I did thorough research about all the mentioned parts that could be going wrong, and as posted above, these parts make high-pitched screeching or squealing noises when they're going bad, not a deep noise like I'm hearing, and it would make the noise the whole time the heater was running, not just after it turned off.

I still haven't found a single article that mentions ANY noise that would just happen after the heater turned off, or that makes anything like this slow dragging-out sound…?
 
 

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