Furnace squeaks when it turns off

[Mark P Williams]

Hi,

First time poster...

I'm fairly new to the US forced air furnace system, but my question is something that I haven't gotten an answer to on google... so here I am.

My furnace appears to be functioning normally, no strange sound except when it finishes and the thermostat clicks off... when the airflow stops there is a horrid squeak, followed by another squeak and then a third... this has been happening for quite sometime, with this being the third winter in the house in the north east but to my ear it is getting longer.

If this is normal and is just the sound of a vent closing, that would be awesome but I'd like to check!

also the thermostat clicks off and the furnace takes a minute to shut off... it is a high efficiency furnace installed in 02.

Much appreciation to anyone out there who has a clue to what this could be.

Thanks,

Mark.

[The Daring Dufas]

POSTING VIRGIN! EVERYBODY PILE ON! ^_^

TDD

[mike]

lube the flappers in the bathroom and kitchen vents. BUT if the flappers are being blown open by the furnace, you've got a lot of wasted heat that needs to be tracked down and fixed...like a leak in the suction side of the furnace.

[DerbyDad03]

The easy answer is for question 2: the reason the furnace takes a minute to turn off is to allow the fan to remove the remaining heat from the heat exchanger both so that it isn't wasted and so that the heat exchanger cools down more evenly. That helps the heat exchanger last longer.

As far as the squeak, have you tried having someone turn the fan on and then off as you listen to first the blower itself, then some of the ductwork/vents to see if you can isolate the noise? It sounds to me like the blower may need some lubrication, but that's hard to tell from where I'm sitting.

There should be a switch on the thermostat that says Auto and On. Switching it to On should turn the fan on even if the thermostat isn't calling for heat. You can use that to turn the fan On and Off by setting thermostat to a low temperature. Since the furnace won't call for heat, Auto will be the same as Off and On will be, well, On.

You should be able to isolate it if it happens every time the blower turns off. By the way...No, it's not "normal".

[Stormin Mormon]

Maybe blower drive belt needs replacing?

Christopher A. Young Learn more about Jesus

.

Hi,

First time poster...

I'm fairly new to the US forced air furnace system, but my question is something that I haven't gotten an answer to on google... so here I am.

My furnace appears to be functioning normally, no strange sound except when it finishes and the thermostat clicks off... when the airflow stops there is a horrid squeak, followed by another squeak and then a third... this has been happening for quite sometime, with this being the third winter in the house in the north east but to my ear it is getting longer.

If this is normal and is just the sound of a vent closing, that would be awesome but I'd like to check!

also the thermostat clicks off and the furnace takes a minute to shut off... it is a high efficiency furnace installed in 02.

Much appreciation to anyone out there who has a clue to what this could be.

Thanks,

Mark.

[Ed Pawlowski]

Could be that the damper just needs a squirt of lube on the hinges.

A lesser possibility is that something is rubbing as the furnace cools down and the metal contracts.

The blower runs after the T-stat shuts off to utilize any heat left in the heat exchanger. This adds to the overall efficiency as it is blown into the house and does not escape to the outside vent or chimney if there is one.

[clare]

The shut-down delay is normal - the fan stays running untill the heat exchanger sheds the majority of it's heat.

I suspect you have a direct drive fan, judging by the age. I'd be suspicious you MAY have a bearing or bushing problem. Should not be hard to determine with a bit of sleuthing.

[krw]

Hmm, a gang flame?

[The Daring Dufas]

No, initiation. We have to make him crawl around on all fours, eat worms, bark like a dog then take a paddling. Then he can join the fraternity. ^_^

TDD

[homeowner]

The blower should be lubricated on all furnaces at least on a year. It dont sound like you have done this. Just begin by lubricating the blower and the blower motor. Normally 3 to 6 drops of a light oil in each bearing. (Some modern motors do not have oil holes. They are supposed to be lubricated for life). If the blower has a V-belt (fan belt), that could squeak too.

Lube it, then watch the blower while someone shuts off the furnace.

[nestork]

Personally, I wouldn't lubricate anything until I found out what was squeeking.

The way you pinpoint the source of noises in machinery is with an inexpensive tool (typically $15 to $20) called a "mechanic's stethoscope" which you can buy at any place that specializes in automotive mechanic's tools:

[image:

You simply touch the metal probe of the stethoscope against any part you suspect of making noise, and the closer the probe is touched to the source of the noise, the louder the noise will be heard through the earphones. In this way, you can quickly and easily pinpoint the source of noises in all kinds of machinery, and that includes finding out where that squeek is coming from in your furnace.

I have a $15 Lisle mechanic's stethoscope that I've been using for over

20 years to find the sources of noises in the machinery in my apartment block, like the washing machines and clothes dryers. For a cheap tool, it works surprisingly well.

[Stormin Mormon]

I've hosted many such initiations. After a while, I earned the exalted title of "Top Posting Moron".

Christopher A. Young Learn more about Jesus

.

No, initiation. We have to make him crawl around on all fours, eat worms, bark like a dog then take a paddling. Then he can join the fraternity. ^_^

TDD

[Art Todesco]

Agree to the damper thing. On my unit, I have a zone controller, now with

3 zones. With the everything off, all 3 zone dampers are wide open. When 1 zone calls, the other 2 will close. At the end of the cycle, those 2 zone dampers will again open. They are electrically held open and when 24 volts is removed, the damper closes via some type of spring return.

[Jim Elbrecht]

-snip-

Here is what should be the sequence of events;

1. thermostat shuts off;- you might hear a click [from the thermostat]
2. burner finishes cycle- when it stops you should just hear the pump and 'fire' stop.
3. The fan will continue to run until the plenum reaches a pre-set temp. When the fan stops, if all is well, you'll hear nothing. if the fan stops with a squeak, then you might have a belt driven fan that needs tightening/replacing.

Jim

[DerbyDad03]

Wouldn't the fan belt squeak on startup, not shut down?

I'm thinking of the squeal that a loose automobile fan belt makes as a car accelerates. It doesn't squeal once you reach a steady state speed or when you take your foot off the gas because it's not going to slip as it slows down.

Wouldn't the same thing occur in a furnace - slippage on startup but no more torque (?) once the motor shuts down, therefore no squeal.

[Stormin Mormon]

I've noted more fan belt squeak on start up. Motor comes to life, but the blower fan still standing still.

Christopher A. Young Learn more about Jesus

.

Wouldn't the fan belt squeak on startup, not shut down?

I'm thinking of the squeal that a loose automobile fan belt makes as a car accelerates. It doesn't squeal once you reach a steady state speed or when you take your foot off the gas because it's not going to slip as it slows down.

Wouldn't the same thing occur in a furnace - slippage on startup but no more torque (?) once the motor shuts down, therefore no squeal.

[Jim Elbrecht]

-snip-

You might be right. It has been a long time since I had that squeak. Jim

[hrhofmann]

The squeek may occur only in a certain range of speeds. On start-up, the motor/fan goes thru that speed range very quickly, so no squeek. On shut-down, the fan/motor coasts down relatively slowly, spending more time in the speed range where there is a squeek. So you hear it only on shut-down, not on start-up.

I agree to not oiling until noise is located, but oiling once a year is a very good practice to save bearings and $$$.

[dennisgauge]

Not normal.

Also not rocket science to run over to the furnace, stand there and LISTEN = to see if you can narrow down the source of the sound.

You should also consider calling a professional. An experienced reputable p= rofessional has certainly seen this exact problem before and should have a = pretty good idea what the problem probably is without even hearing the nois= e or looking at the unit. All he'll need to know is the model of the unit a= nd the circumstances under which the noise happens.

[clare]

On my old belt drive 2 speed furnace fan the belt chirped every time the fan swirched from high (heat or cool) to low (standby circulation) and not when starting. The inertia of the spinning fan was higher than the accereation torque of the motor. Switching to low was like slamming the brakes.