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The blower of my furnace makes a loud noise every time it starts. I understand that a large fan and the movement of large amounts of air will produce some noise. What I am puzzled by is the noise that sounds like a "starter." The noise only lasts for about a second or two; then there is just the expected sound of blowing air.

Could it be a motor failure problem at its infancy, or could it be related to the capacitor start on the motor? The blower pushes air without a hitch. Is this a normal condition that is heard on all blower motors?

Additional details:

My system is a direct drive motor driven, "squirrel cage" type fan, hot air, oil fired furnace. I am aware of the sounds of the fuel pump and then ignition of oil rumbling in the fire box (I don't know if that's the right term) but anyway the sound that I am trying to troubleshoot is the noise when the fan motor starts (my best description is that of a car starter) It may be spelled RRen-nen-nen-nen and then just the sound of moving air after the fan gets to full speed. There is a capacitor on the motor, could it be a malfunctioning capacitor? I have lived in an apartment building for 30 years and now in a single family dwelling, and have never heard any heating system noises. My concern is in what to replace; motor & capacitor, or just motor, or just capacitor or is that just a noise that I am going to have to get used to?

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    Could you describe the sound better? A click click, a tick tock, a wirr, a whine, etc.
    – Tester101
    Commented Dec 25, 2011 at 13:26
  • What type of fan/motor combination do you have: direct drive or belt?
    – RSMoser
    Commented Dec 29, 2011 at 21:13

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+25

Maybe you have a belt that is slipping. It might make noise until the blower starts spinning. It you have a belt, check the tension.

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  • If you cannot increase the tension, then you will need to replace the belt.
    – RSMoser
    Commented Dec 29, 2011 at 21:14
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The controller circuit for your furnace (usually a little box to the right of the motor with lights, a reset button, and some wires connected to terminals) is responsible for the operation of your furnace. It handles the motor that pumps air and oil, the flame sensor inside the unit, and the ignitor.

The ignitor is a gap between two metal poles and runs at high voltage in order to create a spark between the poles (and thus plenty of heat).

The order that things start up (motor or ignitor first) varies between controllers. Either way, the first few seconds of operation involve the motor and the ignitor running until the fire starts or the controller decides it has been potentially spraying flammable liquids for too long without seeing a fire.

It's likely in your case that the ignitor is running, then the blower. The blower is louder. I've had controllers that run the ignitor before the blower and after the blower.

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What type of fuel does your furnace use? I have an oil burning furnace, and when the oil first ignites, there is a "whomp" noise from the sudden expansion of gasses in the burner box. This happens at the same time that the blower motor turns on, and could easily be mistaken for coming from the blower or motor.

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Your problem is likely a failing -- though not entirely failed -- start capacitor. I had one of these going bad on our RV air conditioning unit. Every time the blower would start up, it would make a somewhat loud oscillating humming sound -- yeah, kind of like a starter motor. I thought that was normal, not having anything to compare it to. Then one day, the blower failed to start. I opened up the housing and heard the motor just sitting there humming but not turning. I took a long tool and started the blower turning, and it took off, turning at normal speed. I knew then the capacitor was bad. Ordered a new one, carefully replaced it (they can still give you a nasty shock even when the power is turned off). Now the blower motor started with a quick whoosh -- no humming.

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Your problem is the blower motor, The noise is the bearings, I would also replace the Cap if the uf reading is more than 5% low, if you don't have a meter then just replace the Capacitor as the bad motor has more than likely damaged the existing cap due to the extra load the motor has put on it. (A cap for that size motor should not cost more than $20) I don't know why some of these crackers are asking you about checking the belt and such, when you state its direct drive... If Your cap was the only issue the motor would make a buzzing sound and not start.

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    The OP mentioned that the noise was only when the blower starts. Wouldn't failing bearings likely make noise the entire time the blower is running? Sure the "cracker" asking about a belt on a direct drive blower is a bit silly, but that answer was written 4 days before the details about it being direct driver were added to the answer. Since you missed the minor detail about the start-up vs consistent noise issue, maybe you should be a bit more considerate of others before calling people names.
    – FreeMan
    Commented Apr 6, 2022 at 12:18

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