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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 Dec 25 '11 at 13:26
    
What type of fan/motor combination do you have: direct drive or belt? –  RSMoser Dec 29 '11 at 21:13
    
Looking for some kind of response from Paul here to determine if any answers are bounty-worthy. –  The Evil Greebo Jan 3 '12 at 14:43
    
Paul, I know you were here 3 hours after I posted my last comment. You should pay more attention to your questions if you want people to invest time in helping you. –  The Evil Greebo Jan 4 '12 at 13:07

3 Answers 3

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 Dec 29 '11 at 21:14

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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