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Furnace Blower Motor Whistling? 4 Common Causes

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The blower motor is an essential part of your furnace; without it, the heated air in your furnace can’t travel to the rest of your home. If you hear this necessary component making a whistling noise, it’s important that you identify and fix the problem as quickly as possible. 

If your furnace blower motor is whistling, the cause could be a clogged air filter, debris around the blower fan, a loose screw on the fan mounting, a faulty capacitor, or worn fan motor bearings. The most common issue is a clogged filter, which you can easily fix by replacing the filter yourself. 

In the rest of this article, I’ll explain each potential cause of a whistling sound coming from your furnace blower motor. I’ll also explain how you can check for each problem and how to make the necessary repairs. 

Clogged Air Filter

Checking your furnace’s air filter for dirt and debris build-up is a good place to start whenever there’s an issue with the system. The filter sits between the exterior and interior of the furnace; if it gets clogged with dust, 

Many furnace owners neglect to clean or replace their filters regularly, and the resulting decreased airflow can cause a variety of issues, including damage to internal components, a decrease in your home’s air quality, and an annoying whistling noise. 

Here’s how you can identify and fix a clogged air filter:

How to Fix A Clogged Air Filter

  1. Turn off the furnace power and let the system cool down. To be safe, I recommend unplugging the furnace from the power outlet. 
  2. Open the front panel and pull out the filter.
  3. Check the side of the filter to assess whether it is permanent or disposable. 
  4. If it’s permanent, wipe the filter to remove all dust and debris. 
  5. If it’s disposable, you’ll need to buy a replacement filter. If you have the owner’s manual, it should tell you the correct size. If you don’t have the manual, you can still figure out the size by measuring the old filter’s width, length, and thickness. 
  6. Place the clean filter back into the slot and turn the furnace back on.

Pro-tip: You should clean or replace your air filter every 30-60 days. If you aren’t doing this regularly, I highly recommend making it a habit. 

Debris Around The Blower Fan 

When your furnace blower motor starts to make noises of any kind, it’s always good to examine the blower fan (sometimes called the blower “wheel”). The blower fan is responsible for pushing air in and out of the furnace, and thus plays an essential role in the heating and cooling of your house.  

The blower fan is directly attached to the motor. This means that any debris or dirt build-up can affect the furnace motor and decrease its efficiency. As a result, this can cause the motor to overheat and make a whistling noise. It can also cause other sounds such as loud humming, screeching, or banging. 

How to Remove Debris Around The Blower Fan

  1. Turn your furnace off. 
  2. Open the top panel on the front of your furnace. Depending on the make and model of your furnace, you may also need to remove a second panel to access the blower fan.
  3. Check the wiring to see if you will need to remove any lines to reach the blower fan. If you do, make sure to take a photo so that you don’t forget how to reattach them.
  4. Undo any screws or bolts holding the blower fan and motor in place, and pull the system out to where you can easily reach it. 
  5. Using a vacuum with a brush attachment, clean off any dust buildup on the fan blades. 
  6. If it still seems dirty, you can detach the motor from the fan and use water and soap to clean it. 
  7. When you’re finished, reassemble the machine and place it back into the furnace system. 

If you’d like a visual guide on how to remove the debris, I recommend watching this video:

Loose Set-Screws 

A loose screw on your fan mounting can be the cause of many strange sounds, including whistling. If this is the issue, all you’ll need to do is tighten the screw. 

How to Fix Loose Set-Screws

  1. Wait for the furnace to turn on and then listen for any strange noises coming from near the fan.
  2. Once you’ve located the approximate source of the sound, turn the furnace off and let it cool down. Before poking around in the unit, make sure it is unplugged from the power.
  3. Using a flashlight, check for loose screws
  4. Tighten anything that appears loose. 
  5. After tightening everything up, you can turn the unit back on and check if the problem is solved. 

Here’s a helpful video with more detailed tips about checking for loose hardware:

Faulty Capacitor

Along with causing your furnace to short or lose power, a bad capacitor could also be the source of strange whistling sounds. 

How to Fix a Faulty Capacitor

  1. Make sure the power supply is cut off. 
  2. Locate the capacitor and short off the two terminals so that you do not get shocked.
  3. Disconnect the wires from the capacitor.
  4. Using a digital multimeter, check the reading on the capacitor. If you don’t have a multimeter, I recommend this reliable device from Amazon.com: Extech – EX430A EX430 True RMS Autoranging Multimeter
  5. If the reading is 6% or lower, the capacitor needs to be replaced. 
  6. Once you’re done checking the device, disconnect the wires and put the leads on the capacitor terminals. The reading on the multimeter will start at 0 and go up until it’s fully charged. 

To get a better idea of how to check your capacitor for damage, this video will outline the specific steps:

Worn Fan Motor Bearings 

Another area to check if you are hearing strange whistling from your furnace motor blower is the blower bearings. The bearings are normally fitted between the armature and the housing of the motor, and are made to allow the fan to spin without friction in the housing. While bearings are made to last, they can wear down over time and begin making noises when operating. 

To get a better idea of how bearings work, check out this informative video. 

How to Fix Worn Fan Motor Bearings

  1. Once you have turned off the power and disconnected the motor blower housing from the furnace, use a flathead screwdriver to gently separate the unit into two halves.
  2. Remove the bearings from each side. Be careful not to scratch the seals.
  3. Softly wipe off any debris from the seals with a clean rag and then lightly grease them with motor oil.
  4. Put your replacement bearings into the seals and lightly grease them.
  5. Reinstall the fan housing by putting the halves back together and tightening the screws that hold them. 
  6. When the fan is back in place, twirl it back and forth with your fingers to make sure that the grease is evenly spread. 
  7. Put the motor blower back into the furnace and turn the unit on to see if the whistling is gone!

Have questions about replacing your motor bearing? Here’s another helpful video that walks you through the whole process: