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Furnace Making Rubbing Noise? 3 Common Causes (+ Fixes)

A furnace making a rubbing sound can be pretty alarming. Whether soft or loud, any weird noise from your heating equipment is enough to give you the heebie-jeebies, and you want to find out what it is as it can cause the furnace to stop working when it’s freezing outside. 

Your furnace is making a rubbing noise because of a loose or broken blower wheel or worn-out blower motor bearings. You can fix the problem by inspecting the blower wheel and fixing any issue you encounter. Alternatively, replace the entire blower assembly to stop the rubbing noise.

In this post, I’ll discuss in detail why your furnace is making a rubbing noise and how to fix it. I’ll also go over a few helpful tips to prevent furnace noises in the future.

Loose Blower Wheel

The blower wheel is part of the blower motor and is responsible for moving hot air into the ductwork. If it disconnects from the motor shaft, you’ll hear a loud rubbing noise coming from the furnace as the wheel rubs against other internal components.

This means the blower wheel isn’t working correctly. As a result, the heat exchanger will start to run hotter, putting the furnace at risk of premature breakdown. If the problem isn’t resolved fast, your system will automatically shut down and won’t come on until you have fixed the offending part. 

That’s all well and good, but what makes a blower wheel detach from the motor shaft?

The most common cause is dirt buildup due to poor furnace maintenance. If you haven’t been changing your air filters regularly, the filth trapped on the filter can make its way to the blower wheel, making it difficult for the wheel to push hot air out of the furnace. 

The blower wheel will be forced to work harder to do its job. The excess strain is why the wheel detaches from the blower shaft, and your furnace starts making a rubbing noise.

How To Fix

To fix a loose blower wheel, follow these steps:

  1. Turn off the power to your furnace.
  2. Open the blower chamber and locate the blower wheel.
  3. Tighten the screw attaching it to the blower shaft.
  4. Close the chamber.
  5. Turn the furnace power back on. 

Wait to see if the problem has been solved. Proceed to the next section if you can still hear rubbing noises. 

Broken Blower Wheel

Open the blower chamber again and detach the blower wheel from the shaft. Inspect the wheel thoroughly for damages. See if there are any cracks, and try to spin the motor with your hand. If it’s broken, it must be replaced. 

How To Fix

Involving an experienced HVAC technician at this point is a good idea, as you want to be sure you’re installing the right blower wheel for your furnace. An expert can also examine the system to determine what caused damage to the previous wheel and suggest ways to keep the new one in good shape. 

Worn-Out Blower Motor Bearings

Some older furnaces have bearings on the blower shaft and motor that require annual lubrication. These bearings allow the armature to spin freely without friction

If the motor develops problems that cause it to overheat, the oil responsible for lubricating the bearings will break down, causing them to rub against each other. Inadequate airflow is one reason the blower motor overheats, which can be prevented by changing your air filter regularly. 

How To Fix

To get your bearings working optimally again, apply non-detergent motor oil to each port, making sure not to over-lubricate. If there are oil ports in the blower shaft, lubricate the shaft and follow the same procedure. 

But some blowers have grease cups instead of oil cups. If this is what you have, just locate the cups and fill them with bearing lube. You can get the lubricant at any automotive or hardware store near you. 

If your motor bearings are worn out, you need to replace them. Lightly lubricate the bearings with oil to ready them up. 

Note: Only use 10-weighted non-detergent motor oil to lubricate your bearings, not all-purpose oil. Also, don’t apply more oil than necessary; 3 or 4 drops should be enough to get the bearings to work.

How To Prevent Noises Coming From the Furnace

You can prevent all types of noises coming from your furnace by ensuring the blower is receiving sufficient air. There are a few ways to achieve this:

Ensure You Have a Clean Air Filter

I can’t emphasize enough the importance of having a clean air filter in your furnace. Dirty filters cause most furnace issues, including the malfunctioning of the blower, blower motor, and bearings resulting from restricted airflow. 

If you don’t want to deal with a furnace making a rubbing noise, replace your air filters regularly. Ideally, you should change your furnace filters every 30 days.

Note that different filters come with varying requirements of maintenance based on their lifespan and effectiveness. Read your equipment manual to find out how often you should replace your filters as well as the best filter to use.

Nevertheless, changing a filter takes only a few minutes. Just remove the old one and slide the new one in. Arrows on the filter will show you how to orient it based on airflow direction.

Keep the Vents Open

Don’t close vents in some rooms thinking the furnace will redirect the hot air to other rooms to warm them faster. This only strains the blower motor, causing it to overheat the system and the motor bearings to lose their lubrication. 

And not just that. Closing vents restricts airflow, straining the blower. As I stated earlier, this will loosen the blower wheel from the motor shaft or even break it.  

Seal Leaky Ducts

The hot air produced by the furnace travels to your indoor spaces through a network of ducts. If there are holes and cracks in the ductwork, air will escape before reaching your home. And with just a small amount of air entering the room, it means that there will also be very little air going back into the system. 

The result: The blower wheel will be forced to work extra hard to maintain your desired temperature. This additional strain will break down the lube on motor bearings, detach the blower wheel from the motor, or even destroy the wheel. 

If your furnace is making rubbing noise and some spots in your home are hotter than others, check for leaky ducts. Have these sealed before repairing the blower wheel. After this, make sure to inspect your ductwork frequently for leaks. 

Schedule a Professional Furnace Inspection

Have an HVAC expert inspect your furnace once in a while to make sure things are running as they should. A professional will keep the system tuned up and help you resolve airflow problems before they get out of hand. 

Conclusion

Problems with the blower compartment are the primary reason why a furnace makes a rubbing noise. In most cases, it’ll be because:

  • The blower wheel has separated from the motor shaft.
  • The blower wheel is broken.
  • The motor bearings have lost their lubrication.

While you can tighten the blower wheel or re-lubricate the motor bearings yourself, complex tasks like replacing the wheel should be left to an expert.

If you’re uncomfortable making the repairs yourself, or your furnace still isn’t working after attempting these fixes, I recommend calling a professional to fix it for you.

Author

  • Alanna Greene

    Alanna is an avid traveler who lives in Michigan. In addition to writing for Temperature Master, he also sells crafts on Etsy and takes long walks through the forests near her home.

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