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Why Is My Furnace Humming? Top 6 Reasons (+ Easy Fixes)

A humming furnace is both annoying and concerning. Is it a normal part of furnace operation, or is something wrong?

A humming furnace is a sign that parts of the furnace are not working correctly. It could be loose furnace parts, a faulty blower motor, a damaged plenum, a faulty transformer, or dirty gas burners. When your furnace is off, an incorrectly adjusted blower pilot light can also cause your furnace to hum.

While most furnaces will emit some soft sound when running, a loud humming or buzzing sound indicates trouble. In this article, I’ll explain the possible causes and walk you through how to fix each of them. I’ll also let you in on the easiest way to fix your humming furnace. (Check the bottom of the article.)

Let’s get started!

Faulty Blower Motor 

The furnace blower motor is what sends warm air from the furnace into your home through the duct system and the vents. There are two issues that can cause the motor to emit a humming sound: poor lubrication and a motor that is overly worn close to failing.

Poor Lubrication

A furnace motor moves a lot to turn the fan and move air out from the furnace to your home. That means it must remain well lubricated to preempt damage and consequent repair or replacement bills. 

An Overly Worn Motor

An imminent blower motor failure is usually announced by unusually slower speed. Whereas your furnace blower will normally slow down to save power once the set temperature has been reached, unusually slower speeds often indicate wear-related faults in the blower or capacitor and are often the cause of humming.

An overworked motor will also give a buzzing noise and is often caused by dirt and dust in the filter, making the motor work extra hard to send air out. 

What to Do About a Faulty Furnace Blower Motor

If the problem with the motor is poor lubrication, you can remove the motor and oil it. This should be done annually, and it is important that you do it correctly. The following video walks you through the motor oiling process. Be warned that it’s complicated and messy, and you may be better off hiring a furnace repair specialist to do it for you.

If your blower motor is worn, there isn’t much you can do about that – replacing it will usually be the best move. To prevent motor failure and furnace humming due to dirt buildup in the future, you should clean the furnace filter regularly to rid it of debris.

A Damaged Capacitor

Capacitors are the two pieces in the motor of the furnace that provide needed electricity to the furnace parts. A start capacitor helps ignite the furnace, while a run capacitor helps provide a steady power supply to the fan motors.

Damaged capacitors won’t run smoothly, and will affect all other parts of the furnace. Damaged capacitors usually cause the motor to stop turning while producing a humming noise. Sometimes, broken capacitors may have their root cause in blocked filters.

What to Do About Damaged Capacitors

If you have kept your filter cleaning schedule and your capacitors are not working, you most likely need to replace them. Call an HVAC professional and have the capacitors checked with a multimeter to establish their capacitance (electrical capacity) and figure out if they’ll need to be replaced.

After replacing your capacitors, a professional will also determine if the furnace overheated as a result of the malfunctioning capacitors and if the safety buttons need to be reset.

Loose Furnace Parts

Furnace parts are always moving when it is on. And if your furnace is old or poorly maintained, nuts, belts, and bolts can easily become loose. This could be extremely dangerous as furnace parts can fall apart with time. But humming is one of the early signs of loose furnace parts.

What to Do About Loose Furnace Parts

If you’re particularly handy, you can open your furnace and test parts by manually moving them to see if any are loose enough to make a humming noise.

Ensure your furnace is not powered on before opening your furnace up, You should also use a wooden tool to move parts rather than your fingers, as some parts such as capacitors store electricity even when the furnace is not powered.

If you don’t trust your furnace maintenance/repair expertise and prefer to be sure rather than sorry, contact a licensed HVAC technician and have them make the repairs.

Damaged Plenum and Ductwork

To transport warm air from the furnace into your house, your furnace’s heat exchanger directs it to the supply plenum and through the ducts into your house. These two parts of the system are made out of thin sheet metal, and if the passages have loose or worn out parts, they can vibrate and hum when the furnace is on.

What to Do About Damaged Plenum and Ductwork

To fix this, you’ll need to seal loose sections of the duct and plenum and tighten loose seams or screws to seal off any air leaks and humming. This is pretty tricky, so I suggest letting a professional handle it.

A Faulty Transformer

An electric transformer supplies power to the furnace and ensures that the power level is controlled to fit the power needs of each furnace function. So, it will lower the power supply when the furnace is slowed down and provide higher voltage when the furnace has just ignited.

Even though it may not seem likely, a faulty transformer can cause your furnace to hum by simply having power passing through it.

What to Do About a Faulty Transformer

Electrical faults can be tricky and should be handled by a professional. A humming transformer is headed for damage sooner rather than later, and the technician will probably recommend that you replace it.

Dirty Gas Burners

Dirty or rusty gas burners compromise gas supply, furnace ignition, and overall function. They can also cause a humming or rumbling sound.

What to Do About Dirty Gas Burners

You can troubleshoot your dirty gas burners problem by simply opening the furnace and cleaning the gas burners. 

Pass a soft-bristled brush over the surface of the burners to remove rust and dust. You can use a vacuum cleaner wand to suck up excess debris as you remove the dust with the brush. You should also take care of the gas jets while you’re at it by simply passing a thin wire through the jet hole.

Sticking to annual maintenance schedules will save your gas burners from getting to this point. A professional technician will also be able to tell you if your burners need to be replaced.

Incorrectly Adjusted Blower Pilot Light

The blower pilot light is a small flame that stays on in some gas furnaces to ignite the burner when the gas is turned on. If this light is not adjusted correctly, it can cause your furnace to hum while it is turned off.

What to Do About a Wrongly Adjusted Blower Pilot Light

Readjusting your blower light to the appropriate level will fix the humming. This guide from Hunker.com provides an easy step-by-step walkthrough.

The Easiest Fix for a Humming Furnace

If you don’t have the time or expertise to troubleshoot and fix your humming furnace, the smart decision — as you know — is to hire a furnace repair expert to fix it for you.

The problem is that finding a trustworthy and affordable repair service — and actually booking an appointment with them — can feel like pulling teeth.

Some services never call you back. Others charge criminally high rates. The best options are often booked out for months… and the worst don’t even fix your oven. (But they charge you for it anyway.)

To save you from that teeth-grinding frustration and bring you fast and affordable repairs from top-rated pros, I’ve partnered with a company called Networx. They work with thousands of contractors across the United States, and they make it easy for you to get free furnace repair quotes from the best repair services near you.

Here’s how it works in 7 easy steps:

  1. Go to the form below.
  2. Select your type of furnace in the dropdown menu. Options include Electric Furnace, Gas Furnace, Oil Furnace, and Propane Furnace.
  3. Add some basic contact information and a brief description of your problem. (Your information will only be used to provide you with furnace repair quotes.)
  4. Click the “Get Free Quotes” button when you’re done.
  5. Our repair service partner will contact multiple vetted furnace repair experts near you. They’ll explain your problem and ask each service to contact you with a free quote.
  6. You’ll receive an email or phone call with repair quotes from each service. You can choose the most affordable option and schedule your repair directly with them.
  7. They’ll come to your house and fix your oven. Problem solved!

Using this form to find the best repair rates is 100% risk-free. There is zero obligation to hire any of the vetted contractors who contact you.

Fill out the form now to get free quotes from trusted furnace repair services in your area.

Author

  • Steve Rajeckas

    Steve Rajeckas is an HVAC hobbyist with an avid interest in learning innovative ways to keep rooms, buildings, and everything else at the optimal temperature. When he's not working on new posts for Temperature Master, he can be found reading books or exploring the outdoors.

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