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Furnace Making Buzzing Noise? 4 Common Causes (+ Fixes)

If your furnace is making a buzzing noise, you shouldn’t ignore it! This type of sound indicates a potential electrical issue in the furnace. Not attending to the underlying cause can result in significant damages.

Your furnace is making a buzzing noise because of problems with wiring, the capacitor, blower motor, or transformer. You can stop the buzzing noise by diagnosing these electrical components and replacing or fixing them. Alternatively, a certified HVAC electrician can repair the furnace for you.

In this article, I’ll discuss how to identify the source of the buzzing noise, why it happens, and what you can do about it. 

Faulty Wiring

A buzzing sound generally means something is wrong with the flow of electricity inside the furnace. In many cases, you’ll find that the problem lies with issues related to the electrical wiring.

There are many electrical wires running through your furnace. The power source connects to the furnace’s interior, where the control board, blower assembly, thermostat, and several other parts get supplied with sufficient power. 

If there are loose wires in the system, you’ll hear a consistent buzzing sound while the furnace is operating. However, there can be another reason behind the problem. Damage to the copper wires’ insulation can also be why buzzing sounds develop. 

Two bare wires touching against one another is another potential cause. In addition to the annoying buzzing sound, it can also be a major electrical or fire hazard in your home. 

How To Fix

You need to access the interior of the furnace’s main compartment to inspect the wiring. Since there are a lot of wires, the process can take some time:

  1. Turn the furnace off completely. Unplug it if possible. You’ll be handling electrical wires, so you want to ensure no power is running through them. 
  2. Open the door to the furnace compartment and take a look inside. Start at one point and slowly move over all wires. See if you can identify a loose wire. Perhaps a wire hasn’t fallen out but isn’t fastened to the appropriate plug properly. 
  3. Take a look at the insulation surrounding the electrical wires in your furnace. See if you can find damaged insulation. This could be the source of the buzzing sound too. 

Problems With the Capacitor

The capacitor is another important electrical component of your furnace. The capacitor sits close to the motor and is responsible for starting it when you turn the furnace on. This device is directly connected to a power source within the furnace and can get faulty over time. 

The capacitor can develop a few different issues. For example, a power surge could damage the interior components. Also, an imbalanced motor could push against the capacitor, shifting it out of position. 

Problems with the capacitor can sometimes lead to a buzzing noise in the furnace, depending on the issue at hand. When the buzzing comes from the capacitor, you’ll hear it during the furnace’s start-up process. Once the furnace has started, the noise should go away. 

How To Fix

If the furnace making buzzing noise only occurs during the start-up, inspect the capacitor. You can look for visual signs of damage and check for loose wires. These are two steps you can do yourself. If you don’t find any valuable data from these two checks, you may need a professional to test the capacitor if you don’t know how to use a multimeter.

If you find loose wires on the capacitor, fasten them. If you notice physical damage, you may need to replace the whole component. Also, check if it’s mounted correctly. If it isn’t, secure it in the correct location before closing the furnace compartment door. 

Faulty Blower Motor

The blower motor connects to the capacitor and blower fan. Problems with the blower motor or its connections can also cause a buzzing sound in the furnace. 

Note that a faulty blower motor will produce a more persistent buzzing sound than a bad capacitor or faulty wiring.

How To Fix

Inspecting the blower motor will help you determine if wires are connected correctly and if there’s physical damage. In most cases, you need to test the blower motor thoroughly. Try to connect it to an external power source and see if it makes a buzzing noise. 

If the blower motor itself is causing the buzzing noise, you’ll have to buy a replacement.

The video below details the procedure for replacing the blower motor in a furnace:

Problems With the Transformer

The transformer plays a large role in assuring the furnace can start when you turn it on. The transformer is situated inside the system. It regulates the voltage supplied to the furnace. A low voltage will cause problems with the furnace’s functionality, usually leading to insufficient heating and air distribution. 

When the voltage provided through the transformer’s regulation is too high, there will be electrical shortages and power surges in the device. This can cause damage to internal components, such as the control board. It can also be the source behind that buzzing sound you hear when the furnace is powered on. In some cases, the transformer may continue to make a buzzing sound even when the furnace isn’t even on. 

How To Fix

You first need to determine why the transformer is causing a buzzing sound. It’s typically related to one of the following problems:

  • The transformer is allowing too much voltage to pass into the furnace. This causes electrical damage to the components in your HVAC system, leading to the annoying buzzing sound. 
  • Wires in the transformer are faulty or not connected properly. There may also be open wires in the transformer — they can cause electrical sparks, but they’re not big enough to cause a fire. They can still make a buzzing sound, however. 
  • The box on the transformer isn’t fastened tightly with screws. This can cause a buzzing or humming sound. Securing the box properly will stop the noise. 

If you find that the transformer is damaged, you should replace it. You can watch the video below for instructions on the replacement procedure:

Summary

While some noises are considered normal as the furnace starts, you shouldn’t ignore a buzzing sound. It may be related to several electrical problems with the furnace, including faulty wiring and issues with certain electrical components.

Author

  • Chris Hewitt

    Chris is a Texas-based freelance writer who loves the outdoors and working in his garage. When he's not enjoying the Texas sun, he can be found tinkering with all sorts of things in his workshop.

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