furnace makes humming noise when off

Reasons Why A Furnace Makes Humming Noise When Off

Do you ever find yourself lying in bed, and the house is quiet and dark? Then suddenly, you hear a faint humming coming from the depths of your furnace. It might sound uneasy but don’t worry. It’s probably just your furnace. But why does it make that noise when it isn’t even running? Chances are, there could be a variety of underlying causes to this phenomenon. From loose wiring to aging parts within the heat exchanger, understanding why your furnace makes a humming noise when off can help prevent more severe problems from arising down the road.

So let’s take an in-depth look at why the mysterious heating system hums and whines so you can get back to counting sheep without any worries!

Loose Parts

Loose parts inside the system can often cause the hum that may be heard when your furnace is off. Loose parts such as motors, fan blades, or belts can vibrate and create a low humming sound that is hard to ignore. If you have ever heard a high-pitched noise from your furnace, it’s likely due to some loose part.

For example, if a fan blower motor mount becomes worn out or begins to separate from the frame, it can cause an irritating vibration that resonates throughout your house. The same type of issue can occur with belts too. If they become loose or stretch out over time, they will create extra tension on the other system components and cause them to vibrate, leading to a humming sound when the furnace is off.

Blower Motor Issues

Another common reason your furnace may be making a humming noise when it is off is due to issues with the blower motor. If the motor mounting brackets are worn or corroded, they can cause vibrations in the system, which lead to a humming sound. Additionally, if the bearings in the blower motor become worn down, they may not be able to keep up with the demands of your system and will create extra vibration.

It’s important to remember that any extra tension put on the blower motor, such as a clogged air filter, will also contribute towards increased vibrations and humming noises coming from your furnace when it’s off. It’s best practice to check your air filter every month and replace it if necessary.

In addition, having an HVAC technician inspect your blower motor once per year is recommended to ensure everything is running smoothly and not causing any additional problems.

Failing Ignitor

A third potential cause of humming noises from your furnace when it is off could be a faulty or failing ignitor. The ignitor is the component responsible for lighting the gas burner inside your furnace, and if it fails, it can create a humming sound. It can occur due to wear and tear over time or due to dirt or debris clogging up the part and preventing it from functioning properly.

To check the condition of your ignitor, you’ll need to shut off power to the system and disconnect any electrical connections for safety precautions. Once this has been done, you’ll need to remove the access panel on the side of your furnace so that you can inspect the ignitor for any dirt or buildup.

It’s also important to note that if you’re hearing a loud banging noise from your furnace instead of a hum when it is turned off, this can also indicate an issue with the ignitor.

Clogged Air Filter

A clogged air filter is one of the most common causes of a low hum or buzzing sound coming from your furnace when it is off. The air filter, located in the return duct of your system, plays an important role in preventing dust and debris from entering the blower motor and damaging its operation.

However, the air filter can become clogged with dirt and grime over time, leading to restricted airflow. This lack of proper airflow can cause extra stress on the blower motor, resulting in a low humming noise from the furnace when it is off.

The best way to prevent this issue is to check your air filter regularly, at least once monthly, and replace it if necessary. It’s also important to use the right size filter for your system. An ill-fitting air filter can create additional problems, such as increased energy bills or even damage to components within your furnace.

Thermostat Problems

Although it may not be the most common cause, thermostat problems can also contribute to a humming noise from your furnace when it is off. If the thermostat is not calibrated correctly or has an outdated battery, then this can lead to a low hum emitted as the furnace attempts to work. Additionally, if you have recently had any electrical work done around your home, this could also have caused an issue with your thermostat’s wiring and led to humming.

To check whether or not your thermostat is causing the humming sound, you’ll need to look at its settings first to see if there are any faults within the thermostat, such as an old battery or incorrect calibration. You must address this before pinpointing any other causes of your furnace’s noise. If possible, try replacing the thermostat altogether, as faulty circuitry in older models may only become more problematic over time.


It’s important to remember that regular maintenance of your furnace and its components are paramount for avoiding any potential issues. It includes checking the air filter, ignitor, and thermostat every month and replacing worn-out components to prevent future problems.

Additionally, if you experience any low humming noise from your furnace when it has been turned off, you may need to investigate further into the cause of this sound. Checking the air filter, electrical components such as ignitors, and even the thermostat can help you identify what is causing the noise and address it. It’s, therefore, essential to carry out routine checks to ensure that your furnace is running effectively and efficiently all year round.