Do you hear constant strange noises from your gas heater? 

The noise may be an indication of a possible issue with the fuel ignition. it could be a reminder to clean your dirty or clogged air filters or fix a loose duct or blower fan. It could be alerting you of a cracked heat exchanger, worn-out fan belt, or even a gas leak, or something more serious like a possible electrical issue.

To understand the problem, you first need to identify the type of noise.

 Is it a buzz or a hum? Is it a rattling noise? Is it like someone constantly knocking the appliance from within?- 

Any unusual noise coming from your gas furnace should be a cause of concern and checked immediately to resolve the issue at the earliest, to avoid gas furnace failure. 

Gas Heater making noise! – Image Source

Each noise alerts you of a specific problem. In this article, we delve deep into the causes for a loud buzzing or humming noise along with some troubleshooting advice. Not only this, but we also discuss other common noises from gas heaters and their possible causes. 

So read on till the end to understand the language of your gas heater! 

But first, let’s answer your query. 

Why is your gas heater buzzing or humming? How to fix them?

Most gas heaters produce a mild humming or buzzing noise while operating. This is normal. 

What’s not normal is –

When the humming noise is noticeably or endearingly loud- indicating an electrical problem in your appliance.  

Of the many possible reasons, here we have listed the 3 most common ones along with ways to fix them. 

Reason #1: Loosely mounted or a dying transformer box

Furnace transformer supplies power to the furnace by converting the main supply voltage to the one required by your gas heater. It lowers the supply voltage to the furnace voltage. 

Transformer – Image Source

This powers the furnace controls lie timers, internal circuits, temperature controls, etc. Most of the gas furnaces need a 24 Volt supply to operate these controls. 

When this transformer box is loosely mounted or is dying, the gas furnace starts humming or buzzing at a louder, noticeable decibel. 

How to fix it?

The transformer box has two wires coming out. Check it and ensure the box is securely mounted in its place. 

Reason #2: Aging Blower motor 

The Blower motor is responsible for circulating heated air from your gas furnace to various rooms through the vents. It blows the heated air until the room reaches a set temperature. 

For this, most gas furnaces in homes have direct-drive motors. The belt drive motors are more common in commercial spaces or at homes with old gas furnaces. 

Gas Heater Blower Motor

A blower motor consumes the maximum energy in a gas furnace system. So, if your energy bills are skyrocketing without any other prominent reason, the humming sound most likely indicates that the motor blower is wearing down and is near its fad end. 

How to fix it?

To confirm the noise attributes to an aging blower motor it is best to consult an HVAC contractor. Once confirmed, it is most likely that you may have to replace the blower motor or clean up the motor to free it from the debris if any. 

Reason #3: Blowing motor capacitor failure

The most common blower motor capacitor in modern gas furnaces is the permanent split capacitor, where the capacitor relies on the run capacitor to start. However, if you have an old system, there will be two capacitors-start and run capacitors. 

A healthy blower motor capacitor will start the blower motor with a slight humming sound. If you notice that the motor does not start, yet has an unusual humming sound, it may indicate a faulty capacitor.

How to fix it?

The humming sound in this case is indicative of a normal blower motor. Therefore, only a capacitor replacement might be required to resolve the issue and get the blower motor back in action. 

Other strange noises to look out for

A humming or buzzing sound is associated with an electric problem of the gas furnace, some other noises indicate a faulty gas furnace. You must know the possible reasons behind each of these sounds to troubleshoot the problem accordingly. 

#1. Banging Sound

Do you hear loud bangs from inside the furnace? There could be possibly 2 reasons for this.

Reason #1: Your gas furnace is trying to tell you about a possible issue with its ignition.

Normally, when the gas valve opens at the start of the furnace cycle, the ignition system ignites the gas right away. 

However, with a faulty ignition system, some residue gas can pile up in the combustion chamber. This gas build-up causes banging noise. 

Reason #2 Contraction and expansion of metal ducts 

Since most ducts are thin metal that contract and expand when the air temperature heats or cools off completely. It could also be a reason why you hear banging sounds while your gas furnace is on.   

Try replacing the rectangular ducts with circular ones, or use a thicker metal for the ducts to reduce the decibel of the bangs. 

#2. Whistling Sounds

Whistling indicates an issue with the airflow of your furnace, such as a blocked air filter, blocked return, objects stuck in the ducts, closed vents, or dampers. 

A simple clean-up of the ducts or filter or return will most likely solve the issue. In the case of an aged air filter, you may also need air filter replacement to resolve the whistling sound. 

Another reason could be that your furnace is bigger than the ductwork or that the blowers or burners need a quick check to identify possible issues.

#3. Clunking/Knocking Sounds

Clunking or knocking noise indicates a faulty gas furnace. 

It could be a misaligned fan with blades that hit the furnace walls. When they hit the surfaces, you hear a loud knocking or clunking noises inside the gas heater. 

It could also indicate that a cracked or split fan belt is hitting other surfaces. 

#4. Screeching Sounds

Screeching or scraping sounds are similar to the noise when you scratch a metal on another metal surface. The reason you hear these from your gas furnace can be many. 

It could be the loose blower fan, whose blades are dragging across the furnace casing. It could also indicate that some other metallic part of the gas furnace has become loose and needs proper fixing. 

#5. Rattling Sounds

Rattling sounds from your gas furnace usually do not indicate anything serious with your gas furnace. It could mean some parts like duct joints are losing heat, or your vent opening is bigger than ducts. In the latter case, the duct moves to and fro, creating a rattling sound every time air passes through the ducts. 


Strange noises from your gas furnaces are annoying but not always a cause of concern. This article sums up some of the common noises and their possible causes. To fix the issue, it is always best to contact a local HVAC technician to keep your gas furnace healthy and running. 


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