No one wants to hear banging from a furnace during Decatur, AL’s cooler months. But on occasion, it can happen to any furnace—and you’ll want to find the cause quickly to settle your nerves and to get the problem fixed.

There are several reasons a furnace could be making a banging sound, but the good news is that some of the reasons are simple, and the problem may be fixed quickly by a trained HVAC professional.

These noises might not always be a “bang.” You may also hear:

  • Knocking sounds
  • Popping sounds
  • Thudding sounds
  • Repetitive sounds or sounds that only occur during a certain phase of a furnace heating cycle.

Reason #1: Ignition is happening late. If you have a gas furnace, when your furnace turns on, gas will build up until everything fires up, creating the heat that circulates through your home. But if the ignition gets delayed for any reason, more gas could enter your system than usual. This can lead to a mini explosion in your furnace, creating that “boom” sound. You’ll hear this sound at the beginning of your heating cycle.

Late ignition can be caused by a few things, namely dirty burners, a defective ignitor, or a pilot light that’s too weak. You’ll want to get the issue fixed by a professional, as such an ignition can damage other parts of your furnace over time, such as the heat exchanger.

You may only need to have your burners cleaned if you’re getting this symptom, or you may only need a fairly inexpensive replacement of a part. Leaving such a problem for too long may damage your heat exchanger, which will most likely mean you’ll need a new furnace.

Reason #2: Your ductwork is doing what metal does when heated and cooled. If you notice some pops, thuds, or knocks during other parts of the heating cycle, your ductwork may be to blame. These noises will typically occur after the ductwork has been heating up for some time, or while it’s cooling. You may even notice these noises after your furnace turns off!

This issue happens primarily with sheet metal ducts, as this material will expand and contract with temperature changes. To check if this is the case, stand near where you’ve heard the sound as your furnace runs. This will help you narrow down the issue. Better yet, stand near some exposed ducts in your basement or attic if you have them.

Noisy ductwork is not an emergency, and you may be able to live with this minor issue. but if it’s disruptive, a professional will help you replace the problem section. And of course, it’s always a good idea to call in a pro if you have doubts as to what’s happening.

Reason #3: The banging is actually the rattling of loose parts. If you’re hearing the banging sound while your furnace is on, and the sound is more chaotic, then you may have a loose bolt, fan blade, or other part in your furnace. This is an issue that can lead to more damage to your system, and more expensive repairs, if you don’t get it addressed by a professional. After all, metal against metal will make a banging noise.

Get to the bottom of that noise today. We’ll help you discover the source of your furnace’s odd sounds at Southeastern Mechanical Services. If you’re in the Decatur, AL area, contact us today.