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

Banging noises coming from your furnace is something that shouldn’t go unaddressed. The problem may even be related to incompatible components within the HVAC system that could cause severe damage if ignored. Thankfully, finding and fixing the source of the noise is relatively simple. 

Your furnace is making a banging noise because of a delayed ignition, clogged air filter, or problems with the ductwork. Fix the problem by inspecting and resolving the problem with the ignition, replacing the air filter, and cleaning the ductwork. Also, ensure the ducts are the right size.

This article explores the various reasons your furnace is making a banging noise. I’ll also share with you how to fix each potential problem. 

Delayed Ignition

A good starting point is to determine where and when exactly the banging noise is coming from. This will help you pinpoint the root of the problem.

A common reason behind banging noises is the ignition. In particular, there may be a delay in the ignition process. The banging noise will be coming directly from the furnace unit in this scenario. And it’ll happen during the ignition process, of course. 

Gas is released into the furnace to provide fuel for the ignition process. Sometimes, however, the ignition process is delayed. When this happens, gas starts accumulating in the combustion chamber. The large amounts of gas create a loud bang upon ignition. 

This problem is serious, as the “mini” explosion inside the furnace can damage the interior components. 

How To Fix

There are a few reasons why gas may build up in your furnace. To fix this problem, you need to understand why it happens: 

  • Low gas pressure. When gas pressure is too low, less gas gets pushed to the burners. As gas continues flowing to the burners, some of it can escape and accumulate around the burners too. 
  • Dirty pilot light. Sometimes, the pilot light is too weak as well. This makes ignition harder, leading to an accumulation of gas before it can ignite. 
  • Dirty burners. If the burners are dirty or not in place, gas builds up before ignition. 

Here’s a video that shows how to properly clean all components in your furnace:

Clogged Air Filter

A dirty air filter is a common issue people run into with their furnaces. This happens over time, as particles and debris, along with gas residue, start to build on the filter. 

The filter is responsible for filtering the air pushed into the ductwork. The air travels through the ductwork to get to different rooms in your house.

When the air filter is dirty, you get less hot air. This causes negative pressure, leading to the duct being pushed in. Pressure in the ducts must be consistent.  When there’s a pressure drop, this inward pushing of the ducts can cause a banging noise. 

How To Fix

If the air filter is causing a banging noise in the furnace, the sound won’t come from the main unit. Instead, it’ll originate from the ducts, which means you’ll hear the sound at a distance when standing next to the furnace. 

Cleaning or replacing the air filter is the right solution. The air filter is located in the main furnace compartment and is easily removable. The filter is fastened to the furnace, ensuring it remains in place as air is pushed through the filter. 

Here’s how to clean or replace the filter:

  1. Turn off the furnace.
  2. Open the door to the main compartment. 
  3. Remove the filter using the appropriate tools. 
  4. Replace or thoroughly clean the filter. Be gentle to avoid cracking or damaging the filter. 
  5. Once cleaned, put the filter back into the furnace and fasten it.

Furnace filters need replacing every 30–90 days (depending on the type) to ensure proper functioning.

If you’re struggling to clean the air filter, watch the video below:

Wrong Size Ductwork

Sometimes, incompatible parts are behind your furnace’s banging noise. You should consider your ductwork’s size if the sound is coming from the vents. Wrong-sized duct lines lead to several problems. 

When the ducts are too small to handle the pressure, you may hear a banging noise. This happens when the air pushed into the ducts pushes the panels out. Over time, the ducts will get damaged if you don’t address the problem now. 

How To Fix

Start by evaluating the size of your furnace. Take note of the air pressure the furnace applies to the ducts. If the pressure is too high for the ducts, consider one of these two options:

  • Replace the furnace with a smaller model. This will restrict the airflow to your home. 
  • Replace the ducts with bigger ones. This provides better compatibility with the existing furnace model and allows maximum airflow.

This video explains how ductwork is installed in an HVAC system:

Dirty Ductwork

When there’s an excessive collection of dirt and debris in the ductwork, you’ll face many problems, including a banging noise.

Most importantly, the particles end up in your home. This means your family will experience respiratory problems and allergies if you don’t clean the ductwork.

How To Fix

Thoroughly cleaning the ductwork is an easy solution. You’ll need to remove panels from the ductwork one by one and then clean the duct lines. 

You can use a brush to get most of the debris out of the ductwork. If there’s dust and dirt in smaller corners of the ductwork, use a toothbrush. When you’re done cleaning the ducts, make sure to fasten all panels properly — you don’t want loose panels as this would result in a flapping sound while the furnace is running. 

Summary

Delayed ignition is a common reason for banging noises coming from the furnace, but the sound can also occur due to a dirty air filter, debris in the ductwork, or an undersized duct line. You don’t want to ignore a banging noise as the problem can progress. 

Author

  • Jake Alexander

    Jake is a freelance writer from Pennsylvania who enjoys writing about science and sports. When he's not writing for Temperature Master, he can be found watching the NFL or playing basketball with his friends.

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