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A-1 Mechanical Blog

Why Does My Furnace Make a Banging Noise When It Shuts Off?


Furnaces, like other types of mechanical equipment, make some noise during operation, start up, and shut down. If you’re wondering why your furnace makes a banging noise when it shuts off, you’re not alone. Many homeowners throughout the Grand Rapids area have questions about this common sound produced by furnaces.

Furnace Makes Banging Noise When It Shuts Off

A banging noise is a common concern among homeowners. A-1 Mechanical explains the likely causes of this noise and what needs to be done to correct the issue.

Dirty Furnace Filter

Typically, when a heater makes a loud banging noise when it turns off, it’s the sound of metal contracting. As the furnace cycles, air is pushed through the duct system into your living areas. A dirty filter restricts airflow, causing warm air to back up in the system. This backup of heat causes the metal of your ducts and the furnace itself to expand and bow outward. Once the heating cycle stops, the sheet metal of the ductwork and the metal panels of your furnace cool and contract, producing a ‘bang’ or ‘pop’ that you hear inside your home.

To correct this cause of furnace banging noises, change the air filter. Make sure to replace filters on a regular schedule, and check them monthly over the winter season. Filters may fill up at a faster rate due to increased heating system use, requiring more frequent changes. Make sure you always use the right size filter – there should not be significant gaps between the filter and its housing. A incorrectly sized filter can also allow excess dust into your system.

Dirty Ductwork

An accumulation of dirt and debris inside your ductwork may also be to blame when your furnace makes a banging noise when it shuts off. These deposits within the ducts can hinder airflow and trap warm air inside instead of allowing it to flow into your living areas. The ducts warm up and expand, then contract as they cool once the heating cycle is finished, producing a loud banging noise. Duct cleaning removes buildup from the interior of your ductwork so air can move through the system as intended, which reduces the likelihood of a banging noise after each heating cycle.

Banging Noise When Furnace Starts

Now you know why a furnace makes a banging sound when it turns off – but what about when the system starts? It is possible for a banging sound to occur when the heater starts up. This noise is typically caused by dirty burners.

Dirt can build up on the burners over time as the system operates. Carbon also accumulates on the burners as a natural byproduct of combustion.

Dirty burners cause an issue called delayed ignition – this means dirt has prevented the burners from quickly igniting the gas. Instead, gas builds up in the combustion chamber. Once the burners are finally able to ignite, there is a larger volume of gas present, so the banging noise you hear is the sound of this gas finally igniting. If you believe your furnace suffers from dirty burners and delayed ignition, call for furnace repair right away. Ignoring this issue could lead to a damaged heat exchanger or create a possible fire hazard in your home.

Furnace Care from A-1 Mechanical

If your furnace makes a banging noise when it turns off, give A-1 Mechanical a call for fast and reliable repair service. Our technicians examine your heating system to find the source of the banging sound you hear and perform lasting repairs to eliminate the issue, restoring quiet furnace operation. Count on our team any time you experience troubles with the furnace or heating system inside your Lansing area home.

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