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Why Is Furnace So Loud?

Modern furnaces are not supposed to have many issues that older models had, like too much noise. A lot of attention has gone into making them as quiet and efficient as possible, which is why it is normal to be alarmed when they become loud. If you have ever found yourself wondering why is furnace so loud, you are not the only one. However, understanding the different types and causes of furnaces, including mid-efficiency furnaces, noise can help put your mind at ease when such a problem occurs.

Common types of furnace problems you are likely to encounter

‘Why does my furnace sound so loud?’ is a common question among homeowners, and understanding the furnace problems could give you an answer.

Type of problem: Whistling

Cause: Clogged or dirty furnace filter

Furnace filters are susceptible to dirt and dust accumulation, which can quickly clog them within a short time. When that happens, it restricts airflow in and out of the furnace, which causes the screeching whistling sound that you may hear when the furnace is in use or is turned on. Such a problem is usually easy to fix because filters are cheap and do not necessarily require professional assistance to change.

Tip: The first step is to check the cleanliness of the filter and replace it with a disposable one. If a disposable one is not available immediately, you can operate the furnace without a filter for a short period as you look for one or clean the clogged one if it is reusable.

Operating the furnace with a dirty filter can cause further problems, such as damage to the fan motor and heat exchanger. That is why it is better to check the filter every month and change or clean it every three months. Getting an extra disposable one is also important.

Problem type: Screeching

Cause: Damaged or poorly functioning blower motor and wheel

The blower wheel in a furnace is normally responsible for optimal air circulation, which means that the furnace stops working efficiently if it becomes loose.  The screeching sound is also similar to the scraping sound, and it signals the blower wheel bumping against the shell of the blower.

The furnace noise is also caused by a blower motor that needs to be lubricated. Failure to do so could result in warm air not pushing through the ducts as efficiently as it should, resulting in a furnace that consumes too much energy without making the room warm.

Tip: Turning off the furnace and calling in professionals is the best way to deal with the loud furnace motor. Lubricating the blower motor and cleaning the wheel at least once a year also keeps such problems at bay.

Type of problem: Rattling

Cause: Cracking in the heat exchanger

A furnace making a rattling noise could have a damaged heat exchanger, restricting  proper airflow within the appliance. It is usually prevalent in furnaces with filters that have gone for long without being cleaned or changed. The restricted airflow causes heat to build up, eventually taking a toll on the heat exchanger and cracking it. A cracked heat exchanger is very dangerous because it leaks carbon monoxide. It can set off an alarm if you have one.

Another common furnace problem that can cause a rattling sound is a loose screw.

Tip: Turning off the furnace and searching for loose screws is the first step. If they are any loose screws, use a screwdriver to tighten them while being careful not to damage any other part. It also helps to check the state of the heat exchanger, but this should be done by a professional. Have an emergency contact for an experienced HVAC contractor for such situations, and make sure there is a functional carbon monoxide detector. Regular maintenance of the furnace is also crucial.

Problem: Banging

Cause: Issues with the ductwork

A bang that occurs a few seconds after the furnace is turned on can be a sign that the burners are dirty, which is causing the delayed ignition. The gas that builds up during ignition can cause a banging sound when it finally lights up.

Ductwork flexing when the pressure between the supply and return duct differ is another cause for furnace making noise. The problem is referred to as oil canning, and it happens when there is a specific area that has degenerated in the duct and requires reinforcement. Oil-canning sound is usually consistent, which is unlike the regular pops in older furnaces.

Tip: A banging sound, which is a result of a duct problem, usually requires professional attention to fix. However, you can try to follow the sound to pinpoint it to a specific area to make the professional’s work easier. The professionals can also clean the burners thoroughly; this should be done at least once every year. Regular inspections are also essential in preventing such problems.

Problem: Furnace blowing cold air

Cause: Heating system issues

In most cases, the sound of cold air blowing happens when the thermostat is not set properly. For instance, if it is on “ON” instead of “AUTO”, it will blow air even if there is no heat. The “AUTO” setting ensures the furnace only releases air when it has been heated.

Tip: Always check the thermostat and clean the filters to ensure the heating system works perfectly every time. If unsure, call Air Makers for help.

Other causes for furnace noise

Persistent clicking sounds: Furnaces produce rapid clicking sounds when turned on and off, but it typically subsides quickly. If it goes on for over one minute, it could be a sign that the furnace has an electrical problem.

Fluttering: This sound is typically like the sound of cardboard stuck on a bicycle tire, and it usually indicates that there is debris stuck on the furnace fan.

Squealing: Squealing is typically produced when there is one component of the furnace that is not properly lubricated.


These furnace problems should be taken seriously because they can cause extensive damage that may require more money to fix. If any of these sounds persist or start suddenly, call our professionals for immediate help.

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