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Furnace Noises: What’s Normal and What’s Not Normal?

An ideal situation for homeowners in Oswego, Yorkville, Naperville, Aurora and Plainfield is to have a furnace that performs all winter long with few issues and no need for repairs. Think of how much you depend on yours when icy winds are whipping and ice and snow are building outside. Your furnace works hard to keep you in comfort and safety.

Your furnace is also made to communicate with you. When something is wrong, it will often try to tell you by making particular sounds of alert. In this discussion, we’ll review which furnace noises are normal and which are not normal.

Furnace Noises: What’s Normal

When your furnace starts up in response to your thermostat setting, you will hear the system activate. It’s a new sound that wasn’t there moments ago. This is perfectly normal.

In some cases, you might hear a click or a pop while the furnace is turning on. After that, the sound might settle into a low hum while the system rums. These clicks or pops are much like what you hear when you’re turning on a stove burner or igniting a gas grill. These noises again are normal.

If your furnace is older (e.g. 20+ years), it might be a bit louder than new models manufactured during the last decade. New furnaces often include special features and extra insulation to soften the sound they make when they run.

Another factor influencing the noises a furnace will make is the type of system it is. If your unit is a variable-speed system, you may not notice some of the minor adjustments it makes while operating. This differs from single-speed systems, which can tend to announce what they’re doing by audibly “shifting gears.”

In sum, normal noises that a furnace makes during a heating cycle are those you might expect and that do not become odd or disruptive.

Furnace Noises: What’s Not Normal

Furnace noises that are not normal are those that are sudden and unusual when your unit starts, operates or shuts down. When you hear them, you should contact a certified HVAC technician right away to inspect them.

Such noises might include:

  • shrieking or squealing. This is caused by a problem with the blower motor in the furnace. It could be something simple such as a loose or damaged belt or something much more complicated. Notify your heating professional if you hear these noises.
  • louder humming. A normally functioning furnace will sometimes make a low hum, but if the volume of it increases during a heating cycle or it appears out of nowhere, something might be wrong with the furnace’s blower fan or capacitor. Have your heating professional inspect the blower motor right away.
  • rattling and rumbling. Some malfunctioning furnaces might make a loud rattling or rumbling noise when they complete a heating cycle. This could mean that something is loose or that fuel is still burning in the combustion chamber even after the burners are off. Act swiftly upon hearing this sound, because the issue behind it could lead to the risk of carbon monoxide poisoning.
  • scraping and grinding. These not-normal furnace noises can indicate a loose blower wheel or dry or worn ball bearings in the blower motor. Turn off the system and contact your heating professional.
  • repetitive clicking. If you have a gas furnace and you hear a clicking noise when the unit starts and stops, that is normal. If the clicking continues during operation, that is not: Many times it means there’s an issue with the control panel or the compressor.
  • loud bangs and pops. On occasion you might hear a popping noise as the furnace activates. When warm air hits the ducts’ cold metal, it causes the metal to expand, which makes the popping noise. If the popping starts getting louder, it could be a sign that the furnace’s burners are dirty or that there’s a clog or a gas-pressure problem. If the burners are dirty, gas can build up in the combustion chamber until it cracks or makes holes in the heat exchanger, a serious issue that needs professional attention.
  • thumping. You may have heard the thumps and bumps of an unbalanced washing machine load before. If you hear similar noises from your furnace, they can often signal an unbalanced blower motor or wheel. This would be another urgent problem that calls for prompt repair. The blower motor and wheel are significant furnace parts that you don’t want bouncing around.
  • whistling. Restricted airflow can sometimes product a whistling noise. The culprit is often a clogged or dirty air filter, so be sure to check the filter regularly.

The Danger of No Noise

Sometimes a furnace that isn’t making any irregular sounds can still have a serious problem. In particular, a carbon monoxide leak will not have any color, odor or taste, but it can be deadly if allowed to concentrate and be breathed.

A crack in the heat exchanger is a common cause of carbon monoxide poisoning, which includes symptoms such as fainting, dizziness and nausea.

To ensure your furnace is operating safely, make a point of scheduling annual maintenance before each winter. This will help reinforce proper safety and performance throughout the heating season.

Contact Us Today

If you should ever start to hear abnormal noises such as the ones we’ve described, your comfort and safety depend on having the issue resolved. The certified HVAC technicians at Air Dynamics welcome the opportunity to answer your questions about furnace noises that are normal and not normal at your home in Oswego, Yorkville, Naperville, Aurora or Plainfield. Simply give us a call at (630) 731-1550.

If your situation is urgent, Air Dynamics offers same-day service for furnace repairs in Oswego, Yorkville, Naperville, Aurora and Plainfield. Also ask us how you can save extra money on valuable heating and cooling services with our All-Inclusive Maintenance Plan.

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