A working furnace naturally makes a dull background noise as it heats up your house. But if your furnace starts making a loud noise when it kicks on, runs, or shuts down, you may be wondering what’s going on.

Figuring out why your furnace is making a loud noise requires some sleuthing. Your first step? Paying attention to the type of noise you’re hearing. The five noises that could be a red flag that your furnace needs a tune-up include:

  • Banging
  • Rattling
  • Squeaking
  • Buzzing
  • Whistling

In this article, we’ll go over possible reasons you could be hearing each type of noise, as well as solutions for each problem.

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Noise #1: Banging

If you hear a loud banging noise coming from your furnace, the root cause depends on if you hear the noise when your furnace is:

  • Starting up
  • Running or shutting down

When the noise occurs at start up, that typically indicates that your gas furnace is struggling to ignite. Normally when you turn on your gas furnace, gas is produced then ignited. However, if your furnace doesn’t ignite right away, the gas builds up and causes a banging or popping noise when it eventually ignites.

On the other hand, banging noises happening when your furnace is running and/or shutting down could be due to your air ducts. If there is an issue with your air ducts, such as poor airflow or incorrect duct sizing, the ducts may expand or contract as air passes through.

The solution: If your gas furnace produces a banging sound when it starts up, contact a professional to diagnose and correct the problem.

If you hear the noise when your furnace is running or shutting down, you might want to take a look at your air filter and air vents. Replace the air filter if it’s dirty and make sure your air vents aren’t obstructed. Contact an HVAC technician to inspect your ductwork if you still hear the banging noise.

Noise #2: Rattling

Do you hear rattling coming from your furnace? If so, you could have loose parts in the access panel, blower motor, or ductwork.

In some rare cases, you may have a crack in your furnace’s heat exchanger. This is the part of your furnace that heats the air that is blown out. If this part of your furnace cracks, your system could emit dangerous gases like carbon monoxide. Keep an eye out for other signs of a cracked heat exchanger such as abnormal smells and water around your furnace.

The solution: Fixing the rattling noise could be as simple as tightening a screw—or as complicated as replacing a cracked heat exchanger. If you believe you have a crack in your heat exchanger, consult a professional as soon as possible.

Noise #3: Squeaking

If you hear a funny squeaking sound coming from your furnace, it’s probably not because you have a rodent in your house. Generally, you can thank your furnace blower for this type of loud noise.

The blower fan is the part of your furnace that circulates warm air throughout your house. If you have a squeaky furnace blower, you may also notice that the air it blows out isn’t as warm as it should be (which drives up your gas or electric bill).

There are two parts of your furnace blower that could be behind the squeak: the blower motor bearings or fan belt. If either of these is worn or damaged, you’re saddled with the noise until you can get someone to fix it.

The solution: Worn or damaged belts or blower motor bearings require replacements. If the loud noise coming from your furnace is a squeaking sound, it’s time to call a professional to replace the belt or bearings.

Noise #4: Buzzing

If you hear a loud buzzing when your furnace runs, you may have an electrical issue on your hands. Furnace-related electrical problems could be due to a number of issues, such as a:

  • Loosely mounted or failing transformer box
  • Failing blower motor or capacitor

The solution: Electrical issues require a professional. If your furnace is making a loud buzzing sound while running, contact a trained HVAC technician.

Noise #5: Whistling

Hear a whistling noise emanating throughout the house as your furnace runs? More than likely, this is due to air not being able to freely pass through.

Disrupted air passage can be due to a number of issues, such as:

  • A dirty air filter
  • Blocked return or supply vents
  • Issues with your ducts

The solution: Unless you have an issue with your ducts, you may be able to quiet the whistling in your house on your own. Check to make sure your air vents are open and not blocked off by furniture. If that doesn’t solve the issue, sneak a peek to see if your air filter is dirty or clogged. If it is dirty, go ahead and replace it.

If you still hear a whistling noise, you may have leaky or misaligned ductwork, which requires a professional to seal or replace.

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Diagnosing furnace problems can be difficult—and stressful. If your furnace is still making a loud noise, it might be time for a professional’s touch. Contact Roy’s. Our trained HVAC technicians have been taking the stress out of furnace repairs since 1974.

With 24/7 emergency support and same-day service, you can count on Roy’s to get your furnace up and running.

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