Why Is My Furnace Rattling?

Nick Durante
by Nick Durante
Credit: Shutterstock / Globalphotogroup

It can leave you feeling uneasy when you hear unusual sounds coming from your furnace. Some furnace sounds are normal, but they can also point to serious problems. So, you may ask, why is my furnace rattling?

The most common reasons a furnace is rattling are that the blower motor is damaged or the bearings are loose. Worn fan belts and loose air ducts can also cause a rattling sound when your furnace is running. Your furnace can also rattle if the heat exchanger breaks, and that’s dangerous as it can leak carbon monoxide.

Luckily, the rattling sound can also happen due to simple problems, like a dirty air filter. Always call your local HVAC service if you hear a rattling sound. It could be something simple like a loose panel, but it’s better to be safe than sorry. Follow along as we explore the most common reasons why your furnace is rattling.

Why Does My Furnace Rattle?

1. Loose Bearings

The best-case scenario when you hear your furnace rattling is that the blower motor’s bearings are loose. Over time, the frequent motion of the motor can knock the bearings loose. They will shake as your furnace runs, and the sound can be quite annoying.

The bearings can also become loose and rattle if they are corroded. Many components of a furnace are susceptible to corrosion because of the heat and humidity. Luckily, this is a cheap and easy fix, as an HVAC professional can quickly replace the bearings.

2. Damaged Blower Motor

The blower motor is one of the most essential parts of a furnace system. Blower motors can crack or become dislodged over time. They are also susceptible to corrosion, especially if your house is humid.

Unfortunately, you cannot typically repair a damaged blower motor in most cases. Instead, you must replace the part entirely for your furnace to run efficiently. It costs an average of $550 to replace a blower motor, but it can cost as much as $1,200.

The cost ultimately depends on what type of furnace you have and how long it takes to fix the problem. HVAC professionals typically charge an hourly rate of $75-$150 or more. This adds up quickly and is the biggest cost factor when it comes to furnace repairs.

3. Worn Fan Belt

A worn fan belt will rattle or squeal as your furnace runs. Luckily, this isn’t a major problem and is typically easy and cheap to replace. Worn fan belts aren’t repairable, but you can replace them for $125 or less.

4. Broken Heat Exchanger

A broken heat exchanger can explain the rattling noise when your furnace runs. This may be an annoying sound, but it’s also a dangerous sign. When a heat exchanger cracks, it can leak carbon monoxide into your home.

This is an emergency, and you must call an HVAC professional right away. That said, most homeowners may not be familiar enough with heat exchangers to diagnose the problem. Because of that, it’s a great idea to schedule a furnace inspection if you hear a rattling sound.

It may be something simple, like loose bearings. However, it’s not worth the risk of carbon monoxide poisoning in case it turns out to be the heat exchanger.

5. Loose Air Ducts

Many people jump to the conclusion that the rattling sound is within the furnace itself. While that is often the case, the sound can also come from your ductwork. Air moves through the ducts, and it’s typically a quiet process.

However, you will hear the ducts rattle when air moves through them and they become loose. Over time, corrosion and gravity take a toll on your home’s ductwork. They can eventually sag or loosen over time, and they will bang and rattle as air moves through the ducts.

Luckily, this is something that any HVAC professional can fix. It may take a while and be costly if they must open your walls or ceiling to access the ducts. However, it’s worth the cost, as your air ducts will only sag more if you don’t fix them.

6. Dirty Air Filter

Do you change your air filter every 30-90 days? If not, that could explain why your furnace is rattling when it runs. Clogged air filters make it hard for air to pass through your HVAC system.

Not only does this affect your system’s performance, but it will also increase your energy bills. Your furnace must work harder, but it also won’t be as effective. Because of that, many people compensate by cranking the furnace higher, and this will lead to pricey bills.

Air filters that are caked with debris can create pressure within your HVAC system. The harder it is for air to pass through the filter, the noisier it will be. In some cases, this can result in an unpleasant rattling sound. You can easily replace the air filter without hiring professional help.

7. Dirty Burners

Every part of your furnace contributes to its performance. The burners are essential, but they can also be quite noisy if they are dirty. No matter where your furnace is, it is susceptible to dirt and dust that can ultimately damage the system.

One sign that the burners are dirty is that the flame is weak and yellow. Another sign is that your furnace rattles when it starts. This is a potentially serious problem, as explosions are possible when burners are overly dirty and clogged.

The explosion can damage the heat exchanger, and carbon monoxide may leak into your house. You should never try to clean your burners. It’s too easy to accidentally damage the gas lines, and that’s quite dangerous. Instead, call your local HVAC service.

8. The Panel Isn’t Tight Enough

The simplest and easiest to fix reason your furnace is rattling is that the panel isn’t tight enough. This can happen if you simply open it and forget to close the panel all the way. Many homeowners and even HVAC professionals leave the panel slightly ajar after inspecting the system.

In this case, all you must do is push it tight all the way. Call an HVAC professional right away if your furnace keeps rattling after you push it tight.

When Should I Worry About My Furnace Noise?

You should worry about furnace noises if your carbon monoxide detector goes off, or if your bills are unusually high. This can point to a broken heat exchanger, and it can be potentially deadly. It’s always worth calling an HVAC service professional if you hear rattling, squealing, or grinding noises when your furnace runs.

Even clicking and popping noises can be a bad sign. That can point to dirty burners, which in extreme cases, can eventually cause a small explosion.

Summing It Up

If your furnace is rattling, it is likely because of loose bearings or a damaged blower motor. The rattling sound can also come from a worn fan belt or broken heat exchanger.

It’s important to know that a broken heat exchanger can cause carbon monoxide to leak into your house, and that can be fatal. Otherwise, the sound could be due to dirty burners, a clogged air filter, or loose air ducts.

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Nick Durante
Nick Durante

Nick Durante is a professional writer with a primary focus on home improvement. When he is not writing about home improvement or taking on projects around the house, he likes to read and create art. He is always looking towards the newest trends in home improvement.

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