Skip to main content

Rated: 4.9 / 5 based on 2100+ reviews. Read our reviews

Deal Of The Day! $79 Water Heater Flush Get a free quote

Knocking Sound in Furnace Vents: Should You Be Worried?

Cassie Pound, owner of Quality Heating, Cooling, Plumbing & Electric
Published by
Cassie Pound
December 10, 2022
Knocking Sound in Furnace Vents: Should You Be Worried?

To diagnose and fix a knocking sound in furnace vents, call Quality Heating, Cooling & Plumbing at (918) 212-0122! 

By design, a properly functioning furnace should heat without making too much noise. Hearing a furnace vent knocking sound is rarely a good sign. Causes can range from cold weather, poor installation, damaged parts, and more. 

Homeowners shouldn’t panic if they hear strange noises from their furnaces. However, they also should pay attention to these noises as they can indicate serious problems. 

This blog will explore common reasons why your furnace makes a knocking sound and when to call Tulsa’s heating and cooling experts

Reasons Why Your Furnace Is Making Sounds 

Homeowners will find a multitude of reasons why their furnace makes a knocking or rattling noise: 

Cold Weather Is Stressing Out Your Furnace 

Naturally, homeowners use their furnaces more during winter. During winter, your furnace assumes enormous responsibility and works harder, especially if you haven’t turned it on in a long time. 

This extra effort can cause your furnace to create a knocking sound. While the sound can be a nuisance, it isn’t something to worry about, especially when battling low temperatures. 

How Can You Tell That Cold Weather Is the Problem? 

The problem with attributing cold weather to a knocking sound in furnace vents stems from the fact that you use your furnace the most during winter. As such, winter becomes the time you will most likely experience issues. 

You may hear strange noises upon turning on your furnace, but they go away after a few minutes. In this case, you can likely blame the cold weather. However, if knocking persists, you may have a more significant issue on your hands. 

You Have a Dirty Blower Wheel 

A filthy blower wheel can make it unbalanced. In the worst scenario, an unbalanced blower wheel may even explode. Not regularly maintaining your blower wheel leads to this imbalance. 

Maintaining your blower wheel is an easy fix that many homeowners can handle. Replace your furnace air filters regularly, as they can quickly suffer from buildups from dirt, debris, pet dander, etc. All this grime causes an imbalanced blower wheel that’ll eventually break. 

Our experts recommend you replace your furnace filter at least once every three months. However, you may need to replace your filter sooner. For example, we recommend pet owners replace their filters once a month. 

Cleaning Your Permanent Air Filter 

Instead of disposable air filters, some homeowners may have a permanent air filter. A permanent air filter can translate into massive savings, but you must know how to clean one properly. You’ll need filtered water, mild dish soap, and a spray-on cleaner. 

Soak your filter in your solution, then rinse off using your filtered water. Depending on how much dirt and grime, you may need to repeat this process several times. 

You can let your permanent filter air-dry, but you won’t cause harm by placing it back inside your furnace immediately.  

Your Air Ducts Are Striking the Walls 

Inside your air ducts, two processes occur—contraction and expansion. As temperatures rise, your air ducts’ metal parts heat up. These parts will then move around, producing a knocking sound in furnace vents. 

Fortunately, this is entirely normal and generally doesn’t signal an issue. 

How Can You Tell Your Air Ducts Are Causing the Noise? 

Like cold weather, a knocking sound caused by air ducts occurs when you first turn on your furnace. However, a knocking sound caused by air ducts can also appear when your system stops blowing warm air. 

While noisy return ducts generally aren’t a cause for concern, they can indicate poor installation. An expert HVAC technician can inspect your system and make adjustments to kill the noise. 

Your Fan Belt Is Hitting Other Components 

A broken or cracked fan belt will strike your furnace’s metal parts as it rotates. Therefore, you must replace a cracked or broken fan belt when you identify the problem. Doing so will prevent harm to other crucial parts. 

Identifying a Broken or Cracked Fan Belt 

The first way to identify a cracked or broken fan belt includes removing your furnace panel. However, you can also identify this issue by carefully listening. 

A knocking sound in furnace vents from a broken fan belt has a distinctive pattern. You probably have a broken fan belt if you can easily predict when the subsequent knocking occurs. 

Can You Fix a Fan Belt Yourself? 

For some homeowners, a broken part allows them to test their DIY skills. However, repairing a broken fan belt requires a specialized touch. It’s better to call a professional HVAC technician to avoid further damage.

Ways To Help Choose the Right HVAC Technician for the Job 

Whether dealing with dirty burners, exploring open versus closed vents, or diagnosing why you hear a knocking sound in furnace vents, you need to hire the right team. The following steps can help you make your selection: 

Do Ample Research 

While online reviews can be a great start, referrals from trusted sources often carry a higher weight. You should also check a contractor or company’s website and social media pages. Look for the following elements: 

  • Their qualifications 
  • A licensed, insured, and bonded company 
  • Their core values 
  • What types of clients do they serve
  • If they specialize in any areas
  • Testimonials 

Request an Estimate

Many HVAC repair companies provide a free estimate. State your problem and ask them how much the service will cost, alongside an average timeframe. 

An On-site Visit and Consultation 

Finally, your HVAC repair technician will visit your home or business and inspect your system. Once they diagnose the issue, they may need to adjust the initial estimate. Once you agree with the price, they can start working or schedule a future time. 

Call Our Team Today 

Dealing with a knocking sound in furnace vents can be annoying. However, our Quality Heating, Cooling & Plumbing team can troubleshoot the problem and provide affordable repair options. 

To discover the answer to “How do I know my furnace control board is bad?” Tusla, OK, residents can call us at (918) 212-0122!

Cassie Pound, owner of Quality Heating, Cooling, Plumbing & Electric
Published by
Cassie Pound

Cassie Pound is the Vice President of Quality Heating, Cooling, Plumbing & Electric with locations in Tulsa, Glenpool, and Bartlesville, Oklahoma.