Why Is My Furnace Making a Knocking Noise While Running?

When your furnace functions properly, it should run fairly quietly. It’s normal to hear some noise, so if your furnace is making knocking noises while running, don’t panic. However, if the noises become louder and more frequent than usual, it might be time to call Riverside's heater repair experts at Inland Empire Comfort Air Conditioning and Heating. Below, we’ve explored some of the most common reasons for knocking noises in your furnace. 

Dirty Blower Wheel

Regular maintenance always benefits your furnace, and this definitely applies in the case of the blower wheel in your furnace. If the blower wheel becomes unbalanced, you may hear knocking sounds when the furnace runs. Calling in a professional to clean and rebalance the blower wheel not only saves you from more costly repairs, but in a worst case scenario, an unbalanced blower wheel may explode. 

Keeping your furnace’s blower wheel clean is easy with regular visits from experienced HVAC furnace technicians for maintenance. Additionally, the easiest way to keep your blower wheel clean is by frequently changing your furnace filter.

Filters collect dust, hair, and other debris from the air, and gunk can begin to build up on the blower wheel. Replacing your furnace filter every three months helps avoid this, while pet owners should replace their filters about once a month. 

Ducts Hitting the Walls

Because the ducts in your heating system circulate both warm and cold air, they undergo expansion and contraction. As the metal parts of the ducts warm up, they move around a bit and cause banging noises. In most cases, these noises are normal. However, if you notice that the banging continues or other heating issues arise (like a lack of warm air coming from the vents), it may be time to call an expert furnace and duct servicing company to inspect your heating system.

While noisy return ducts generally aren’t a cause for concern, they may indicate poor installation. Your repair technicians can inspect your heating system, checking the ducts and making any adjustments necessary to eliminate the noise.

Broken or Cracked Fan Belt 

If your fan belt cracks or breaks, it strikes the metal parts of your furnace as it rotates, causing knocking and banging noises. As with any type of malfunctioning part, quick action to repair or replace the broken piece helps to keep a minor issue from becoming more serious and more expensive. 

As a homeowner, you can identify a broken or cracked belt in a couple of ways. First, listen carefully to the furnace. The knocking sound resulting from a broken fan belt has a distinctive, almost rhythmic pattern. If the banging occurs at regular intervals, the fan belt may be the culprit.

You may also want to remove the front panel of your furnace and carefully see if you detect a crack or break in the belt. In all cases, it’s best to call in a professional HVAC technician to repair the problem, so that you know it’s done safely and correctly. 

Call Inland Empire Comfort Air Conditioning and Heating for Expert Furnace Repair

When you call Inland Empire Comfort Air Conditioning and Heating, our experienced furnace technicians come out to your home and inspect your furnace, ductwork, and connections. We diagnose the problem and let you know why your furnace is making a knocking noise while running.

Because we’re Riverside’s heater repair experts, we then answer your questions and offer advice for next steps. Once you’ve decided on a course of action, we perform the necessary repairs and get your heater up and running again. We offer 24/7 service, so you know we’ll be there to handle any furnace emergency. 

Riverside’s Choice for Superior Heating and Air Conditioning Services

At Inland Empire Comfort Air Conditioning and Heating, we’re proud to serve the residents of Riverside and the surrounding areas. Our commitment to quality means that our professional technicians know all the ins and outs of repairing, maintaining, and replacing furnaces.

We care about our community and make it our goal to provide every customer with personal, customized service. Whether your furnace is making a knocking noise while running or you need to repair a cracked furnace heat exchanger, the experts at Inland Empire Comfort Air Conditioning and Heating have you covered. 



Let us ensure that your heating system functions at its peak all season long. Call Inland Empire Comfort Air Conditioning and Heating in Riverside, CA today at (951) 336-1892 to schedule an appointment.