Why is my Furnace Making Knocking Sounds?


Why is your furnace making a loud noise when it turns on? There are a few possible reasons for a noisy furnace. The fan might need repaired, the blower wheel might be unbalanced, or the inducer fan motor might be on its last leg. We’ll explain each possibility.

Common Reasons for Knocking from Furnace

The Fan is Going Out

If the fan is the cause of the noises, there’s a good chance that something is caught in it. Our technicians have found paper, tin foil, and even birds in furnace fans. Any of those things will make it noisy. Sometimes, having it cleaned by an HVAC professional takes care of it, but if the fan is damaged or old, it needs to be replaced.

The Blower Wheel is Dirty

Have your HVAC company make sure the noise isn’t caused by the blower wheel. An unbalanced blower wheel can explode. But what makes a blower wheel get unbalanced?

The most common reason for an unbalanced blower wheel is a lack of maintenance. By that, we mean that the furnace filter either hasn’t been changed in a long time or there is no filter. In either case, dirt, crud and pet hair builds up on the blower wheel. This puts it out of balance, causing obnoxious banging noises. Eventually, the wheel breaks down completely.

It’s easy to avoid this problem by regularly changing your furnace filter. Our HVAC technicians suggest replacing the filter once every three months or as soon as it’s no longer a clean white color. If you have pets in the house, you need to change it every month. Pet hair clogs the filter, and a dirty filter will do a number on your furnace.

The Inducer Fan Motor is Failing

Maybe it’s not banging and knocking you’re hearing in your furnace. Maybe it’s an annoying squeak. If that’s the case, then it’s probably caused by the inducer fan motor. It squeaks and makes noise when it needs to be replaced.

What’s the bad news? A noisy furnace is almost always a sign that some kind of maintenance needs to be done. The filter needs replaced and moving parts need to be cleaned or replaced. If you’re hearing weird noises in your furnace, that baby needs some TLC. Schedule an appointment with TLC to get it checked out.

And the good news? The good news is that most of these problems can be avoided with regular filter changes and a yearly furnace inspection. Getting your furnace professionally inspected and tuned up – just like taking your car in for routine maintenance – can help you catch problems before they become emergencies.

Get that banging checked out. Schedule your furnace inspection today! You can also ask us a question or give us a call at 505-761-9644.