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Why Is My Furnace Making Weird Noises?

Unusual noises are often one of the first signs of trouble with any piece of HVAC equipment. Since furnaces typically run on natural gas, strange noises can be especially distressing. If your furnace has been making sounds, then it's essential to call an HVAC professional to diagnose it as soon as possible. In the meantime, this guide will help you to identify the likely cause of the problem. If you can't find your problem listed here, or if you are unsure of the source of the noise, stop using your heating immediately until a technician can properly evaluate your furnace.


If you hear a loud bang from the furnace itself (and not the ductwork), then you may have a delayed ignition problem. If you've ever tried to turn on a gas stove that refuses to light, you may have experienced a sudden flare-up as the unburnt gas finally ignites. A similar situation can occur in your furnace. When the igniter fails to trigger the initial flame, unburnt fuel can remain in the combustion chamber. The excess of fuel creates a small explosion that you are likely to hear as a very loud bang or a pop.

Rattling or Light Banging

Your forced-air heating system uses a fan to distribute warm air throughout your house. If the blower is failing, you may be able to hear rattling or light banging noises. These are sometimes audible throughout the house if they are loud enough, but they can be transmitted through the ductwork as well. A failing blower motor often makes a distinctive sound, and if you've ever heard a fan that's on its last legs, then you will recognize the noise immediately. Although they aren't dangerous, blower problems shouldn't be ignored since the blower will eventually fail entirely.

Screeching or Squealing

Most problems with a furnace make low, boomy sounds, but there are issues that can produce higher-pitched noises, too. The blower is one of the only moving parts in your furnace, so motion-related sounds usually originate there. If you can hear metallic parts screeching against each other, then your furnace's blower is warning you about its impending failure. In some cases, the problem may be solvable with lubricant. Note that the blower motor and the fan are often separate components connected by a belt, so a squealing noise that sounds like an old car starting on a cold morning may be a worn belt.

As with most HVAC issues, the best way to avoid hearing any distressing sounds is to have your system regularly inspected by a professional. Once you do hear a noise, don't hesitate to have it diagnosed so that you can get back to enjoying a warm refuge from the frigid temperatures outside.

For more information, contact an HVAC contractor.