Is the Loud Banging from Your Furnace a Safety Concern?

Most homes locate their furnaces well away from the main living areas, typically in a utility closet, crawl space, basement, or attic. As a result, you usually can't hear any noises from your unit when it turns on. At most, you'll probably hear the whoosh of air through your vents once the blower motor engages and warm air cycles through your house.

Of course, the fact that your furnace stays mostly out of sight and out of mind can make it all the more troublesome when it starts producing disturbing noises. What does it mean if you can hear your furnace banging when it turns on? Should you be concerned about the safety of your furnace? Keep reading for some likely answers.

Why Is Your Furnace Banging?

There are typically two reasons why your furnace might make a loud banging sound when it first turns on:

  • Delayed ignition
  • Blower motor or capacitor Issues

Fortunately, it's relatively easy to tell which might be causing your issue. Since your furnace starts in stages, the burner will come on before the blower engages. If you stand close to your furnace, you will first hear your draft inducer motor turn on, followed by the burners igniting, and finally, the main house fan turning on.

If the bang occurs as your burners ignite, the problem is delayed ignition. This bang occurs when the burners ignite late, allowing gas to build up in the combustion chamber. The excess gas creates a small explosion that produces a bang. If you've ever struggled to light a gas stove only to have the flame momentarily jump out, you've experienced a similar situation.

On the other hand, the problem is likely your blower if you hear the noise after the burners ignite. In these cases, the bang may sound more like a metallic rattling or shaking when you stand near the furnace. Numerous mechanical or electrical issues can cause your blower to make a banging, rattling, or grinding noise as it starts.

Is a Banging Furnace Dangerous?

A banging fan isn't dangerous, but it's an issue you'll need to address since the problem may be causing ongoing damage to your furnace's blower motor. However, delayed ignition can be a safety hazard. Although your furnace's flame sensor should prevent too much gas from building up, sudden ignition can potentially damage other components in your furnace.

If you hear these noises, the best course of action is to shut your furnace off using the switch near the unit and call a heating repair contractor. Although neither situation is likely to cause an immediate safety hazard, it's better to err on the side of caution and fix the problem rather than risk further damage to your furnace.