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Furnaces do make some noises. There’s the whirring of the fan, clicking of the igniter just before the burner starts up, and the movement of air inside the ducts. All these sounds are considered normal, and you’ll get used to hearing them after some time.

There are, however, some unusual noises coming from your furnace, and they should not be ignored. The unexpected pop from the furnace that did not happen before, an intermittent shriek, or even a continuous rumble heard even after the burners have stopped running. Pay attention, and it will save you money in the long run. Here’s why.

The meanings behind the most frequent furnace noises.

Banging or Booming at Startup

This is the one that will make homeowners sit up and pay attention, and they should.

A loud bang that occurs at startup is a sign of delayed ignition, meaning that gas has been accumulating inside the combustion chamber for several seconds until the ignitor sparks a small explosion inside, which results in a loud bang.

The possible causes for a banging furnace include clogged burners, faulty ignitors, or reduced gas pressure. The amount of gas that ignites simultaneously determines how loud the bang will be and increases the risk of damaging the heat exchanger.

A broken heat exchanger is not only costly but is also highly dangerous as it can lead to a carbon monoxide leak into your living space. If you experience a banging furnace, take action immediately.

Rattling

A rattle is generally one of several possible issues, from trivial to serious.

Trivial examples include: a loose furnace cabinet panel, a loosened screw, or expansion and contraction of ducts with changing temperatures. All of which should be fixed but aren’t urgent.

Serious possibilities include: a damaged heat exchanger which makes a rattling or roaring sound while exhaust gases pass through its cracks during heating periods. This issue relates to the previous one in terms of carbon monoxide danger and should be checked by a professional.

If you notice a newly appeared rhythmic rattle from inside the furnace, you should check it.

Squealing or Screeching

Any high-pitched squealing almost certainly means something mechanical, either the blower motor itself or its belt.

In older furnaces, the blower is belt-driven, and when the belt begins to crack, fray, and slip, it will cause a lot of friction that results in a squealing noise. It is easy and cheap to replace a broken belt. Allowing one to break is definitely more troublesome, especially in January.

In newer systems with direct drive, the squealing means a bad motor bearing, and you can choose between replacing just the bearing or waiting until the whole motor breaks down.

If the noise goes away after some time, the problem is likely with the bearing. If the squealing occurs throughout the operation, get someone to check the belt and the motor.

Rumbling or Humming After Shutdown

Although the furnace has stopped operating, there is still a small rumbling noise that persists for several seconds. This can be considered somewhat normal as it results from the heat and airflow remaining after shutdown. However, if there is a rumbling sound even after the burners have stopped working, it usually indicates a problem with either dirty burners or pilot lights.

With dirty burners, the gas does not fully combust. The result is that there is gas left after the initial ignition process, leading to a rumbling sound after shutdown.

Clicking That Won’t Stop

It’s normal for a furnace to produce clicking sounds when the igniter is cycling. However, it isn’t normal for a furnace to click without ignition occurring.

Failure to ignite following repeated clicking is an indication of either a bad igniter or a contaminated flame sensor that’s unable to tell if the burner flames have ignited. The furnace will attempt ignition, find that ignition didn’t occur, turn off the gas supply, and try again, continuing the process until it trips the safety lockout.

A non-heating furnace that clicks should be seen by a professional; the safety lockout is working properly but the problem still requires diagnosis.

Get Your Furnace Checked by Frozen Flame

Frozen Flame is a professional furnace repair company that provides furnace maintenance services to clients located in Guelph, Kitchener, Waterloo, Cambridge, Brantford, and Hamilton. We’d prefer to diagnose the problem through maintenance than having to do repairs when your furnace breaks down at 2AM one winter evening. In case your furnace makes an unusual noise, then give us a call right away and we will inform you about the issue.