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Differentiating Normal and Unusual Furnace Noises

Normal furnace noises

Furnace Noises

Every mechanical item makes some kind of a noise when it works. When it comes to a furnace, the noises should be quite noticeable. However, if you start hearing weird, strange, or unusual noises coming from your furnace, it might indicate a problem that needs your attention. The experts at King Heating, Cooling, and Plumbing are here to explain what furnace noises are normal and which ones signal the need to call an experienced technician for assistance.

Normal and Usual Furnace Noises

Some of the noises your furnace makes are entirely normal. Here we will discuss what seemingly unusual noises are normal and other sounds you don’t have to worry about.

1. Popping from Ducts

When the thermostat signals the furnace to fire up, the blower fan responds and begins pumping warm air through the ductwork. The subsequent increase in air pressure inside the ductwork can result in a pinging or popping sound. Thus, you don’t need to worry about them.
Such sounds will be more observable if you have installed new ducts or recently cleaned your existing ones.

2. Chirping

Some chirping noises at the start of a heating season are quite normal. This usually happens if you haven’t used the system in a long period. Nevertheless, the noise is likely to go away as the furnace runs for a while. In case the noise doesn’t go away, all your furnace needs is a little routine maintenance.

3. Humming

Older furnaces are slightly louder as compared to newer ones. This is because newer ones are usually designed with added insulation and special features to minimize the noise you hear as it works. The usual sounds a furnace produces in a heating cycle shouldn’t cause disruption inside your house.

Worrisome Furnace Noises

Here are some furnace noises you need to watch out for as they can point towards problems that require immediate attention.

1. Banging

If your furnace is making a loud banging or booming noise, the problem might be due to a gas explosion that occurs if there’s a delay in ignition. Gas can build up inside your combustion chamber when the gas burners in your burners fail to ignite on time. In case the gas burners don’t ignite efficiently, this indicates a gas pressure issue or a clog.

Don’t try to repair a gas burner without the help of a certified technician. Disassembling the burners or heat exchangers can result in a gas leak in your home.

2. Shrieking

High-pitched shrieking or squealing sounds are due to a problem with the furnaces blower motor. A loose belt is a common problem. However, the issue might be more complex within your blower motor.

3. Scraping and Grinding

Scraping and grinding furnace noises are usually a sign of dry or worn-out bearings inside the blower motor. Such bearings have to be lubricated regularly to maintain effective and proper function.

Another reason behind such noises might be the loosening of the blower wheel. It is best to switch off the heat and call a licensed HVAC professional.

4. Rattling

If a part gets loose in your furnace, it will lead to vibration. This can eventually break other components in your electric or gas furnace. Get in touch with a technician to inspect the hot surface ignitor, blower motor, gas burners, or heat exchangers. A professional has the equipment and tools needed to tighten up the loose parts in your furnace.

5. Rumbling

A loud rumbling through your house should be concerning. It can be because the fuel is burning inside the combustion chamber even when the burners are turned off.

Other possible issues include problems with pilot lights, flame sensors, or burners. One important reason why you need professional HVAC intervention is that such a situation significantly increases the likelihood of carbon monoxide contamination and poisoning.

6. ‘Thwapping’

This sound can indicate that something is stuck in the blower’s fan blades. An easy way to confirm this problem is if the noise comes and goes with the airflow.

Even though this situation might not be critical to the ongoing function of your machine, the obstructing object might be causing unnecessary damage to the unit.

7. Whistling

Your furnace might be a whistling sound because of restricted airflow due to a blocked air filter. You can change your air filter to see if the noise goes away.

8. Popping

At the start of a heating cycle, the blower motor blows warm air into the air ducts in your home. If you hear loud popping noises when you activate the furnace, the problem could be inflation in your air ducts. After the warm air reaches the cold air ducts, the metal is going to get enlarged.

Conversely, the source of the popping sound might be contaminated gas burners in the furnace. When the furnace in your home gets older, sediment starts to collect on the burners. If you don’t remove the debris from the gas burners every year, a large amount of gas will start collecting. This can lead to holes in your heat exchanger.

9. Thumping

Bumping and thumping noises often indicate an unbalanced motor wheel or blower. This is a major issue that necessitates immediate HVAC repair. The motor and blower wheel are important parts of your furnace, and you really don’t want them bouncing around.

10. Humming

Several furnaces are going to make a low humming noise. However, if this sound is becoming unusually loud, it’s a sign of a serious issue with your capacitor or blower fan.

11. Frequent Clicking

Gas furnaces make a clicking sound when a heating cycle begins and stops. This is quite normal. However, you hear the clicking sound over the course of a heating cycle; it is generally indicative of a control panel or compressor issue.


If you notice unusual, strange, or weird furnace noises, it’s best to turn off your heating system and contact King Heating, Cooling, and Plumbing for furnace repair. Our friendly, certified HVAC professionals offer 24/7 emergency service at no extra cost.