What Causes a Furnace to Make Knocking Sounds? – Noise Solutions
What Causes a Furnace to Make Knocking Sounds? – Noise Solutions

What Causes a Furnace to Make Knocking Sounds? Stop being concerned and take action! Lots of heating systems can produce annoying noises, like gurgling or knocking sounds coming from a boiler or radiator, but some can be a warning of danger. Old furnaces rarely made running water or gurgling noises because there was no condensation or liquid involved. Today, newer and higher-efficiency furnaces inevitably produce condensation as they are “condensing” boilers. They are more energy-efficient, however, the increased sophistication may cause noise problems.

All heating systems make some kind of noise. Radiators make knocking and hissing sounds, and even a small ductless system will hum a little. Furnaces will make a low hum or rumble while operating normally.

One of the most common oil furnace problems is the unusual sounds they can make when they aren’t performing as well as they could. Knocking, rattling and squealing are just some of the noises that indicate something is wrong.

When to Replace Furnace Belts

If the sound is coming from your furnace and not from a tormented soul! It’s probably because a motor belt slipped off its track. There are three main causes for a squealing sound:

  • loose-fitting and
  • fraying blower belts,
  • don’t try to adjust or replace your furnace blower belt on your own (this should always be performed by a qualified technician).

Image text: "What Causes a Furnace to Make Knocking Sounds?".


How to Troubleshoot Home Furnace Blower Problems

Type of noise: screeching
your furnace blower is what pushes warm air through your ducts and into your home. It needs proper lubrication in order to work properly. If your blower motor isn’t properly oiled – much like the tin man in the wizard of oz – it’ll cause problems for the rest of your furnace.

Sometimes popping noises coming from the furnace are carried into the home through the ductwork. If you have recently had a new furnace/system installed and the popping noises are new, there is a chance that your ductwork may need some repairs to make it compatible with your new system.

If a loud boom occurs within seconds after a gas furnace begins its cycle, often before the blowers kick on to distribute air through the ducts, the furnace may have a more serious problem. The ignition system may not be firing correctly, so gas builds up in the burner before the pilot light ignites it. This is often due to dirty burners.

Furnace draft inducer blowers push air and gases out of your furnace and towards outside, improving the quality of the air that moves through your furnace. A furnace inducer motor noise can be one of the main problems homeowners experience with this component, which is mostly found in newer, high-efficiency furnaces.

What Are the Causes of a Gas Furnace Blower Motor Not Shutting Off?

If your furnace is making a weird noise here are a few possible causes:

  • the furnace is making a whining noise
  • the most common cause of whining furnace noise is a damaged blower motor.

Based on how badly it is malfunctioning, either fix it or replace it.

Troubleshooting a Furnace Duct: for Banging Noises

Banging or squeaking when you walk on the floor near the furnace can happen. The duct could be on too tight or the metal panning is not nailed-in correctly. This can be easily fixed by doing one of the following:

  • reinforce the duct with an oil-canning duct
  • rehang the duct
  • replacing it with a thermo-pan, a better quality sheet metal.

The noise may not be coming from your furnace at all. In some cases, if ducts become unsealed, misaligned or improperly installed, the changes in heat and airflow can cause them to sway or resettle, resulting in banging noises throughout your system.

If the noise is coming from inside your home

The furnace in our house is not too old but is not new either. Maybe like 10 yrs old I’d say the filter has been replaced, within the last month, it is in good shape. However, since we moved in I noticed a banging noise (with up to 3 separate bangs when the furnace shuts off.

This sound often indicates a motor is close to burning out. You may also notice an acrid smell coming from the vents along with the noise. Have repairs done as soon as possible, the motor will probably need to be replaced.

What causes the noise can be hard to decide. You may have a hard time knowing where the bubbling/gurgling sound is coming from, but it’s most likely related to a refrigerant leak. A gurgling sound could also mean that your condensate drain line is clogged.

Why is my furnace making a loud noise? Usually, homeowners don’t give their air conditioner or furnace much thought as long as they’re working correctly. It’s not until there’s banging or another loud noise coming from the vicinity of the HVAC system that you start to pay attention.

If the noise is coming from outside your home

Hearing a hissing noise most likely means air is escaping from your system. If the noise is coming from the walls, there’s a good chance your ducts are leaking. Not only can this cause noise, but it also wastes money because the air that should be circulating throughout your home is leaking into the walls.

Aside from making noises, there are other problems that can occur when firing up your heater for the first time. Initially, you might notice a burning smell coming from the air vents in your home with conventional and packaged systems.

You may hear a crackling sound coming from the ducts or furnace just after your furnace turns off. This is a normal sound associated with cooling ducts and other metal parts. Pay attention to the timing of the sound.

Loud noises coming from a home ac unit are not normal—these units are designed to operate quietly, with noise barely above a whisper level for those inside the home. A loud knocking noise is usually a sign that something is wrong with your AC unit.

Why Is There a Bang When My Furnace Turns On or Off?

I have a slightly older style bathroom sink faucet, the style that you pull the knob up to turn on and adjust left or right for hot and cold. When I push it back down to shut the water off, it makes a clunking sound.


If your heat pump sounds like it’s vibrating, there are several potential problems, some of which are an easier fix than others. You can try placing rubber pads under the unit to absorb vibrations and reduce the noise. You should also check to determine whether the piping for the refrigerant is strapped too tightly.

New heater makes a noise when fan/heat shuts off

So we had a new gas heater installed this past summer. What is it that causes a furnace to make knocking sounds? The technician has been out twice now to fix what is described to me as a problem with the sheet metal flexing when the heater and fan shut off. Further problem solving for a furnace that makes a banging noise when it shuts off is available at wppts.com/furnace-makes-banging-noise.

Causes a Furnace to Make Knocking Sounds

You could have an urgent issue on your hands if you’re noticing your furnace making a knocking or banging noise. If your furnace is making a knocking noise, it might signal there could be a couple of problems. These involve gas building up in your furnace or a ductwork issue.

The changes in pressure inside the ducts will cause the sheet metal ducts to “pop”. You may see that some of the ducts that have a large surface area have a break in the surface that goes from one corner to the opposite corner.

You could have a critical issue on your hands if you’re hearing your furnace making a banging noise. If your furnace is making a knocking noise, it might signal there could be a few problems. These involve gas increasing in your furnace or a ductwork issue.

You may have an urgent problem on your hands if you’re noticing your furnace making a banging noise. If your furnace is making a knocking noise, it might mean there could be several problems. These include gas increasing in your furnace or a ductwork situation.

Furnace Making a Buzzing Noise

If you hear your furnace making a buzzing noise, don’t delay calling a HVAC expert or plumber. Of all the possible faults which cause a furnace to make knocking sounds, a buzzing sound often is telling you there’s an electrical problem, like with its transformer, blower motor or capacitor. Your furnace depends on an internal transformer to run on the proper voltage.

If your furnace is making a rattling noise, it could be due to something minor, like a loose screw, or something critical, like a broken piece. In either case, we recommend shutting off your furnace and calling a heating specialist for assistance.

The post What Causes a Furnace to Make Knocking Sounds? – Noise Solutions appeared first on GQ Central.



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