What Is That Noise Coming From My Furnace?

December 06, 2018

You've been using your heat more as the weather gets colder, and you might’ve noticed some noises that seem to coincide with the furnace kicking on. These might be nice and quiet sounds, like the low steady hum of fans and motors, or air whooshing through your vents. However, there may be other noises coming from your heating system that are not in the “nice steady hum” category, and they may indicate a problem that needs investigation. If you’re wondering, “Why is my furnace making a loud noise?” read on to learn the answers. 

You hear a scraping noise 

Let's just say scraping sounds are not good sounds when they're originating from your HVAC. A scraping noise usually means something is wrong with the fan blades and/or motor. If you hear something that sounds like screeching or scraping, turn off your heating equipment right away. A foreign object may be obstructing your blower, or one of the fan blades may be warped or broken. In either case, it can cause your motor to burn out. You'll need to call a technician to inspect your furnace and correct the problem.

You hear a thumping noise 

Things that go thump in the night or any other time mean something is out of balance. Thumping sounds that come from your furnace could indicate that a motor or blower wheel is out of balance. This could cause big problems for your mechanical equipment down the road. It's best to have an HVAC professional take a look - and fix a small problem before it becomes a big one.

You hear a rumbling noise 

A low rumble is a normal sound when your gas or oil-fired furnace kicks on. However, if that rumble is louder than usual - or lasts longer than usual - this could indicate a very serious problem with your burner. If you hear a loud or long rumbling noise coming from your gas or oil furnace, turn off your equipment and call for service.

You hear a rattling noise 

A rattling noise coming from the furnace could mean that fasteners to the metal housing of your heating unit have worked loose. That's not usually a serious issue, and those fasteners can be easily tightened. However, if the rattling noise is coming from inside the unit, that's another matter altogether. You should call a technician to see if the problem is serious. Sometimes twigs and other outdoor items can get inside the fan of an outdoor unit, causing a little clanking or rattling around. If you can see this is the problem, you can just switch off the power and remove the debris. If you see the debris has somehow caused damage to the compressor or fan, call a technician.

You hear a popping noise 

Popping sounds are quite common when you turn on your furnace at the beginning of the heating season. This is usually the sheet metal in your ductwork responding to pressure -- popping one way in reaction to the negative air pressure of the fan, then popping back when the fan shuts off and the pressure releases. It's not usually a worrisome noise unless it becomes very loud or very persistent. In that case, you might want to have your ductwork inspected.

You hear a hissing noise 

If you're hearing a hiss, you're likely hearing escaping air. This could be caused by an improperly installed air filter, or one that is the wrong size. Often having too many closed vents, or having furniture blocking air flow can be the cause of a hissing sound. If the hisses become very loud, it could indicate there is a leak somewhere in the ductwork – and that means a lot of expensively heated air is escaping where it can’t be used. Again, if this is the case, you’ll want to have your ductwork inspected.

You hear a whistling noise 

Whistling noises coming from your HVAC equipment could mean there's a refrigerant leak in your condenser, or some other problems that are causing internal pressure. If you hear a whistling sound coming from your furnace, call for a service technician.

Common Questions About Furnace Noises

Should a furnace make noise?

The answer is yes, but that doesn’t mean the sounds it makes are all healthy. Here are some frequently asked questions homeowners ask our experts about strange furnace sounds and how to resolve them.

What DIY steps can help me identify and fix minor furnace noise issues?

Keep in mind that working on your furnace yourself could void the manufacturer’s warranty, and if you don’t know exactly what you’re doing, it can be dangerous. Call a professional if you’re unsure about anything. 

When you inspect your furnace unit, be on the lookout for these potential issues that can cause noises: 

  • Check your air filter for loose components that might cause clicking
  • Inspect the blower motor for signs of banging or misalignment
  • Examine the burner and pilot light for irregularities such as dirt buildup
  • Tighten any loose screws, bolts or fan blades to resolve rattling or clanking 

If the humming, clicking, banging or buzzing you notice start to intensify, call for professional HVAC contractors who can find and resolve the root causes for you. 

What safety precautions should I take before checking out my furnace?

Before you do any probing into your HVAC unit, make sure you will be doing so as safely as possible. This means switching off the power to the furnace. Don’t attempt to put your hand or fingers inside the furnace unit to avoid making contact with hot or sharp components. Pay attention to the signs of a potential gas leak, such as rotten egg odors, hissing sounds or dead plants in the area. If you notice any of these, evacuate the house right away and call for professional help. 

Do temperature changes or humidity affect the sounds my furnace makes? 

Environmental factors such as temperature or humidity changes can contribute to your furnace making noises. When it gets cold, the metal components can contract, causing popping or clicking sounds. High humidity can cause rust, which leads to squealing or grinding noises. Call a professional HVAC technician if you notice any of these signs.

Can certain furnace noises be a sign of inefficient operation? 

Yes, some sounds may indicate your unit is not operating at peak efficiency, which can lead to higher utility bills. For example, a loud bang might mean the furnace is suffering from delayed ignition, which wastes gas. Whistling or whining might be a sign of a clogged air filter, which forces the unit to work harder. Humming and buzzing sounds could signal a faulty blower motor or capacitor, which means more energy is consumed than is necessary. This is why regular maintenance is so important for your equipment.  

Heating and cooling units are mechanical equipment, which means they make noise. Not all that noise is bad, and even the occasional strange noise may merely indicate that it's time for a tune-up. However, any loud, disruptive or continual noises usually mean there's a real problem and you should contact a trusted local HVAC company like A.J. Perri to come and take a look. Trained technicians will be able to tighten and lubricate parts, replace belts and filters, and provide the solution to small problems before they become big repairs - or possible dangers.

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Last Updated: June 06, 2024