Why is my furnace making noise?

The nostalgic hum of a furnace can be a comforting sound in winter—for some of us, it’s the equivalent of a lullaby. Which is why it’s so jarring when a furnace suddenly starts making loud and unusual noises.

Table of contents:

• Are weird furnace sounds dangerous?
• How to troubleshoot why your furnace is making noise
• Why is your furnace acting up?
• How to lengthen your furnace’s lifespan
• Should you replace your furnace?
• The best furnace replacement
• How to get a system installed by experts 

And unusual noises aren’t just irritating; they’re legitimately a cause for concern, indicating underlying issues with your furnace—issues which could actually be dangerous. 

Not great, to say the least. But what to do?

At Sealed, we’ve seen a cranky furnace or two (or a thousand!). So in this article, we’ll share everything we know about why your furnace might be making a racket and how to troubleshoot—fast. Then, you’ll learn what you can do to resolve the problem and get some peace (and peace of mind!) again.

Sound good? Let’s dive in.

Is a buzzing furnace dangerous? Here’s when furnace sounds are a safety risk

Before we delve into the specifics of furnace noises, let’s talk about safety. 

In some instances, furnace noises can indicate immediate danger to you and anyone else in your household.

If your furnace is powered by natural gas, any irregular noises (like a furnace making a buzzing noise) should be taken extremely seriously—they could be a sign of gas leaks. 

Gas leaks can pose significant health risks, including carbon monoxide exposure—the “silent killer.”

(Read Is your home’s air quality healthy and clean? to learn more about what affects indoor air quality.)

Gas leaks can pose significant health risks, including carbon monoxide exposure—the “silent killer.”

But not every killer associated with gas furnaces is silent! 

If you hear a loud bang or thud when turning on your furnace, this could mean the buildup of gas in the system has become too great. This is a potentially catastrophic condition and requires immediate attention from an HVAC professional.

Basically, if you ever notice a significant difference in how your gas furnace sounds, turn off your furnace immediately, leave your home, and contact your gas company and a professional HVAC technician. Better safe than sorry (1).

By the way, gas furnaces come with plenty of other health risks if not properly maintained or ventilated. 

Here, you can read about the safety of gas appliances and if you need actually gas in your home. (And after you do that, consider this a sign from the ether that it’s time to check the batteries in your carbon monoxide detector.)

If your electric furnace starts emitting a persistent buzz or “sizzle,” this could signal the malfunction of components like relays or transformers, and that could cause an electrical fire. 

If you notice an unusual buzzing sound coming from in or around your electric furnace, shut it off right away, unplug it from the wall (if possible), and contact an HVAC technician as soon as possible.

We’ll throw in here that you really don’t want to hear “sizzling” from any of your appliances or wiring—anywhere in the house. If you do, call an electrician immediately. That’s not a good sign and could be a precursor to a house fire (2).

(Related read: Why does my furnace smell like it’s burning?)

How to know if a furnace needs maintenance: Troubleshoot why your furnace is making noise

Now we come to the heart of the problem.

Let’s take a close look at what noises your furnace could be making—and what those noises could mean.

1. Clicking, clanking, and scraping
2. Rattling
3. Screeching or squealing
4. Booming or knocking
5. Clicking
6. Buzzing or humming
7. Thumping or vibration
8. Hissing

Clinking, clanking, and scraping

If it sounds like a mini blacksmith is working overtime in your furnace, it could be due to a loose or out-of-balance blower wheel. 

This metal component can start clinking against other parts when it’s not secure. If you’re the DIY type, you might try tightening it, but if the metallic concert continues, it’s time to call in a professional (3).

Rattling

A rattling noise can indicate loose or damaged components within your furnace. Loose screws, bolts, or even broken motor mounts could be the culprits. 

Carefully turn off your furnace and inspect it for any visible loose parts or screws. Can’t find anything? Call a tech. It could be something more serious.

Screeching or squealing

High-pitched squealing or screeching noises often point to issues with the bearings of the blower motor (or sometimes the fan belt). Over time, the blower fan and other parts can wear out or become misaligned, causing friction and noise. 

How serious is the squealing sound problem? It depends—it could be nothing more than a need to replace the bearings, or it could signal more extensive damage. In any case, it’s time for some furnace maintenance—you’ll need to call in an HVAC tech to take a look (4).

Booming or knocking

Hear a loud, sudden sound? These loud noises sound scary, and in the case of natural gas furnaces—they are. Very scary. 

If your natural gas furnace starts making a loud booming, knocking, or banging noise, turn it off and get out of there. It usually means there’s a delay in ignition due to dirty burners.

Natural gas heating is the largest in-home contributor to the 7.5 tons of CO2 equivalents produced by US households annually.

ccfpd.org

Clicking

This one can be tricky. A clicking noise during startup and shutdown is relatively common and might not be a cause for concern. 

However, if you start to hear a clicking that you haven’t heard before, it’s worth having a professional inspect your furnace—there could be something wrong with the ignition (5).

Buzzing or humming

A constant low buzzing or humming noise could indicate an electrical problem. This could be anything from a faulty capacitor, a problem with the fan motor, or an issue with the transformer. 

Electrical issues can be hazardous, so it’s recommended to turn off the furnace and contact a professional for a thorough inspection and furnace tune-up.

Thumping or vibration

Thumping, vibration, or a constant drone can be a sign that your furnace’s blower wheel is out of balance. This could be due to accumulated dust, dirt, or damage to the wheel itself. 

Cleaning the wheel or replacing it if damaged will typically solve this issue, but you need an HVAC tech to do it. Call ’em quick before the issue causes permanent damage (6)!

Hissing

Hissing could be a sign of an obstructed or dirty air filter—or it could signify a gas leak. If you ever hear hissing from your furnace, shut it off immediately. 

And if your furnace is powered by natural gas, it’s time to get out of the house and call your local gas company and HVAC technician for assistance (7).

We should be clear here, too—furnaces are complex pieces of machinery.

Just because you have a good idea of what might be going wrong with your older furnace doesn’t mean that it’s the best idea to attempt to fix yourself. 

There’s a reason we keep coming back to the Call a Technician! refrain.

Unless you know exactly what’s going wrong with your furnace and are 100% confident you know how to fix it safely, it’s always best to call in the professionals.

Why is your furnace acting up? 

A good question you might be asking here is, “Why is my furnace suddenly having problems?”

This question is especially pertinent if your furnace isn’t at the end of its expected lifespan. 

We expect older furnaces to act up, but a furnace that’s five or ten years old shouldn’t be having serious problems, right?

Kind of. The average life expectancy of a furnace is eighteen years, but the thing is: A lot of factors can affect the lifespan of a furnace, such as:

• How often and how well the furnace is maintained
• The kind of furnace it is (oil, natural gas, or electric)
• How hard the furnace has to work to keep your house warm

That last one is the biggie. Many folks assume that the lifespan estimate for a furnace is a concrete expectation of how long the furnace will last. 

But, really, it’s just an estimate of how long the furnace can last under ideal circumstances.

Furnace on its last leg? Discover if you could get a high-performance replacement with an energy-savings gaurantee.

And—we hate to break it to you—but unless your home was built recently and by contractors who had comfort and efficiency as top priority… there’s a good chance that your furnace is not operating in ideal circumstances.

85% of single family homes were built before the year 2000, when residential energy standards became prevalent in building codes. This means at least 8 out of 10 American homes are inefficient.

statista.com

What do we mean?

Well, lots of American homes:

• Have tons of gaps and air holes throughout the home, which means plenty of cold air coming in from the outside (8)
• Are under-insulated—especially at the top of the house—which allows lots of heat to escape through the roof
• Don’t have adequate air circulation, leading to hot and cold spots in the home

For a quick visual on how to keep the outside air outside, watch this video:

All of these factors can put unnecessary strain on your furnace. 

And if your furnace is having to work extra hard to keep up with temperature swings, then it’s more likely to start acting up much sooner than expected.

How do you prevent this situation?

Lengthen your furnace’s lifespan (and avoid mysterious furnace noises)

The best way to ensure your furnace lasts as long as possible is two-fold:

1. Keep it properly maintained
2. Ensure your house is properly insulated (especially around your attic) and air sealed.

If you haven’t heard of air sealing, just know it’s the process by which contractors find and seal up all the gaps and holes throughout your home that are allowing air to escape. Here, you can read all about air sealing in our complete guide.

When your house is properly air sealed and insulated, it’ll allow your furnace to work much less to keep up with your home’s heating needs. That means your furnace will be more efficient, last longer, need fewer repairs… and will have you feeling comfortable all year round.

Sealed exceeded our expectations in every way… They sealed our home with insulation and our house is warm! It was wonderful to put away our space heaters…. We definitely recommend this company!

Annaliesa P., Sealed customer

Okay, as of now you may find yourself asking: “Should I just replace my furnace? If so, what kind of heating system should I replace my furnace with?”

That’s a bit of a complex question…

Should you replace your furnace? A 2-minute breakdown.

So is it time to move on from furnace repair and pay to replace your furnace with newer, more efficient (and quieter!) technology? Maybe. 

Here are some factors to consider.

You might be better off repairing your furnace if all of the below apply…

• If the furnace is young—less than 10 years old
• If it heats your home absolutely evenly
• If it’s burning fuel cleanly, with NO smells
• If it’s been well maintained throughout the years
• If the cost of repairs is less than 50% the cost of a replacement heating system—and the furnace is new enough that you don’t expect more repairs in the near future
• If you’re prepared to help the furnace out by air sealing your home and/or upgrading insulation

But you might be better off replacing your furnace if…

• The furnace is more than 10–15 years old
• You’re always repairing it
• It’s not keeping your home warm (that’s its whole job, after all)
• The furnace is too noisy and repairs don’t help
• Your energy use keeps climbing and you want something more efficient
• You’re concerned about carbon monoxide (or clean air is a priority)
• You live in a large, old house that’s tough to heat
• Your ductwork is in bad condition—causing bad airflow
• You want more energy-efficient heating (such as a heat pump)
• You’re uncomfortable with the age or condition of your furnace
• Or… you’re renovating your home anyway (why not do all the projects at once?)

(Related read: How long does a furnace last?)

The best replacement for a noisy furnace

Leaning toward upgrading your furnace?

That’s a good choice for a lot of folks—especially if you replace your furnace with better technology.

And if that’s your plan, the choice is clear: Go for a cold-climate heat pump.

(Related reads: How to go from gas to electric | How to go from oil to electric)

If you’re not familiar with heat pumps, basically they’re just like your air conditioner, only they work both ways: 

They can heat your home during the cold months and cool it during the hot ones. 

And they do both jobs really, really efficiently. In fact, a new cold-climate heat pump can be up to 3x as efficient as your old furnace. (Here’s why heat pumps are so efficient.)

Some other benefits of heat pumps:

1. Versatility: Heat pumps can both heat and cool your home, providing year-round comfort without the need for separate heating and cooling systems. No more maintaining multiple systems! Hurrah!
2. Safety: Heat pumps are completely safe appliances. They don’t emit weird gasses or chemicals and they run on non-combustible energy (which means there’s no risk of explosion—always a good thing!).
3. Longevity: Heat pumps are known for their durability and longevity. With proper maintenance and care, a heat pump can serve you well for 20+ years.
4. Rebates and financial incentives: If all that isn’t enough, consider the fact that—thanks to the 2022 Inflation Reduction Act—you could get up to $2,000 in tax credits for upgrading to an energy-efficient appliance like a heat pump. Here’s the lowdown on how to take advantage of heat pump rebates and tax credits.
5. Quiet: Last but absolutely not least, heat pumps are incredibly quiet. Most owners don’t notice when their heat pumps are running, no matter the time or circumstance.

(Learn more about heat pumps vs. furnaces here—or click here if you want to compare heat pumps vs. boilers.)

The bottom line? Heat pumps are the best replacement for a noisy furnace. So if you’re ready to retire the old clunker (literally) and upgrade to something more efficient and longer-lasting, look into installing a cold-climate heat pump in your home.

Especially since the whole process can be ridiculously easy: If your house qualifies, you can get a new heat pump (plus any other home efficiency upgrades you need) installed by experts.

And with Sealed, qualifying projects are backed by our energy-savings guarantee. That means they’re guaranteed to work.

Sealed has a fantastic business plan to assist homeowners to depart from oil and gas heating systems and [move] into the future of highly efficient HVAC electric systems. I highly recommend working with [Sealed].

Piper B., Sealed customer

Get a new system installed by experts

Cut energy costs and feel comfortable all winter with Sealed. (We guarantee your results for qualifying projects.)

Upgrading your HVAC system is complex and stressful, and making sure it’s done right the first time can be a headache.

That’s where Sealed comes in. With Sealed…

1. The whole upgrade process is hassle free. We make the whole-home comfort upgrade process hassle free—including a free energy assessment and flexible payment options.
2. We’ll do the heavy lifting and paperwork. We vet the best home performance contractors in your area, matching you with the right one based on their expertise and the unique needs of your house.
   
   And we meticulously research what upgrade rebates your project might be eligible for—and lead the way in helping you understand what’s available.
   
3. The upgrades will work. Your house will become a comfortable, energy-efficient marvel. (We stand by our work.) You get to sit back and enjoy hassle-free home upgrades that make your house feel better year round.

Fill out our quick questionnaire to see if your house qualifies to work with Sealed and our famous Sealed energy-savings guarantee.

Sit back and enjoy hassle-free home upgrades that make your house feel better year round.