Furnaces aren’t 100% quiet pieces of machinery, and it’s not at all uncommon to hear strange furnace noises from time to time. But can you tell the difference between normal, harmless sounds and the kind of noisy furnace that might mean there’s trouble on the way? It’s important to learn about the most common heater noises and what they mean.
Why Are Furnaces So Noisy?
Furnaces are noisy, and there’s no getting away from it! They make little chirps, popping and crackling sounds, humming noises, and occasional thumps and bangs.
Like most mechanical systems, it’s completely normal for a furnace to be noisy sometimes. If your furnace makes small sounds once in a while, there’s usually no cause for alarm.
However, not all furnace noises are harmless. Sometimes your noisy furnace might be trying to tell you something. To make sure you know the difference between harmless furnace noises and noises that could mean trouble, it’s time to learn the language of furnaces!
7 Furnace Noises and What to Do About Them
1. Scraping and Screeching
If you hear scraping and screening noises coming from your heater when you turn it on, a likely culprit is the blower motor. This component is what forces warmed air through HVAC ducts. The motor needs to be kept well-lubricated so it can operate smoothly and quietly.
Potential noise-causing problems include:
- Insufficient lubrication
- Loose blower wheel
- Worn ball bearings
If you hear scraping noises coming from your furnace, there are a couple issues that might be the cause. Most of the time, scraping noises are due to either a loose blower wheel on the blower motor or worn ball bearings.
The fix: Check the blower motor and apply more lubrication if it’s looking dry: Two to three drops of lubricant per port is enough. For all other blower motor issues, call an HVAC technician for help.
Note: Because moving parts are involved, turn the HVAC off while waiting for a tech to come take a look.
2. Squealing and Shrieking
Does your furnace sound like it’s being murdered? High-pitched shrieking or squealing sounds can indicate there’s something wrong with the motor belt. It may be loose, or it could be worn, overworked, and about to give out entirely. In the latter case, you may also notice a burning smell coming from the motor belt.
The fix: This is a relatively simple and inexpensive problem to fix, provided it’s done sooner rather than later. An HVAC professional can get this done quickly, with the right tools.
Note: If there’s a burning smell coming from the motor belt, turn off the system and have an HVAC tech come out right away.
When an HVAC heating cycle begins, the blower motor in the furnace blows warm air through the duct network. Sometimes, when the cycle starts, you might hear popping noises.
Most popping noises are normal and nothing to worry about. They happen when warm air from the furnace mingles with cooler air in the ducts. The warm air causes the metal air ducts to expand slightly, sometimes causing a popping noise.
Less often, loud pops may be a sign that the gas burners in your heater are dirty. Sediment and debris collect on the burners over time. If they’re not cleaned regularly, the furnace’s heat exchanger may be damaged.
The fix: Schedule twice-annual professional HVAC maintenance, including AC, heat pump, and furnace. This will ensure your gas burners never get dirty enough to cause damage.
4. Rattling and Rumbling
Rattling and rumbling sounds typically mean something has come loose inside the furnace. If this happens, the loose part may be moving around inside the furnace and could potentially hit and break other components.
The fix: This should be addressed promptly to prevent further damage. Because it involves damage detection and may mean checking or working on a number of parts, this issue needs a professional. Call an HVAC technician for immediate help, and turn the furnace off in the meantime.
If you hear strange whistling noises coming from your heater, it typically means there’s reduced airflow somewhere in the furnace system. Most often, it’s due to a clogged air filter.
The fix: This one’s a DIY noisy furnace fix. Clean or change out dirty filters, and see if the whistling is gone. If you still hear the noise, check vents for blockages. Need help? Don’t hesitate to call CW Service Pros any time.
Most furnaces emit a low hum while they’re running through a heating cycle. However, if this normal low hum starts to get noticeably louder, then your furnace may be in trouble. A loud furnace hum typically indicates problems with either the capacitor or the blower fan.
The fix: These are potentially serious issues that may damage your furnace fan or motor. If your furnace is humming louder than it usually does, call an HVAC technician.
If your furnace is making loud banging noises or booming, it may be due to an ignition delay. This is typically because of a clog in the gas line or a problem with gas pressure. These issues cause gas buildup in the combustion chamber, leading to a small, contained gas explosion when ignition happens.
The fix: Gas issues need immediate attention, but do not attempt any kind of repair work yourself! Any and all issues with furnace burners should be dealt with by a licensed technician. This is particularly crucial if your furnace runs partially or fully on gas because disassembling or reassembling heater parts incorrectly may lead to a gas leak. Don’t sleep on this furnace issue—turn off the furnace and call a professional right away.
Silence Isn’t Always Golden: Carbon Monoxide Leaks
Many furnace noises—especially noises that show up suddenly or get louder over time—are signs that something is wrong. Unfortunately, some furnace problems aren’t noisy at all, making them difficult to detect and fix.
One of the most hazardous furnace issues, carbon monoxide leakage, is almost completely silent. It makes almost no noise at all. The most you might hear is a very faint whistling sound at the site of the leak.
In the event of a carbon monoxide leak, what you’re much more likely to notice is the smell. A carbon monoxide leak smells like rotten eggs, a very distinctive and strong-smelling odor.
In heaters, a cracked heat exchange can cause a carbon monoxide gas leak. Inhalation of this gas can cause dizziness, nausea, fainting, and other symptoms. If you ever notice this smell in your home, immediately evacuate the entire home and call emergency services.
PRO TIP: Banish Strange Heater Noises Forever (Well, Almost)
When a furnace makes strange noises, it’s almost always due to a preventable problem. Whether it’s a sediment-covered burner, loose or worn parts, or insufficient lubrication, regular professional maintenance can stop these problems from ever happening.
That’s why the best way to fix a noisy heater is by scheduling twice-annual maintenance with an HVAC professional. You’ll won’t have to worry about worn, loose, dry, or dirty parts again. Your HVAC tech will find and fix them before they become problems. You’ll have fewer issues with strange furnace noises, and your whole HVAC system will run more efficiently, keeping your home more comfortable through the winter.
What’s Your Noisy Furnace Trying to Tell You?
Many furnace noises are harmless, but sometimes a noisy heater is a sign of potential trouble. If your furnace is making warning noises that suggest trouble is imminent, don’t leave it to chance. For help with furnace maintenance and heating repair, call CW Service Pros today!
We’ll send an HVAC technician out to your home ASAP, with a same-day appointment, if possible, to have your heater repaired. And if a heating system replacement is necessary, we’ll let you know. Call CW Service pros to schedule an appointment.