Low Humming Noise In Furnace [Even When Off] – What To Do?

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Appliances make noises when they operate, ranging from natural sounds to indications of a problem. When there's a low humming noise in your furnace, even when it's off, it's time to see what's wrong. For this post, we researched the causes of humming in a furnace and what you should do.

When your furnace makes a low humming noise even while it's not operating, it implies you have faulty parts that need replacing. The sound is usually a result of these damages:

  • Damaged Furnace Blower
  • Broken Capacitor
  • Malfunctioning Transformer
  • Loose Ductwork
  • Dirt Clogging
  • Faulty Wiring

If your furnace continues humming even when it's not running, it may mean a different issue. Keep reading to learn solutions for these complications and preventive measures to keep them from happening again.

Technician Looking Over A Gas Furnace, Low Humming Noise In Furnace [Even When Off] - What To Do?

Furnace Humming Noises - What Do They Mean?

Furnaces typically produce noises when they run, but if you notice the sounds getting louder, it's a sign of a problem. These problems mainly involve issues with parts that you can fix with a few adjustments or replacements.

Here are a few issues that cause humming in a furnace.

Damaged Furnace Blower

Furnace repair, maintenance, and troubleshooting.

The most common reason is a damaged furnace blower, which is responsible for distributing warm air from the ductwork to the rest of your home. Humming noises indicate that your blower failed or is close to breaking.

Compared to other complications, a faulty blower makes a more persistent humming. The noise could also come from other issues with the blower, such as low amperage or disconnected connections.

If you aren't sure what's wrong with your blower, contact a professional to evaluate it.

Broken Capacitor

A capacitor helps start and run the furnace, so if it breaks, the whole furnace is at risk of failing altogether. It produces a humming sound because it can slow down or completely stop the motor from turning.

If you encounter low airflow accompanied by humming sounds, it means the capacitor failed. In this case, you need to replace the motor and capacitor for your furnace to run smoothly again.

Malfunctioning Transformer

When electricity passes through a transformer, it could cause the device to vibrate and result in a low humming sound. If this is the case, you don't have to worry!

Louder noises may be due to failure or poor installation. If there's a problem with bolt security, you can fix it yourself, but a professional should do the repositioning and replacement.

Note that if your transformer produces a loud humming noise and you own an older furnace model, you likely need to replace it.

Loose Ductwork

Inspect your ventilation if there doesn't seem to be any loud humming from your furnace or nearby. The noise may come from loose ductwork connections instead of the HVAC itself.

Air comes through the ducts of the HVAC system with pressure, so, over time, the screws that put the ductwork in place dislodge as it wears.

You can also look around for other loose screws in the furnace or close to it that could produce the sound.

Dirt Clogging

Most experts recommend servicing your furnace at least once a year to keep it working in top condition. Letting it go without professional maintenance can result in dirt and debris buildup.

Dirty gas burners are a common cause of humming noises. Although it usually only requires a good cleaning, it may lead to further problems with the furnace's gas supply, ignition, and performance when left for too long.

Faulty Wiring

HVAC Installer Strips Small Wires for a new Residential Furnace

Issues with electricity flow and wiring within the device also produce humming or buzzing sounds, mainly because it connects to the rest of the furnace's parts like the blower, thermostat, and more.

Loose wires make a consistent humming while the furnace runs, but if it involves faulty wiring wherein two bare wires touch, it could lead to a severe fire hazard.

If you suspect loud humming sounds or any unusual noise from your furnace, it's best to contact a professional as soon as possible to prevent serious harm to you and your home.

Why Is My Furnace Humming When It's Off?

For a natural gas furnace, the primary reason it hums when off is due to the wrong adjustments on the blower's pilot light. To fix it, you should readjust it to the proper level.

Gas releases when you turn on your furnace to heat your home, then the pilot light ignites the gas and pumps it into the main burner. If the pilot light is faulty, your furnace will not produce heat since its burners won't ignite.

You will need to relight the pilot light by locating the reset switch and manually lighting it up.

With newer electricity-powered furnaces, humming noises while off can come from problems or loose connections with the transformer or ductwork.

Can I Stop My Furnace From Humming?

Depending on the problem, you can stop a furnace from humming. You can work on some issues yourself, but a professional should handle anything significant.

Here are a few ways to eliminate humming noises from your furnace or around it.

Replace Parts

The quickest solution to issues with your furnace parts is replacing them, but it also costs the most. If the furnace parts are completely damaged, you may not have another choice but to get a replacement.

Tighten Screws

Humming sounds may come from loose bolts or connections with furnace components or ductwork. When this is the issue, you only need to screw back dislodged bolts tightly.

Thorough Maintenance

Maintenance may be the solution if you know you haven't had your furnace serviced for a while. Thorough cleaning and lubrication may eliminate the humming without requiring repairs or replacements.

Proper maintenance also extends the life of your furnace, so you wouldn't have to resort to replacements unless the damage is severe. Below are a basic maintenance practices for a furnace:

Inspect Filters

Male hands are installing a furnace air filter. This filter is not brand new but it is relatively clean, it was removed for inspection.

A furnace filter eliminates dust, bacteria, mites, spores, and other particles from spreading to indoor air. If your filter is dirty, it results in low airflow and less efficiency.

If your filters seem dirty or clogged, you can either clean them or replace them with fresh ones. Most furnace filters can last a while, but it usually depends on the size.

Check out the Filtrete AC And Furnace Air Filter on Amazon.

Evaluate Blower Motor

For your furnace to function as needed, you should ensure your blower operates correctly. It has many parts, so maintaining it is crucial to keep it from breaking.

As much as possible, repair issues with the blower motor the moment you notice any to prevent further complications.

Reduce Heating Load

Identifying the sources of heat loss around your home can help reduce your HVAC system's heat load, keeping temperature conditions comfortable and increasing efficiency.

Common remedies include weather stripping windows and doors, sealing leaks and gaps, and insulating ductwork and foundation.

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Check Ventilation And Ductwork

It's essential to have proper air circulation for your heating system to work effectively. Next to a fully functional furnace, your vents should be clear and free of blockage from furniture, objects, or even dirt.

Regularly check on your vents and ductwork and clean them as much as necessary. Shut off your HVAC and its primary power source, remove floor registers and covers, then vacuum any dirt or scraps within the vents.

You can also clean them using soapy water or cleaning solutions and a clean cloth.

Professional Repair

If DIY remedies don't seem to work, it's time to consider having your furnace repaired by an HVAC professional. Usually, they would have the right equipment to fix most problems with your heating system.

How Much To Repair A Furnace?

Heating Central Gas Furnace

Furnace repairs can range from $85 to $2,050, depending on what needs fixing or the type of furnace you own. Some technicians will charge an hourly rate or extra fees for additional work, such as setting up and cleaning.

Be sure to ask your HVAC technician for pricing details to get an accurate estimated price or directly request a quote for your issue.

How Long Does A Furnace Last?

The average furnace can last from 15 to 20 years with adequate maintenance. If you're diligent with repairs and frequently service the furnace, you can extend its life a few more years.

Once your furnace reaches the 15-year mark, evaluate its condition to see if you need to make replacements or if you should upgrade it to a newer model.

In Closing

Independent heating in a modern house

Low humming noises coming from your furnace are natural during operation unless they become significantly louder.

In this case, you may want to inspect your furnace parts or ductwork for any damages, loose components, or maintenance-related concerns.

If your furnace makes a low humming noise even while it's not operating, it could have faulty parts that need replacing.

Read these posts for solutions to other unusual noises coming from your furnace:

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