11 Common Reasons for a Loud Furnace

hvac repair tech fixing loud furnace

Hearing noises from your furnace can be unsettling, more so from a relatively new appliance. Determining the source of the sound before addressing the issue is vital for long-term solutions.

Homeowners can find it hard to differentiate between a problem that requires immediate attention from a minor one. Regardless, you should never ignore a loud furnace because it indicates something is amiss with the unit’s internal working. By addressing such issues with professional inspection and repairs, you also reduce the chances of permanent damage.

Here are some of the noises you shouldn’t ignore:

  • Loud humming
  • Loud scraping
  • Screeching
  • Whistling
  • Banging
  • Rumbling
  • Rattling

Do not attempt to fix any of these noises without a licensed professional. The Lee Thompson Co. has knowledgeable technicians who conduct in-depth assessments and provide long-lasting solutions to promote your comfort. Here are some of the causes of loud noises you should look out for.

1. Clogged Filter

Clogged filters cause a whistling noise and reduce the airflow in your furnace, making the system struggle. This causes the blower motor to work harder than usual, which leads to louder noises. Homeowners can test this possibility by pulling the filter out and assessing whether the whistling stops.

If you are using disposable filters, you can address the issue by replacing an existing filter with a new one. However, it is appropriate to contact the professionals if there is a need for repairs. Remember to clean or change your filter at least once in three months for 1-to-2-inch filters. 3-to-4-inch filters can be replaced every 6 to 9 months. Also, check your filter every 30 days to identify forming clogs.

2. Dirty Burners

A layer of dust, dirt, and debris can create a humming sound when you turn your furnace on. This often occurs after a period of inactivity and causes delayed ignition. Homeowners should leave cleaning burners to the professionals. The reason being cleaning the burner incorrectly can leave a homeowner with a gas leak, which is a serious hazard.

3. Duct Issues

Ductwork can flex due to pressure changes between supply and return ducts, potentially causing banging and rattling noises. Alternatively, the noise could indicate that your HVAC ducts need reinforcement; either there are weak spots in the ducts or screws in the ductwork are loose, causing unexpected noises as air passes through.

4. A Dirty Pilot Light

Like dirty burners, dirty pilot lights can affect your ignition. A delay in the ignition can cause fuel build-up, and when it finally lights, it can produce a loud noise. Additionally, dirt build-up in the pilot light can make the light struggle to stay lit. Cleaning a dirty pilot light can be done using a can of clean compressed air to blow air through the pilot light. However, licensed technicians may opt to take the pilot light assembly apart to conduct in-depth cleaning.

5. Cracked Heat Exchanger

A cracked heat exchanger can cause whistling, scraping, and loud humming of the furnace. Failure to change the filter and clean your furnace regularly can restrict airflow, causing heat build-up that may eventually crack your exchanger.

A cracked heat exchanger is an immediate red flag because it can cause carbon monoxide to leak from your unit, potentially endangering the lives of home occupants. A carbon monoxide alarm should warn you of any leakage, and if it goes off, turn off the furnace, vacate everyone from the house, and call us immediately for assessment and repairs.

6. A Loose Blower Wheel

The wheel helps circulate air throughout the home. When it becomes unbalanced, it causes clanking or banging sounds as it moves rapidly and bumps against the shell of the blower. At worst, the blower fan could be broken and need replacement. At best, the wheel could be slightly damaged. If you hear this noise, shut off the furnace immediately and contact the experts to inspect the furnace. Using your furnace despite having a loose blower wheel could result in a more costly fix that could have been avoided.

7. Loose Screw or Parts

Rattling or banging noises within the appliance often suggest that its internal parts are loose or damaged. This can result in decreased performance levels, causing overheating and electrical problems if not addressed promptly. Additionally, your system could have worn-out parts that need replacing. Old blower fans, bearings, or belts may produce a grinding sound when the furnace turns on or off.

8. Unbalanced Air-to-Fuel Ratio

The furnace requires the correct air-to-fuel ratio to function properly. It heats the air as prescribed and ignites burners without delay. An imbalance can cause delayed ignition and a loud boom when the fuel finally builds up to the required level. Homeowners should not attempt adjusting the air-to-fuel ratio because it can cause excess gas usage and high energy bills.

9. A Failing Motor

The blower motor helps transport warm air via the air vents. If the blower belt starts weakening, it can cause the furnace blower to produce a squeal or a squeaking sound. Replacing the belt can stop the noise, but we do not advise homeowners against taking on the task themselves. We recommend switching off your furnace immediately and contacting us.

10. A Loose Vent Cover

Vent covers may be in the ceilings, on the walls, or on the floors. A loose vent cover could cause a rattling sound when wind blows through it. It can also settle on the floor with a loud noise when air suddenly stops flowing through the loose vent cover.

Fixing the issue involves tightening the screws holding the cover in place. We do not overtighten but ensure the screws are tight enough to prevent the rattling from recurring. We also propose checking the rest of the air vents in the house one by one to ensure all screws are tight as needed.

11. Ignition Roll-Out

This is a burst of flame bigger than it should be or a small explosion when the furnace turns on. It is uncommon but can be alarming. You can watch the furnace start up to check if the banging results from a gas ignition problem.

The first option is to look into the furnace doors to see what is happening. Alternatively, you can listen to pinpoint the exact source of the furnace. Another effective strategy is checking whether the furnace doors are shaking. Also, observe what happens if banging occurs. If shaking accompanies the noise or if you see an extra flame, you have identified a potentially dangerous issue and should correct it.

Let the professionals deal with the gas portion of your furnace. Also, note that newer furnaces have a roll-out sensor that shuts down the unit should the issue ever occur.

Dealing With a Loud Furnace

Loud furnace noises require immediate assessment. If you live in Houston, you can count on licensed and experienced technicians from The Lee Thompson Co. to help you diagnose and repair the issue on time for optimal performance levels. Additionally, we provide regular professional maintenance to help homeowners identify minor issues before they escalate into major concerns. This proactive approach will extend the life of your furnace, so you don’t have to deal with unexpected breakdowns or noise-related problems.

We are proud to offer a full range of repair, maintenance,and installation services for your heating and cooling systems. We also work with indoor air quality and HVAC zoning. Contact The Lee Thompson Co. today to schedule an appointment.