Why Is My Furnace Making Noises? Troubleshooting Common Issues

While it’s normal for a furnace to make low sounds as it operates, louder rattling, whistling, and screeching noises can be cause for concern. If you hear any of these noises, check to make sure the thermostat is set to heat and that your air vents are open.

A squealing sound may indicate that the blower motor needs lubrication. You can try adding some lubricant yourself, or you can call in a professional.

1. Loose Parts

Rumbling and rattling sounds are usually caused by loose screws, panels or other parts that vibrate as your furnace runs. The sound can also be the result of dirty air filters or ducts that restrict airflow. If the sounds are high-pitched, they could indicate that your heat exchanger is cracking or breaking apart.

Clicking noises usually happen once per heating cycle and indicate that your furnace is starting a new cycling phase. However, if you hear these clicking sounds more frequently than normal, it might mean there’s an electrical problem with your system.

A rattling sound can indicate that there are loose bolts or panels in your furnace’s access hatch. These rattling noises aren’t typically a big deal, but they should be addressed soon to prevent them from becoming worse. A rattling sound may also indicate that the blower motor fan belt is wearing out and needs to be lubricated. A professional can adjust the blower fan belt or replace it if necessary.

2. Dirty Filter

While every mechanical device produces some noise, the sounds of your furnace should be relatively quiet and unobtrusive. Unusual sounds like rattling or whistling are usually a sign of a problem that will require the help of a professional. Observe when these sounds occur–during startup or operation–to determine the source of the issue.

A rattling sound typically indicates a loose panel or screw. If the rattling is heard throughout the entire heating cycle, this may indicate that the blower motor needs re-tensioning or replacing. This is an easy repair for a certified technician!

A whistling sound from your vents or ducts is caused by a dirty filter. This reduces airflow and forces the furnace to work harder, creating a whistling noise. Be sure to change your filter regularly for best results.

3. Dirty Burners

Most mechanical devices make some noise as they work, and furnaces are no exception. When unusual sounds are coming from your furnace, they probably indicate that something needs to be fixed.

If you hear a scraping sound, that could be metal rubbing against another part of your furnace. Before you enter your furnace, turn off the power and gas by turning the electrical disconnect switch to the “off” position.

Then, shut off the gas valve. Next, open your vents. If you hear a scraping sound, it could be an indication that the blower wheel has become dirty and needs cleaning.

A whistling sound is often the result of a dirty air filter or an obstructed vent. Replace the filter or remove it completely, and check your vents for obstructions. If the problem persists, it might be time to call a technician for a professional inspection and cleaning. It will save you money in the long run by reducing your utility bills and keeping your heating system in good condition.

4. Delayed Gas Ignition

When your furnace kicks on and makes a banging or boom sound, it is an indication that the gas cannot ignite. This is a dangerous problem and should be checked out by a technician as soon as possible. The booming noise may also be caused by expanding or retracting metal air ducts, which is a common issue that is usually easy to fix.

When your thermostat calls for heat, a gas valve opens and the burners deliver the fuel that is then ignited in the combustion chamber. When the ignition system is faulty, this process can’t happen, and the gas continues to build up until it finally ignites, resulting in a small explosion that can damage your furnace and create a carbon monoxide poisoning hazard for your family. A quick call to your heating and cooling company can help solve this dangerous problem. They can inspect your furnace for issues like a dirty gas burner that prevents it from igniting, which is often the cause of delayed ignition.