Heating Systems Create Odd Noises — What They Mean and When You Should Worry

furnaceDuct and furnace noises are common, and while some are perfectly harmless, others may be signs of serious problems that could pose safety risks, reduce system efficiency or cause expensive damage to your system. If the ducts or furnace in your Macon home are noisy, there are a few things you can do to try to quiet them, but some noises will require the attention of a qualified HVAC professional.

Quick Lesson in Furnace and Duct Anatomy

To understand duct and furnace noises, it’s important to know how your system works.

There are two types of ducts connected to the furnace. The return ducts connect on one end to the air return registers in your room, and bring cool air into the furnace through the main return duct, which is located next to the air filter slot. As cold air enters the furnace, it moves through the air filter, which removes dust from the air.

The filtered air moves over the heat exchanger inside the furnace, warming it. The warm air gathers in the plenum, the large metal box on top of the furnace, and the blower sends the warm air into the main trunk of the supply duct, which branches off into smaller ducts connected to the supply registers in your rooms.

Common Furnace Noises

While every furnace makes a little noise, these sounds shouldn’t be ignored, as they may indicate serious issues that can damage your system beyond repair if not addressed immediately by a qualified professional.

  • Loud booms, bangs or thuds coming from the furnace when it starts up is a likely indication of an ignition delay problem. Gas builds up on the burner before the pilot light finally ignites it, resulting in a little explosion that can seriously damage the heat exchanger. The ignition problem could be due to defective or dirty burners, pilot light issues or a misaligned burner assembly.
  • Rumbling noises inside the furnace could be due to a leak in the heat exchanger, which could result in the need for a new system.
  • Screeching or squealing sounds are often caused by a faulty blower motor, unlubricated bearings, or a loose or frayed belt.
  • Loud, metallic scraping noises are typically caused by a loose or broken blower wheel or a broken motor mount.

Common Duct Noises

Some duct and furnace noises are similar, and it may be difficult to tell whether the sound is originating in the furnace or the ducts. Try to follow the source of the sound and identify where it’s coming from. These are some of the more common noises you may hear coming from your ducts.

  • Booms, bangs or high-pitched whistling or whining noises in the ductwork typically occur when there’s an airflow issue, which may result from a dirty air filter, obstructed or closed registers, or undersized or poorly designed ducts. Try replacing the air filter and opening any closed registers. If that doesn’t solve the problem, an HVAC professional can measure the airflow and inspect the ducts to pinpoint the culprit.
  • Rattling or flapping sounds in the ducts typically indicate debris in the ductwork. Especially if return registers are built into the floor, small toys, nails and screws and other items can fall into the ducts and cause noise when air flows through. A thorough duct cleaning usually takes care of these sounds.
  • Popping or ticking sounds coming from the ductwork are common and typically associated with the expanding and contracting of the metal as warm air heats it up, and again as it cools down once the system cycles off. Sometimes these noises are due to the expansion and contraction of the hardware that holds the ducts in place. You can slide small pieces of foam or rubber between the duct and the brackets to help quiet down or eliminate these noises. Insulating the ducts can also help control the frequency and volume of these sounds.

Preventing Duct and Furnace Noises

Annual preventive maintenance on the furnace each fall will help prevent duct and furnace sounds due to airflow problems and loose, broken or dirty components. The technician will measure the airflow, lubricate moving parts, as well as inspect belts, connections,and essential components. He will also clean and inspect the burner assembly, among other essential tasks. A yearly tune-up extends the life of your equipment and helps improve energy efficiency.

For more expert tips on diagnosing and preventing duct and furnace noises, please feel free to contact us in the Macon area at Wilson Bryant Air Conditioning.