Is your heating or HVAC system making pops, bangs or booms? Are you hearing rattling, rumbling or clamoring from the walls or air vents? Before you get left in the cold this winter, use this guide to help you identify duct and furnace noise, and decide if you may troubleshoot the issue or if it’s better to call in an HVAC professional.
Locating the Noise
The HVAC system consists of the heating and cooling units, blower, air ducts, return grills, vents and the air filter. All of these components have the potential to make or cause unsettling noises when something’s wrong. However, since the HVAC system sprawls out of sight through much of the home, duct and furnace noise can be difficult to pinpoint. If the unusual noises aren’t simple to locate, you’ll need to investigate all accessible HVAC components to find the problem area.
The typical ductwork system is fabricated from sheet metal and connects to all living spaces of the home using many parts, dampers and sealants. Duct sheet metal may cause all sorts of noises from one or several different reasons.
Following are common duct noises, and what may be causing the problem.
- Rattling: Rattling noises are often the result of loose metal ducts knocking against each other. As ducts age, the sealing fails and duct connections wiggle loose from the static pressure.
- Popping and banging: Popping and banging sounds are caused by the movement of duct walls due to temperature changes.
- Booming: A loud booming sound is common at the connection of the duct trunk and plenum. This connection endures the greatest temperature swing, and there may be inadequate dampers or expansion joints to isolate the noise. The result will be a loud boom that echoes through supply ducts.
- Shaking or vibrating: When the return side airflow is blocked from a clogged filter, a substantial pressure drop occurs, which can cause the duct walls to shake, knock or vibrate.
- Scratching or buzzing: Mice, rats, raccoons, squirrels, bees and even large insects will make noise, such as scratching, buzzing and humming, if they find a way inside ductwork.
Home safety is important to keep in mind when dealing with a furnace. Dangerous carbon monoxide (CO) leaks may occur if components aren’t well maintained. If your furnace is making any of these noises, it needs attention.
- Rumbling: A rumbling noise from the furnace is indicative of a dirty or corroded heat exchanger.
- Huffing and puffing: If your furnace huffs and puffs, it may have a faulty or corroded gas valve or burner.
- Squealing: The blower and blower motor are responsible for many furnace or heat pump noises. A squealing noise may indicate a frayed belt, or the blower and housing may also need to be thoroughly cleaned and serviced.
- Grinding or scraping: Grinding and scraping noises tend to be more serious and indicate a failing blower motor. Either the blower motor is simply at the end of its life span, or neglect of proper maintenance have caused the motor parts to fail.
- Knocking: A correctly-installed vibration damper is necessary to prevent the blower compartment or air handler from making knocking noises or sending all sorts of other noises through the ductwork.
Troubleshooting Duct and Furnace Noise
Many duct issues may be performed by the homeowner. The first place to check, regardless of the noise, is the air filter. If it’s dirty, replace it. If it’s clogged, it may be the cause of some of the noises, as well as higher energy bills. If you heard rattling noises, you may be able to seal loose ductwork connections with metal-backed tape and an aerosol or paste sealant.
Depending on the severity of the issue causing duct and furnace noise, you may be able to handle the issue yourself, if desired, or some issues require professional solutions. First of all, if grinding or scraping noises are the issue, you should turn off the furnace and call your HVAC professional. However, all furnace problems are a serious matter since you’re dealing with fuel combustion and potential carbon monoxide. Whether a thorough cleaning or simple repair, it’s best to leave furnace issues to certified HVAC pros.
If you haven’t scheduled professional HVAC maintenance this season, the best advice is to call your trusted heating and cooling professional for preventive maintenance and diagnose any issues.
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