Furnace Making Loud Noise / Banging

Common Symptoms

You might be experiencing this problem if you notice any of these signs:

• Loud boom or bang when furnace starts
• Continuous rumbling or roaring sound
• High-pitched screeching or squealing
• Rattling or vibrating noises
• Whistling or hissing sounds
• Clicking sounds that don't stop
• Grinding or scraping metal sounds
• Loud popping from ductwork
• Thumping when furnace shuts off

Step-by-Step Diagnosis

Follow these steps to identify the exact cause of your problem:

1. Identify when noise occurs (startup, running, shutdown)
2. Determine noise type (bang, screech, rattle, etc.)
3. Check if noise comes from furnace or ductwork
4. Inspect air filter for severe clogging
5. Listen to blower motor operation
6. Check for loose panels or access doors
7. Verify all duct connections are secure
8. Note if noise started suddenly or gradually
9. Check flame color during ignition (should be blue)
10. Feel for excessive vibration
11. Test if noise changes with thermostat fan setting
12. Record video of noise to show technician if needed

Most Common Causes (Ranked by Likelihood)

DIY Solutions

Step-by-Step Instructions:

1. Replace air filter if dirty or clogged
2. Tighten all visible screws on furnace panels
3. Check and secure loose ductwork connections
4. Inspect blower motor access panel - ensure it's properly seated
5. For banging at startup, shut down and call professional immediately
6. Apply duct tape to loose or vibrating duct seams
7. Check for objects that fell into ductwork through vents
8. Lubricate blower motor if it has oil ports (older models)
9. Secure any loose wiring with zip ties
10. Add dampers to ducts that expand/contract loudly
11. Ensure furnace is level and not rocking
12. For screeching, shut off immediately - likely motor bearing failure
13. Document noise pattern and when it occurs
14. Call professional for any noise that indicates combustion problem

When to Call a Professional

Don't attempt DIY repairs if you experience any of these situations:

• Loud boom or bang when burners ignite
• Screeching or grinding sounds from blower
• Rumbling that continues after burners shut off
• Any smell of gas accompanying noises
• Visible cracks in heat exchanger
• Furnace age over 15 years with new noises
• Noise started suddenly and is getting worse
• Blower motor won't run or runs intermittently
• Metal-on-metal grinding or scraping
• Carbon monoxide detector alarming

Prevention Tips

Stop this problem before it starts with these preventive measures:

• Schedule annual furnace cleaning and inspection
• Replace air filters monthly during heating season
• Have burners cleaned every 2-3 years
• Lubricate blower motor bearings annually (if applicable)
• Keep furnace area free of storage and debris
• Install whole-home humidifier to reduce duct expansion noises
• Tighten furnace panels and ductwork annually
• Address small noises early before they worsen
• Install rubber isolators under furnace to reduce vibration
• Consider upgrading 15+ year old furnace before major failure