Furnace ductwork oil canning noise in Greater Vancouver

That sudden bang or pop from the ducts when the furnace turns on or off is called oil canning, named after the way a metal oil can pops when you press it. It is common in older Greater Vancouver homes with sheet-metal ductwork, and while it is rarely dangerous, it is annoying and fixable. Here is what causes it.

What oil canning is and why it happens

Oil canning is the flexing of a flat sheet-metal duct panel as pressure inside the ductwork changes. When the blower starts, pressure suddenly rises and pushes a duct wall outward with a pop. When it stops, the panel snaps back. Large, flat, unsupported sections of duct are the usual culprits, and thinner gauge metal flexes more easily.

Several things make it worse. A restricted filter or closed registers raise the pressure swing, so the panels flap harder. Loose duct connections and long unsupported runs, common in older homes that have been renovated over the years, also amplify the bang.

• Large flat duct panels flexing as blower pressure changes
• Thin-gauge ductwork with little reinforcement
• A clogged filter or closed registers increasing the pressure swing
• Long, unsupported duct runs that vibrate and pop
• Loose duct joints that move when the system cycles

What you can do and the lasting fixes

First, reduce the pressure swing. Replace a dirty filter and open all your registers, which often softens or eliminates the bang on its own. These are the safe, no-cost steps any homeowner can take.

If the noise remains, the lasting fixes happen at the ductwork. A technician can add cross-breaking or reinforcing to flat panels, secure loose connections, or adjust the system so pressure rises more gradually. These are straightforward improvements that quiet the home without major work.

• Replace the furnace filter to ease the pressure change
• Open all supply registers rather than closing rooms off
• Have a technician reinforce large flat duct panels
• Have loose duct joints secured and runs better supported

Frequently Asked Questions

Is duct oil canning dangerous?

It is almost always a harmless noise rather than a safety problem. It does signal that pressure in the ducts is swinging more than ideal, so addressing it can improve both quiet and efficiency, but it is not an emergency.

Why does the bang happen only when the furnace shuts off?

When the blower stops, duct pressure drops fast and a flexed panel snaps back to shape, producing the pop. The startup and shutdown pressure changes are when oil canning is loudest.

Can changing my filter really stop the banging?

Often it helps a lot. A clogged filter increases the pressure difference across the ducts, so a clean filter and open registers reduce the swing that makes the panels pop. If it persists, the ducts may need reinforcing.

HeatLand Heating & Cooling is a licensed and insured, TSBC-certified HVAC company serving homeowners across Greater Vancouver. Our technicians diagnose the real fault, explain your options in plain language, and complete the work safely and to code.

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