Stoves That Go Bump in the Night

Q: We had a new wood stove installed last Fall, and are now using it daily. The problem is, we're occasionally startled by a muffled (but still loud) BANG coming from the stove. It seems to happen when the secondary flames are raging, which is when I assume the stove is at its hottest. This usually happens after we've gone to bed, and it sometimes wakes us up. Any idea what is causing this, and what we can do about it?

-Stan from Massachusetts

You don't mention it, but I'm betting your stove is made of plate steel, or has a sheet metal outer plenum or heat shield attached. When a panel of plate steel or sheet metal is welded or bolted to other panels so it can't expand as it heats up, pressure can build up until it "relieves" by flexing slightly in one direction or the other. This sudden action is often accompanied by a ticking, popping or banging sound. The old timers refer to the phenomenon as "oil-canning," because it mimics, on a larger scale, the action and sound produced when the bottom of an old fashioned metal oil can is depressed to dispense the oil.

If you can identify the plate that's oil-canning, you can sometimes solve the problem. If it is a sheet metal plate such as a rear heat shield or insert plenum, try inserting a non-combustible wedge between it and the adjacent wall of the stove, right in the center. The constant pressure in one direction will prevent the plate from oil-canning as it expands. I haven't tried this next one, but I've heard folks claim that striking the center of the offending plate with a hammer, denting it slightly inward, will create the same result.

If the "banger" is a heavy gage plate steel firebox component, the above tricks aren't going to work, but there's still good news. With time, the metal will usually "relax" into its range of expansion and contraction, and the oil-canning will stop on its own.

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