Why would this chimney have a crack straight up the middle?

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Does this flue serve a wood burning appliance?

If so and the chinney was not built using the best practices, could be caused by a chimney fire expanding the clay tiles which pushed against the block creating the crack.

The expansive forces of nature by heat expansion or when water freezes are very powerful!

What were the soils or visible support under the chimney? Their condition? Any signs of rotation away from structure…?

You’re in a place that freezes very nicely too, I think.

Just a guess without a pic of the top of the chimney. Moisture infiltration at the chimney cap and no rain cap have caused the rebar in the block to rust and swell causing a crack which allows more moisture and so on. My disclaimer on this is that we only have three chimneys here.


It appears to be an expansion crack due to excessive heat. I would expect any water that entered would wind up at the bottom before it froze. Excessive heat would expand the entire chimney causing the expansion crack to go all the way up.

It does have a wood stove.

No signs of rotation and it sits on a strong footing.

I recommended them to call a chimney sweep. thank you, every one.

Brian nailed it…improperly built chimney. GC warranted.