Do chimneys expand vertically?

  • Active since 1995, is THE place on the internet for free information and advice about wood stoves, pellet stoves and other energy saving equipment.

    We strive to provide opinions, articles, discussions and history related to Hearth Products and in a more general sense, energy issues.

    We promote the EFFICIENT, RESPONSIBLE, CLEAN and SAFE use of all fuels, whether renewable or fossil.


New Member
Mar 28, 2023
When I was resealing the storm collar on my steel chimney recently, I noticed that it was held to the roof flashing with 2 screws. I was wondering, do chimneys expand vertically when they heat up? If so, should the storm collar be able to move upward w the chimney? Maybe those 2 screws shouldn’t be there. Thanks for your input.


Staff member
Nov 18, 2005
South Puget Sound, WA
Normally the storm collar is not screwed. It is held in place with a bead of good-quality silicone.
  • Like
Reactions: cahaak and Bryce250


Minister of Fire
Jan 12, 2009
SW Virginia
Steel expands in all directions when heated but you'd notice it the most along the longest dimension.
It's easy to calculate if you know the temp change. I think you'd get pretty close if you used the average temp over the length of pipe.
  • Like
Reactions: Bryce250


Minister of Fire
Feb 8, 2020
Central MA
The screws also defeat the purpose of the storm collar by creating a leak point. I'd take them out and replace the storm collar.
  • Like
Reactions: Bryce250