Stove flue pipe expansion

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vti-chris

Member
Jan 23, 2012
12
Cyprus
I installed my SS flue pipes on my woodstove and added three screws on each joint plus high temp mastic to seal it better. I supported the flue with the wall brackets so the whole setup is solid. I've read around and found that stainless steel expands 3/8" every 3ft.

-Where does that expansion goes if everything is screwed together?

- The only joints that aren't screwed together are the telescopic pipe and the stove top joint. After lighting it up for the first time i noticed that some paint was removed from the telescopic pipe which moved 1/2" and then went back to it's original position after cooling.
Should i leave it as is to expand freely or screw it down?
I thought of leaving if as is and cover the scratched pipe with another 1"piece of pipe which will seat on the larger diameter part of the telescopic flue and slide with it up and down.
IMG_20201102_065348.jpg
 

Mech e

Feeling the Heat
Feb 26, 2019
385
NorCal
www.dtengineer.com
304 stainless expands at a rate of 9.6 x 10 ^-6 in/in F. For a 3' section of pipe, this would equate to .00035" / degree F.

Additionally, the stove will expand as well as it heats up.

This expansion and contraction requires give in the system, and the slip joint is it.

How long is the stove pipe between the stove and ceiling? Is this single wall pipe?
 
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vti-chris

Member
Jan 23, 2012
12
Cyprus
Stove to ceiling 8 ft. single.
Wall bracket.
Then 11ft double insulated pipe through the second floor and a second wall bracket through the ceiling of the 2nd floor.
Finally off to the roof for another 8ft and a 3rd V shape stand/bracket to protect it from strong winds.
 

Mech e

Feeling the Heat
Feb 26, 2019
385
NorCal
www.dtengineer.com
Okay, doing some quick calcs (approximations) for pipe and stove expansion. I come up with about .3"-.375" total expansion (if it is more than that my average temperature guesses are just low). The slip connection is what deals with this. If you don't like the paint being scrapped off, you might give double-wall pipe a try. The outer pipe wall does not get nearly as hot and in my experience is a bit looser fit at the slip joint, so it probably won't scrape off the paint with the reduced expansion.
 

Mech e

Feeling the Heat
Feb 26, 2019
385
NorCal
www.dtengineer.com
My concern is whether this expansion needs to go somewhere or should we screw everything together rock solid?
The expansion is a physical property of the metal and needs to go somewhere. I would not screw the slip fit connection together.