What to do with an inactive chimney flue? What is the best way to seal it?

[Dmitry]

I have three flues in my chimney. The one is for oil furnace , the middle is for wood insert on a main floor and the last one is from fireplace in a basement we don't use and don't intend to use for years . It's about 25'' tall.
What is the best way to seal it with possibility of opening it if needed in 10 -20 years ?

 

[Fastdonzi]

I have the same thing, I capped my unused ones with sheet metal and silicone... its been up there for 15 yrs....

 

[jb6l6gc]

I have the same thing, I capped my unused ones with sheet metal and silicone... its been up there for 15 yrs....

Yep thats the same way mine is capped.

 

[Dmitry]

Do you put something to cover the opening in a basement? I think it would still suck some heat even with the cap on.

 

[JA600L]

Seal both ends.