Platform for chimney support

[Jafo]

I don't think it will be a problem. I have a coupler on mine, but closer to the top. Perhaps some others could chime in?

[hierony]

I have known one or two pipes/couplers that weren't all that great--the joint wobbled a bit. Probably just parts made as cheaply as possible with loose specs. So I'd check how well the coupler holds pipes together, at the store if possible & again with your pipes.

Also note, there's less torque (from the top) on the coupler the higher you put it. Putting it in the exact middle maximizes the torque on the coupling in some situations. But if it's sturdy to begin with probably not something to worry about.

[Vermont2014]

Thanks for the responses. Once I put the section section up I will see how study it is.
Guess I could fill the first 10' section with concrete if worst comes to worse?

[Jafo]

Providing your coupler is tight and sturdy, it should be fine.