Stove Pipe - Horizontal Max Distance?

From insulated Tee - I need to go six feet
Direction say "not to exceed 24 inch"
What effect will six feet have on operations?
Harder to start fire?
Is cement board on ceiling considered combustible?

It will reduce the draft, and may cause condensation issues.

The cement board is typically an acceptable fire protection, if you install it with 1" spacers behind it. Zero-clearance board is preferrable (2" thick mineral wool board), and is rated for (as the name implies) zero clearance to the flue pipe. Just use fender washers and decently-long sheetrock screws.

Joe

Thanks Joe - I will be coming out of tee at 30 deg for the first four feet
then stright into stove