I'm looking into running a longwire with an antenna tuner for my 100W HF station and I'm a bit confused whether I need to also use a balun with the tuner. I'd like to keep the rf out of the shack.

Shack is in the basement. Coax feedline running up to the longwire that begins near the top of my chimney. Plan to use a counterpoise as well.

Any help/suggestions greatly appreciated.