I am turning my attic into a bedroom, I am installing 2 electric hard wire heaters 240v-4.2 amps each,6 outlets, 2 ceiling lights,1 ceiling fan. I am confused as to what size the feeder cable should be, and could I run it from the basement through a race (which has the stand pipe in it) to the attic about 100 feet?

A 30, 40 or 50 amps sub would be fine. A 50 would be most common and also leave room for some future expansion.

Using a stand pipe chase is a very typical way to run from basement to attic. Be careful that there is nothing to damage the cable when pulling.

Thanks stanfortyman