  We discuss finite volume errors in our calculations of $B_K$ using improved
staggered fermions on the MILC asqtad lattices. Using GPUs, we are now able to
extrapolate using next-to-leading order (NLO) staggered SU(2) chiral
perturbation theory including the finite volume corrections arising from pion
loops. We find that the impact of FV fitting is very small, giving a 0.5% shift
in the continuum limit.
