  Evidence has accumulated for an as-yet unaccounted for source of heat located
at shallow depths within the accreted neutron star crust. However, the nature
of this heat source is unknown. I demonstrate that the inferred depth of carbon
ignition in X-ray superbursts can be used as an additional constraint for the
magnitude and depth of shallow heating. The inferred shallow heating properties
are relatively insensitive to the assumed crust composition and carbon fusion
reaction rate. For low accretion rates, the results are weakly dependent on the
duration of the accretion outburst, so long as accretion has ensued for enough
time to replace the ocean down to the superburst ignition depth. For accretion
rates at the Eddington rate, results show a stronger dependence on the outburst
duration. Consistent with earlier work, it is shown that urca cooling does not
impact the calculated superburst ignition depth unless there is some proximity
in depth between the heating and cooling sources.
