  The origin of atmospheric heating in the cool, magnetic white dwarf GD 356
remains unsolved nearly 40 years after its discovery. This once idiosyncratic
star with $T_{\rm eff}\approx7500$ K, yet Balmer lines in Zeeman-split emission
is now part of a growing class of white dwarfs exhibiting similar features, and
which are tightly clustered in the HR diagram suggesting an intrinsic power
source. This paper proposes that convective motions associated with an internal
dynamo can power electric currents along magnetic field lines that heat the
atmosphere via Ohmic dissipation. Such currents would require a dynamo driven
by core $^{22}$Ne distillation, and would further corroborate magnetic field
generation in white dwarfs by this process. The model predicts that the heating
will be highest near the magnetic poles, and virtually absent toward the
equator, in agreement with observations. This picture is also consistent with
the absence of X-ray or extreme ultraviolet emission, because the resistivity
would decrease by several orders of magnitude at the typical coronal
temperatures. The proposed model suggests that i) DAHe stars are mergers with
enhanced $^{22}$Ne that enables distillation and may result in significant
cooling delays; and ii) any mergers that distill neon will generate magnetism
and chromospheres. The predicted chromospheric emission is consistent with the
two known massive DQe white dwarfs.
