  We theoretically study the conditions under which a spin Nernst effect - a
transverse spin current induced by an applied temperature gradient - can occur
in a canted antiferromagnetic insulator, such as ${\rm LaFeO_3}$ and other
materials of the same family. The spin Nernst effect may provide a microscopic
mechanism for an experimentally observed anomalous thermovoltage in ${\rm
LaFeO_3}$/Pt heterostructures, where spin is transferred across the
insulator/metal interface when a temperature gradient is applied to ${\rm
LaFeO_3}$ parallel to the interface [W. Lin ${\it et \; al}$, Nat. Phys. ${\bf
18}$, 800 (2022)]. We find that ${\rm LaFeO_3}$ exhibits a topological spin
Nernst effect when inversion symmetry is broken on the axes parallel to both
the applied temperature gradient and the direction of spin transport, which can
result in a spin injection across the insulator/metal interface. Our work
provides a general derivation of a symmetry-breaking-induced spin Nernst
effect, which may open a path to engineering a finite spin Nernst effect in
systems where it would otherwise not arise.
