  We study the thermoelectric properties of three-dimensional topological
insulators in magnetic fields with many holes (or pores) in the bulk. We find
that at high density of these holes in the transport direction the
thermoelectric figure of merit, ZT, can be large due to the contribution of the
topologically protected conducting surfaces and the suppressed phonon thermal
conductivity. By applying an external magnetic field a subgap can be induced in
the surface states spectrum. We show that the thermoelectric efficiency can be
controlled by this tunable subgap leading to the values of ZT much greater than
1. Such high values of ZT for reasonable system parameters and its tunability
by magnetic field make this system a strong candidate for applications in heat
management of nanodevices, especially at low temperatures.
