  We study the thermoelectric properties of three-dimensional topological
insulators with many holes (or pores) in the bulk. We show that at high density
of these holes the thermoelectric figure of merit ZT can be large due to the
contribution of the conducting surfaces and the suppressed phonon thermal
conductivity. The maximum efficiency can be tuned by an induced gap in the
surface states dispersion through tunneling or external magnetic fields. The
large values of ZT, much higher than unity for reasonable parameters, make this
system a strong candidate for applications in heat management of nanodevices,
especially at low temperatures.
