  We report detailed Seebeck coefficient, Hall resistivity as well as specific
heat measurement on Ca$_3$Ir$_4$Sn$_{13}$ single crystals. The Seebeck
coefficient exhibits a peak corresponding to the anomaly in resistivity at
$T^*$, and the carrier density is suppressed significantly below $T^*$. This
indicates a significant Fermi surface reconstruction and the opening of the
charge density wave gap at the supperlattice transition. The magnetic field
induced enhancement of the residual specific heat coefficient $\gamma(H)$
exhibits a nearly linear dependence on magnetic field, indicating a nodeless
gap. In the temperature range close to $T_c$ the Seebeck coefficient can be
described well by the diffusion model. The zero-temperature extrapolated
thermoelectric power is very small, implying large normalized Fermi
temperature. Consequently the ratio $\frac{T_c}{T_F}$ is very small. Our
results indicate that Ca$_3$Ir$_4$Sn$_{13}$ is a weakly correlated nodeless
superconductor.
