  Small self-contained quantum thermal machines function without external
source of work or control, but using only incoherent interactions with thermal
baths. Here we investigate the role of entanglement in a small self-contained
quantum refrigerator. We first show that entanglement is detrimental as far as
efficiency is concerned---fridges operating at efficiencies close to the Carnot
limit do not feature any entanglement. Moving away from the Carnot regime, we
show that entanglement can enhance cooling and energy transport. Hence a truly
quantum refrigerator can outperform a classical one. Furthermore, the amount of
entanglement alone quantifies the enhancement in cooling.
