Peltier modules do an excellent job of actively transferring heat from the cold side of the module to the hot side. However, once the heat has been transferred, if not removed, the Peltier module will heat up. This is because the electricity input into the module used to transfer heat across the device also has the unfortunate side effect of creating a considerable amount of heat. While very effective in transferring heat, Peltier modules typically consume more energy (in the form of electricity) than they transport (in the form of heat). For this reason, it is necessary to connect the module to a radiator such as a heat sink to efficiently disperse the emitted heat. A Peltier module fitted between a radiator and a heat extractor like an aluminum block for use as a cooling device is called a cooler unit.