Active laptop coolers utilize small
fans to enhance airflow around the laptop's chassis, aiding in the
convection of heat away from the device. These coolers typically incorporate between one and six fans, helping regulate temperature. Coolers typically run on power drawn through one of the laptop's
USB ports, with some models featuring integrated
USB hubs so as not to consume one of the laptop's often limited number of USB ports. Some active coolers draw heat from the underside of the computer; others work in the opposite way – by blowing cool air towards the machine. The fan speed is adjusted manually or automatically on certain models and on others stays at a fixed speed. Poorly designed coolers may use fans which draw more current than allowed by the USB standard. Without correct protection, such devices can cause damage to the USB power supply. Inside the laptop, the USB power-supply has to output an additional amount of
watts for the USB-powered fan, thus generating a small amount of additional heat. This additional heat generation is usually insignificant in relation to the amount of heat a fan moves away from the laptop. Some high-end active coolers have
blowers instead of fans, with
filters to stop dust from entering the laptop, and have
seals between the cooler and laptop surfaces to prevent recirculation of hot air from entering the laptop. ==Passive coolers==