Elf Sternberg

Most laptops these days put the ethernet card in low power mode (essentially switched off) when it's not got a cable plugged in. So, there's one source of heat you don't have at home.

Another is that if you are using it off battery at home the system will use assorted power management features (adaptive CPU clock speed, for example) to reduce power consumption. Running of the mains usually these power saving features are disabled and more power is consumed and more heat generated.