You could buy a 2 kg laptop with a 45 W CPU, but then it'd barely be portable and after a few years the battery will last half an hour, what's the point.
What you want to know is called the thermal design power: TDP, and you can look up the data sheet for the CPU in the laptop to know what it is. 15-22 W is typical, 30-45 W what you find in "workstation" laptops and small desktops, 60-120 W in desktops.
It's not just cooling but also battery draw.
You could buy a 2 kg laptop with a 45 W CPU, but then it'd barely be portable and after a few years the battery will last half an hour, what's the point.
What you want to know is called the thermal design power: TDP, and you can look up the data sheet for the CPU in the laptop to know what it is. 15-22 W is typical, 30-45 W what you find in "workstation" laptops and small desktops, 60-120 W in desktops.