Foundation Steaminess Rating
Actually, let's make that negative G. Foundation has all the steaminess of a pile of woodchips lit on fire in a particularly dry desert. Not a single character in the novel seems even remotely interested in sex or romance or even members of the opposite sex (or same sex, for that matter).
The only exception is Hober Mallow, who might be something of a playboy. All the same, Disney cartoons have more sexual content than this novel. Come on, have you seen Jasmine's outfit? And don't even get us started on Megara's swagger.
So, unless you find detailed discussions of intergalactic trade particularly, um, engaging, you can safely rate Foundation G.