To me, heat isn't all about what happens behind the closed door (the one that often stays closed in YA lit.) It's about everything that leads up to that. It's about the slow simmer that turns into the rolling boil of desire. Heat is about chemistry. It's about what brings two people together, what turns them on to each other. To me, sweet, nurturing romance is even hotter than down and dirty lust.
I know there are many out there who read a romantic story and go back to reread the - shall we say 'explicit' bits over again. But to me the real heat is in the parts that lead up to that. I want to reread the sweet sexy wooing bits, the scenes in which the characters' thoughts and actions act as a magnet to draw the other person in. I'm not saying the explicit elements aren't hot too. They are of course. But in my opinion, the relationshipy elements that create the path to the explicit elements are just as hot.
In YA circles there is a lot of talk about how far the characters can go. I personally believe there really aren't rules to this. Lots of folks say there are. But those rules have all been broken. I suppose if you want your book in every school library and in the school fairs, you've got to leave out the sex scenes. But truthfully you've got to leave out a lot more than that to get into those arenas. So I say let the truth of the story and the characters play out as each story demands. But in doing so, enjoy the fun in letting the heat show up long before it's played out in physical connections.
Where do you like to see heat in romantic stories?