How hot is too hot?

I've been trying to write a love scene for about a week.  In fact I have had a temporary case of writers block because I have been balancing on the edge of: how hot is too hot?

I wanted to give readers an idea of the heat, without anatomically describing too much action.  Don't get me wrong, I love a good smexy book.  I've read Fifty Shades of Grey and enjoyed it, but I don't think I'm at a place in my writing where I need to list out what goes where.

I want to show the feeling more than the action.  I want readers to run off with their imagination rather than be dictated how it should look in their heads.

I hope I managed to do that after the third re-draft of this scene, but only my readers will be able to tell once the sequel comes out. Oh, and I'm not saying who got it on.  You'll have to wait and read.