Frame Straightening with Heat

[KGBnut]

I've read a lot of threads about this (and the debate of cold straightening vs. heat straightening), but I am not sure I understand the procedure for straightening with heat. None of the discussions say anything about jacks, or levers, or anything else forcing the frame into shape once it is heated.

Am I to understand that you simply heat the underside of the frame, and then hit it with water to cool it rapidly, causing the metal on one side to contract?

I'm hoping to do my straightening without pulling the body. Can anybody speak to using this technique "body on?"

Thanks,

Ken