The heat is completely overwhelming, even just a oft warmth, but it's what his body needs, to warm up and get functional. Survive the shock. It's easier when Klaus is touching him because it's more than just the overwhelming warmth. It's familiar, old memories and old comfort.

He looks as Klaus strips; he's seen Klaus naked so many times that it fails to have any real impact, but then Klaus is in with him and he leans back into the touch, hugging his thighs to his chest.

Then he leans back instead, to rest his back to Klaus' chest and slid down a bit more into the water. He's still trembling, but it's starting to ease off as the heat gets into him.