QUESTION: What exactly is hot viewpoint? How is it different from other types of viewpoint?
Hot viewpoint is about the viewpoint character's emotional reaction to what is happening. Hot viewpoint is full of sensual details, strong emotions, and important/dangerous/violent actions. Most hot viewpoint moments are action scenes full of adrenaline, love scenes, or physical or emotional fight scenes which can include an argument between characters.
Cold viewpoint has almost no emotion involved. It’s a simple recital of facts or what’s happening.
Warm viewpoint is halfway between them with emotions of importance, but not extreme importance.
COLD: Pamela glanced at the doors' numbers as she passed them. Room 82 should be just ahead.
WARM: Pamela smiled as she glanced at the hotel room numbers. Tom said he's be in in Room 82. He'd promised her champagne, roses, and a night of passion. A night to remember. She could hardly wait.
HOT: The slight cheesy stench of the alien made Pamela's nose twitch as she leaned against the hallway wall. Her hands were sweating so much she feared she'd drop the Colt she held in her right hand. With a quick prayer for courage, she eased toward Room 82 and kicked in the door.
For a writer, it's not so important to know the difference in an intellectual way, but to understand it instinctively as we write. If we are inside the character and feel what she feels, we are more likely to get it right.