Vertical draft

Vertical draft is when hot air is sent up through a tall chimney (or something like a tall pipe). The air rises because hot air is less dense than cold air, so it takes up more space and floats up. When the hot air rises, it creates a vacuum and sucks the colder air in from the bottom, which is why it's called "vertical draft". This helps to create a steady flow of air, and with it, the heat from the hot air can help warm the surrounding area.