I just gotta get in to this little debate. Not only does hot air rise but heat rises. Those overhead LP gas heater reflect the heat. Little different and not good for an example.

An old tractor or truly antique car. No water pump. How does it work. The hot water rises in the block. The hot water cools in the radiator and flows right out the bottom back into the block. No pump just heat or loss of heat making the water flow.

Leon