Answer:
The movement of air in a hot-air balloon makes it rise into the sky.
A house has high heating bills because the heat ends up in the attic.
Explanation: Convection is a form of heat flow where heat is transferred through fluids. When a gas or liquid absorbs heat, its density decreases and becomes less dense that is the reason why that hot air rises and cooler air sinks. Same with the concept of hot-air balloons and heat moving up on the attic.