Why does cold air move from the poles to the equator and warm air from the equator move towards the poles?

Cold air moves downwards, where as hot air moves upwards. To be able to see that happening, if you open up your freezer door at home when your kitchen is hot, you will be able to see the cold air falling to the floor and your toes might get cold. This is the reason that people say how under floor heating is a muc more economical way to heat a room, due to the fact that the floor gets heated first and will retain some of it's heat. The heat that is produced from radiators leaves the metal and moves straight up, therefore heating the top of a room first, and you would need to heat a room for a longer time before feeling the heat at a constant temperature all the way to the ground.