How do radiation convection?

Answer 1

Being designed to radiate (give out/emit etc) the thermal energy of the hot water inside them, a convection radiator will heat the air above itself. As the gas is heated it expands (thermal energy is "converted" to kinetic energy and hence the molecules move faster and hence expand), as the gas expands it's density decreases and so it rises above the cooler, denser gas surrounding it.

As more gas is heated the gas will diffuse across the roof of the room and gradually cool.

When the gas is initially heated it's original volume is filled by in-rushing cooler gas, this in turn is heated, eventually the original gas, which has recently cooled and descended, is heated once more thus forming a convection current.

One of the problems with convection heating of any kind is the tendency for the central areas of large spaces to remain unheated, furthermore longer spaces may not be heated at the far end from the heat source as the gas cools and descends before travelling the length of the space.