1.   Air is heated and then circulated through large ducts to all parts of the house.

2.   On the craggy heights of a mountain range the air is heated on a slope.

3.   And the slight extra warmth in the air means the furnace uses less energy heating the air before pushing it back into the rooms.

4.   As the energy in a lightning stroke quickly heats the air several thousand degrees, the air expands rapidly, creating the sound waves we hear as thunder.

5.   Before starting the fire, make sure the damper is fully open, then heat the air in the flue to create a stronger draft.

6.   A furnace first heats air, then a fan pumps the hot air through metal ducts to floor registers in various rooms in the house.

7.   A simple electric compressor circulates refrigerant the way a freezer or window air-conditioner does, then cools or heats the air to be distributed through the house.

8.   Air is heated by propane or kerosene burners to compensate for the cooling of the helium at night and its consequent loss of lift.

9.   Ah, the sunshine of May has finally dried out the world and heated the air just enough to enjoy the outdoors.

10.   Bryant tests the propane-fired burners, which will heat the air inside the balloon and keep it inflated while aloft.