Air is not a convenient medium for transporting
heat. A cubic foot of air weighs only about 0.074 pounds
(0.34 kg) at standard conditions (70°F; 1 atm.). With a
specific heat of about 0.24 Btu/lb°F (0.14 joule/C), one
cubic foot can carry less than 0.02 Btu per degree Fahrenheit
temperature difference. By comparison, a cubic
foot of water weighs 62.4 pounds and can carry 62.4
Btu/ft3.