Heat vs. Temperature

Heat becomes "active" only when it transfers from a higher temperature to a lower one such as occurs when a hotter substance thermally communicates with a lower temperature substance. British Thermal Units, or BTU's are common units for heat (but don't expect to see a BTU). Temperature, on the other hand, is quite different than heat. It is a relative measure of the average speed of the atomic constituents of a substance; degrees Celsius or degrees Fahrenheit are familiar temperature scales. Therefore, "cooler" just means the average atomic speed of a substance is slower and than one that is "hotter". Thus, heat is transferred only as a result of the slowing-down of the constituents of the hotter substance and a speeding-up of the constituents of a cooler substance as they come into thermal contact. Since the natural flow of heat is from hot to cold (much like water at a higher level will naturally flow to a lower level), the job of air conditioning is to reverse this thermal flow by causing something already cool to become cooler.

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