heat pump

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A device that warms or cools a building by transferring heat from a relatively low-temperature reservoir to one at a higher temperature.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun A device that transfers heat from something at a lower temperature to something at a higher temperature by doing work

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun apparatus that extracts heat from a liquid that is at a higher temperature than its surroundings; can be used to transfer heat from a reservoir outside in order to heat a building