space heater

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

• noun A usually portable appliance that generates heat by electricity or by burning kerosene or oil to warm a small area or room.

from the GNU version of the Collaborative International Dictionary of English.

• noun a portable heating device used for warming the air of a single room; -- it may be electrical or use a combustible fuel.

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

• noun A portable heating appliance used to warm an area or room.

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

• noun heater consisting of a self-contained (usually portable) unit to warm a room