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A fan that withdraws air that is not returned to the central air-treatment center and is exhausted to the outside.
Illustrated Dictionary of Architecture Copyright © 2012, 2002, 1998 by The McGraw-Hill Companies, Inc. All rights reserved
A fan which withdraws air from a localized area or from a space in a building from which it is desired not to return the air to the central air-treatment system, as from a toilet.
McGraw-Hill Dictionary of Architecture and Construction. Copyright © 2003 by McGraw-Hill Companies, Inc.