flue block

chimney block

A solid concrete masonry unit with curved faces, intended for use with other similar units in laying up a round flue.
McGraw-Hill Dictionary of Architecture and Construction. Copyright © 2003 by McGraw-Hill Companies, Inc.
References in periodicals archive ?
The inquest was told the living room door had been closed and no windows were open and with the chimney flue blocked there was nowhere for the fumes to escape.
Experts found that a flue blocked by a fallen brick had been spewing deadly fumes into the family home in Colchester, Essex.