Download the Variance Conditions for Temporary Use of Existing Unlined Chimneys (B149.1-05, section 8.12.2) - Here (http://hvactechgroup.com/files/advisory/fs11007.pdf)
QuoteClause (8.12.2) - Before replacing an existing appliance or connecting a vent connector to a chimney, the chimney flue shall be examined to ascertain that the chimney
(a) is properly constructed;
(b) is lined with a tile or metal liner;
(c) is clear and free of soot, creosote, or obstructions;
(d) will effectively conduct the products of combustion outdoors; and
(e) is sized in accordance with Clause 8.13.