Preface This is the third edition of CSA B255, Mechanical flue-gas exhausters. It supersedes the previous editions published in 1981 and 1973. Scope 1.1 This Standard applies to mechanical flue-gas exhausters intended to be installed in a flue pipe, breeching, or chimney and serving appliances burning natural gas, propane, or fuel oil. 1.2 This Standard covers the mechanical and electrical features of mechanical flue-gas exhausters for indoor or outdoor installations. 1.3 This Standard classifies mechanical flue-gas exhausters as: a) Type 1 is suitable for maximum operating temperatures of 300 °C (575 °F); b) Type 2 is suitable for maximum operating temperatures of 550 °C (1000 °F); and c) Type 3 is suitable for maximum operating temperatures of 850 °C (1600 °F). 1.4 This Standard is not intended to cover mechanical flue-gas exhausters with motor ratings exceeding 375 W (1/2 hp). 1.5 This Standard is not intended to cover mechanical flue-gas exhausters for use with incinerators, incinerating toilets, or condensing type or solid fuel burning appliances. 1.6 This Standard may also be applied to such equipment as air circulators and boosters. 1.7 The values given in SI units are the units of record for the purposes of this Standard. The values given in parentheses are for information and comparison only. 1.8 In this Standard, °shall° is used to express a requirement, i.e., a provision that the user is obliged to satisfy in order to comply with the standard; °should° is used to express a recommendation or that which is advised but not required; and °may° is used to express an option or that which is permissible within the limits of the standard. Notes accompanying clauses do not include requirements or alternative requirements; the purpose of a note accompanying a clause is to separate from the text explanatory or informative material. Notes to tables and figures are considered part of the table or figure and may be written as requirements. Annexes are designated normative (mandatory) or informative (nonmandatory) to define their application.