1. SCOPe 1.1 These requirements cover the design, construction, and performance of gas
venting systems intended for negative or positive pressure venting of gas-fired
appliances producing flue gases having temperatures as specified in Clauses
1.2 and 1.3. 1.2 Class I venting systems are suitable for gas-fired appliances producing
flue gas temperatures of more than 135°C but not more than 245°C. 1.3 Class II venting systems are suitable for gas-fired appliances producing
flue gas temperatures of 135°C or less. 1.4 Class II venting systems are further classified into four temperature
ratings as follows: A Up to and including 65°C; B Up to and including 90°C; C Up to and including 110°C; and D Up to and including 135°C.