Standard for Type BH Gas Venting Systems
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.