ULC 636

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 2 and 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.

NOTE: Compliance of a venting system with this Standard does not imply that the venting system is acceptable for use on a gas appliance without supplemental tests in the applicable gas appliance standard resulting in the listing of the appliance for use with the specific type(s) of venting system covered by this Standard.