ULC 635:2016

This National Standard of Canada covers lining systems for existing masonry chimenys, which may or may not incorporate a liner of fire-clay tile, and existing factory-built chimneys and vents. Lining systems are classed as follows:
Class 1 - For the venting of gas-fired appliances where the temperature of the flue-gas products in 135 °C or above, but does not exceed 245 °C;
Class 2 - For the venting of oil and gas-fired appliances where the temperature of the flue-gas products does not normally exceed 300 °C; and
Class 3 - For the venting of oil-, gas- and solid-fuel fired appliances where the temperature of the flue-gas products does not normally exceed 650 °C.