Janitrol Model GMP 050,075,100 or 125
These furnaces were installed from the late 80s to present. They are 80% efficient furnaces and they vent with metal pipe. They are induced furnaces, meaning they use a fan to extract the burned gasses from the heat exchanger and into the vent. The video below gives sequence of operation of an 80% efficient furnace and the model used is a Janitrol GMP 075 model.