The Navien 390mm horizontal flue terminal kit made of PPS (Polyphenylene Sulfide) and PVC (Polyvinyl Chloride) is a specialzed component designed for venting exhaust gases horizontally from a condensing boiler through an external wall. The 390mm refers to the length of the flue pipe included in the kit. These materials are chosen for their chemical resistance, durability, and ability to withstand the acidic condensate produced by high-efficiency condensing appliances.

So to conclude the Navien 390mm horizontal flue terminal kit made of PPS/PVC provides a durable and efficient solution for venting exhaust gases horizontally through an external wall. It is especially suitable for condensing boilers due to its resistance to high temperatures and corrosive condensates, ensuring safe and effective ventilation of exhaust gases.