FS4 Noritz 4" Diameter Stainless Steel Fire Stop The FS4 vertical stainless steel single wall firestop adds another level of protection to your home. The FS firestop piece continues the durable easy to install stainless steel design seen throughout the Noritz N-Vent series. As part of the N-Vent series this product is approved for tankless and boiler stainless steel exhaust installations, enabling you to know you've made the right choice in both form and function. Firestop: Noritz leaves nothing out when it comes to you and your homes safety. The FS4 firestop enables your opening to maintain it's in place fire-resistance rating, while doing its job as an integral part of the fire resistance system. In addition, the piece is part of the N-Vent series so it's approved for tankless and boiler stainless steel exhaust installations, enabling you to know you've made the right choice in both form and function.Stainless steelVenting series - 4" SUS