The Cannulas Termination Grill prevents foreign objects from entering a venting system and causing an obstruction. Obstructions can reduce efficiencies or cause your furnace or water heater to shut down. The Cannulas termination grill will not rust due to acidic vent gases is more difficult to flash freeze than metal screens and has no sharp edges, unlike metal screens. Applications: gas water heater exhaust, high efficiency furnace exhaust, high efficiency furnace air intake.