he I 520 FR. The Jøtul I 520 Series is a cast iron fireplace insert system that consists of four fire inserts. You can choose whether you want glass on one, two or three sides. The design is timeless and the construction optimal and futuristic. Jøtul I 520 has enamelled burn plates which provide a light and airy flame picture. All glass has a heat reflecting surface that ensures cleaner glass and better combustion. Even though the insert is large, it works well even at 3.5 kW effect.