The I 520 FRL. The Jøtul I 520 Series is a flexible insert system that consists of four inserts. You can choose whether you want glass on one, two or three sides. The design glass wood burner 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 firebox is large, it works well even at 3.5 kW effect.