Cul Es La Estructura Organizacional Lineal? UODP Astria 60 inch HeatFlo 60 inch Flex Extension Kit HTFLO EK 5. Astria 60 inch HeatFlo 60 inch Flex Extension Kit HTFLO EK 5 Product Details The HeatFlo Extension Kit is required when the distance from the bottom of the register to the top of the appliance exceeds 70 inches. Features: Designed for Astria 60 inch Series fireplaces. Required for distances over 70 inches. Ensures proper installation and functionality. Designed specifically for Astria Fireplaces.