What Are Decorative Gas Effect Fires? A 'Coal Effect Decorative Gas Fire' might best be described as an inset gas fire designed to give a low, but complimentary, heat level to a room. A Coal Effect Decorative Gas Fire is typically used in a room where an alternative heat source is also available. For example to compliment existing Central Heating These fires are designed to be fitted into a standard brick constructed chimney (Class 1 Chimney/Flue)