Yes, firebacks increase heat from a fire. Don't know about percent. You notice the heat right away rather than the bricks behind the fireback getting it. A fireback also reflects light which gives heat and something of interest to look at reather than worn out bricks. This is especially true when the back is polished with stove black. Once applied, stove black makes cleanning a fireback easy to clean and polish in place. No need to remove it, just a light brushing with a wire brush does the trick.