A good cast iron fireback can protect the back of your fireplace wall while adding to the heating efficiency of the unit. The back of your fireplace can absorb a lot of soot and grime over time. This isn't a danger, but it can be a hassle to clean if you want to keep things looking new and fresh. This can especially be useful when it comes time to sell your home. A fireback will help preserve the look of your masonry fireplace so that it's easier to clean the firebox up for when potential buyers come looking.
But the real strength of a fireback is in increasing the heating efficiency of your fireplace. A cast iron fireback reflects the heat of the fire into the room. More heat goes into the living room, reducing your heating bill; and less heat goes up the chimney.
Don't be fooled by the word "reflects," though. We're not talking about something shiny here. Nothing that sits in the back of your fireplace can stay particularly shiny for long anyway. No, the point isn't to reflect light, but heat. And heat reflection occurs when a dark, metal object absorbs the heat from the fire and begins to radiate it out again.
You don't have to be a physicist to have a sense of how this works. If you leave a piece of wood and a piece of metal out in the sun, you know which one will become hot to the touch. Firebacks take advantage of this physics to heat your home more efficiently from your fireplace.
The simplest fireback is installed by simply placing it in the firebox and leaning it against the back. Firebacks are sufficiently heavy that this is really all they need. But you may want some additional support anyway, just for piece of mind. Or you may feel that leaning a fireback makes the whole firebox look slightly cockeyed, destroying the clean lines and right angles. In that case, you can get a set of feet to hold the fireback upright and in place. These feet will also move the fireback closer to the fire. In a large fireplace, this can be an advantage. You don't want the heat of your modest fire being lost in the cavernous depths.
Firebacks come with all sorts of designs to them. The simplest come with no design at all. They're just plain panels, perhaps with ridges or scallops along the borders. You can get a simple fireback with rows of stars, the same as you'd see on an American flag. For that matter you can actually get one with an American flag design.
And from there, we leave simplicity behind. Continuing the patriotic theme, you can get a fireback that has the first dozen or so lines of the US Constitution engraved on it. You can get firebacks with horses or eagles or trees or shells or Greek or Roman gods and goddesses. You can get a fireback with a Parthenon in Athens or a famous coat of arms from England.
If you really want to go all out, you can get different firebacks for each season of the year and alternate them accordingly. Summer scenes give way to fall which give way to winter which give way to spring. You can even get your fireback personalized with special names or dates.
Depending on the size of your fireplace and the ornateness of the design, a fireback can cost anywhere from $75 to $300.