Open fireplaces are not at all efficient; in fact, they pull more heated air out of your house than radiant heat they put into your room. A wood insert drastically reduces the air loss associated with an open fireplace, and also adds inexpensive radiant and blower-assisted hot air heat to your living area.
Best of all, cord wood is a “Green” fuel: using wood for a heat source is a carbon-neutral process, and is a renewable energy resource. As trees grow, they absorb carbon dioxide from the atmosphere. Burning firewood produces the same amount of carbon dioxide as it has absorbed during its life cycle.