Reality: Traditional fireplaces add ambience, but they also suck most of your heated air right up the chimney. You can fix that. Fireplace inserts decrease the amount of heated air lost by up to 60 percent and are available for both wood- and gas-burning fireplaces. The inserts include insulated doors and a vented surround that lets you control air input and heat output. Even better are super-high-efficiency wood- or pellet-burning stoves, some of which are sold as inserts that can be installed in your existing firebox.