When summer fronts were first made, in the mid- to late 1800s, homeowners relied on fireplaces fueled by wood or coal to heat their homes. In warm seasons, when the fireplace wasn't in use, they would cover the opening so as not to see an ashy pit. Come winter, they'd simply remove it and spark up a fire.
That changed in the thermostat age. Today, the fronts are often left in place year-round on nonworking fireplaces that have been sealed off to prevent a home's cooled or warmed air from escaping up the chimney. In this case, the filigreed or figural fronts offer a decorative way to conceal the brickwork used to fill in the firebox.