A wood-burning fireplace insert is a metal box that fits inside your existing masonry fireplace opening. A decorative flange fits around the outside edges so that no gaps appear between the unit and the sides of the fireplace. A new metal chimney liner is required to carry combustion gases and smoke up through your chimney.

Fireplace inserts have clear heat-proof glass doors. The best designs circulate air within the firebox in a way that helps keep the glass clean.

Wood-burning fireplace inserts heat 1,000 to 3,000 square feet, depending on their size. Talk to your insert dealer about the size of your existing fireplace and what heating capacity you can expect from an insert.

Inserts cost $3,000 to $4,000, including installation and a chimney liner.