Closing the door on a normal, single-sided fireplace helps control the amount of heat it releases into the room. It also keeps ash and sparks from flying out if a strong draft comes down the chimney. However, double-sided fireplaces don't have a back side of solid stone or masonry like a one-sided model does. You may want to close one door to direct the heat -- but Chimneys.com warns that this causes fireplace glass to crack.
The draft created by a chimney helps pull away the smoke created by a fireplace. The air dynamics are different in a fireplace open on two sides, but many contractors fail to design the chimney to adapt to this change. Air drafts also blow smoke out of two-sided fireplaces easily because of the lack of a back wall to direct the smoke upward. Adding glass doors and allowing for better ventilation of outside air into the room help fix this problem, according to Hearth and Home.
All fireplaces produce a number of unpleasant smells due to the soot and ash that builds up in them. Double-sided fireplaces release more of these smells into the room when not in use due to the two openings that leak small amounts of air from around the doors. Sweeping out ashes and scrubbing off soot prevents the room from smelling musty or like smoke when the fireplace isn't in use. Having the chimney cleaned also cuts down on unwanted odors.
Fixing odors may be easy, but dealing with excess smoke and broken glass doors requires a greater investment. Increasing the height of a chimney for a double-sided fireplace increases the draw and prevents smoke from escaping into the room, according to Hearth.com. Installing a better fitting damper also helps control smoke ventilation. If you want to be able to close the doors on one side at a time, consider upgrading -- thicker glass with a higher heat resistance prevents dangerous glass explosions or cracks from heat damage.