An open fronted (no glass) convector box is a box within another box, with a gap around the internal fire box to allow convection heat to transfer into the room from the back of the fire. This is more efficient than an open fire, due to having a restricted throat area with a damper allowing you to regulate the chimney draft. This stops some of the heat going up the chimney, but it is not as efficient as a stove. There are wood burning and gas convector boxes available.