Understanding your firebox style and how it performs will give us a better idea of what type of system will best suit you.
The firebox style is an intricate part of the fireplace system in whole. The way it is designed will indicate how much heat will be radiated into the room as well as determine how much fuel (wood) you will need to burn to generate the heat. They typically come in one of these styles:
Most fireplaces today are considered to have a “Traditional” style. The side walls of this style have very little splay or angle to them. This takes away from the amount of heat the firebox can radiate. Also, the rear wall of the firebox is normally flat and is almost as wide as the fireplace opening. In essence your traditional fireplace is truly just a large rectangular masonry box that puts enough heat back into the fire for combustion and up the chimney for draft, not much into the room.
A “Rumford” style firebox is tall with a shallow hearth depth. The throat is narrowed to eliminate turbulence and pull the smoke up the chimney with little heat loss. The rear wall dimension is one third the size of the fireplace opening which allows for the splaying of the sidewalls. The side walls are angled to radiate heat into the fire as well as back into the room for more efficient burning of the wood.
Prior Fire Firebox
A “Prior Fire” style firebox is similar to a Rumford firebox except the rear wall has a 4 inch apex hump or about a quarter of the way up. It is designed to radiate heat downward towards the fuel (wood) as well as radiate more heat into the room.