No wonder that about 70% of all hearth products—fireplaces, inserts, and artificial log sets—now burn gas. Unlike old decorative gas fireplaces, today's gas inserts are heat-producing dynamos that use natural gas or propane to power a steady flame dancing on fake logs, decorative modern glass chips, or stones behind a sealed glass face.
Vented Gas Logs Because vented gas logs are designed to operate with an open chimney, flue, or damper, most of the heat that they generate escapes out the chimney, meaning that they are more decorative than actually heat efficient.
Installing a set of vent-free logs or a full-blown Gas Fireplace Insert into the opening would provide quite a bit of heat into the area. If, in fact, you do not have a wood burning fireplace..but a vented gas burning one, then you have been saddled with an inefficient model and there may be little you can do.
As far as blower fans go, I am of the opinion that they do more to move heat through the space then provide more heat or efficiency from the fireplace. This of course depends on the heat output of the fireplace to begin with of course. Source: work at a gas/wood fireplace distributor & builder contractor. Sorry for typos etc.
How to Make Your Fireplace More Efficient Chimney cap dampers close the entire top of the chimney, so they reduce heat loss when the fireplace is not being used, but don't improve efficiency
All About Gas Fireplaces Both inserts and built-in fireplaces are reliable heat producers, filling your room with a mix of warm air and radiant heat. Log sets are usually more for looks than warmth. With each gas fireplace type, you have a choice between models that vent the flames' fumes