Why would someone choose to do this?
Well, primarily because the insert can increase the amount of heat put off, reduces the number of pollutants put into the air, and escalates the efficiency of your fireplace.
These inserts have what is called a firebox, which is typically surrounded by fireproof steel or cast iron. It can change the appearance of your fireplace and give it a unique or updated look. It comes with a faceplate which is placed in the space between your fireplace opening the outer surround of the insert. You will likely have a variety of decorative faceplates from which to choose.
There are generally 3 types of gas inserts you can consider: Direct Vent, Vent-Free (or ventless) or a B-Vent. What are the differences?
A direct vent insert has a unique venting system that can travel up through your existing chimney or even vented out of a side wall of your home.
This is the type of insert in my own living room. The venting system is actually two-pipes- a small one inside a bigger one. It will be more energy efficient than your wood-burning masonry fireplace.
A vent free gas insert is also attached to the gas line, but does not require a chimney or wall out-vent to operate. You can locate these with a variety of features, such as your choice of logs (oak, pine, driftwood, etc.), remote on and off features, firebrick or ceramic look, thermostats and blowers, and other options.
A B-vent gas fireplace insert actually takes air from your living area for combustion and then vents that air through a vent attached to your chimney, or possibly your roof, or a wall in the side of your house.
Although less efficient than your other two options above, you still will most likely improve the energy efficiency as compared to your older wood burning masonry fireplace.
Check out your multitude of options, and consider a gas fireplace insert to brighten up your living space today.