Three different styles of gas fireplaces  

The direct vent model, the top vent design or the vent-free model. The direct vent gas fireplace uses two pipes that lead directly to the outside. One pipe uses combustion air from the outside while the other vents the exhaust gas.

The top vent design can be installed into an existing fireplace and uses the metal or brick chimney as the exhaust vent. The combustion air for top vent fireplaces is drawn from inside the home. The vent-free gas fireplace model uses no exhaust vent. This style includes an oxygen-depletion sensor that turns off the gas if it senses a dangerous lack of oxygen inside the house.

Fireplace inserts are heavy, often weighing more than 400 pounds. Since wood burning inserts need to be removed when the chimney is being cleaned and maintained, they can be awkward and heavy to handle. It is a job best left to a professional chimney sweep. In some cases, however, you do not have to remove the insert to clean the chimney. The insert can stay in place during cleaning if you install a full relining collar, a stainless steel pipe that connects to the insert and goes to the top of the chimney. You might need to purchase accessories such as a blower, glass door, or catalytic combustor to go with the insert.

New masonry fireplaces have come a long way since the days when they provided more ambience than warmth. Today's models are much more energy efficient, and some European models can heat an entire small home. The cost varies, depending on factors such as the type of material used, particularly on the fireplace face; or hearth (brick, stone, concrete, tile, marble or wood) or whether it's a pre-fabricated unit, and other factors such as chimney liners.