Available with catalytic converters

Some models extend onto the hearth while others stay flush with the front of the fireplace. Most have tight-fitting glass or metal doors and built-in circulation features. The most efficient models supply combustion air from outside the house, and virtually all inserts are controlled-draft units with manually or thermostatically controlled air inlets. Some units are also available with catalytic converters for improved efficiency.

Glass doors, heat exchangers, dampers and flue sealers can also up the energy efficiency of an existing fireplace, but don't expect too much. According to the Department of Energy, those devices combined could only improve efficiency by some 10%.

Custom fireplaces

Fireplaces can be customized with a variety of options

For instance, gas fireplaces feature three different kinds of logs: vented logs that provide a realistic burning wood look with less heat; ventless logs, which produce a yellow flame with a high degree of efficiency; and partially vented logs which provide a middle ground option in warmth, appearance and efficiency. Other options for fireplaces can include a matching tile hearth, a gleaming brass tool set, etched glass face or even a remote control for couch potato fire starters.

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.

Prefabricated Fireplaces

Many newer fireplaces are prefabricated from metal and installed in wood-frame walls. They generally have a metal shell and a brick-lined firebox.

Prefabricated fireplaces, also known as zero-clearance fireplaces, are highly insulated, so they can be installed within an inch of combustible materials, such as wall framing. They are preferred in new construction because they're much lighter in weight, are faster and easier to install than standard masonry units, and are energy efficient.

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.