Efficiency Ratings
Fireplaces today are built for efficiency. Like a standard furnace, gas fireplaces have a Btu (British thermal unit) rating. Btu ratings measure the amount of heat produced by the fireplace. Models should also have an Annual Fuel Utilization Efficiency (AFUE) rating. This system is used to determine the fireplace's efficiency. AFUE ratings are similar to gas mileage figures for cars—the higher the rating, the more efficient the fireplace. An AFUE figure takes into account all of the energy used as the appliance cycles on and off, and gets up to a target temperature. Another efficiency measure is the steady state efficiency rating. The steady state figure rates efficiency while maintaining a constant temperature. Be sure when comparing fireplace ratings that the numbers are from the same scale. Typically, steady state rating will be higher than the AFUE rating, which takes into account the unit's efficiency at startup and as it reaches the desired temperature.

Three Types of Fireplaces
There are three options to consider when installing a gas fireplace. Depending on your space and existing home, inserts, direct-vent, and vent-free models are available. Most gas models can be converted to use propane, and many wood burning models can have gas jets added for heat-boosting potential on extra chilly days and nights.

Fireplace Inserts
Inserts are designed to fit in an existing wood burning fireplace and be vented through an existing chimney via a special vent pipe that carries the fumes to the outside. Inserts are comprised of a metal firebox that contains the decorative logs and gas jets. The inner firebox is surrounded by a layer of air and a second metal layer to contain the air that is warmed by the inner firebox. When ignited, the fireplace insert draws in fresh air, warms it between the two boxes, and sends it up through the top of the box and into a room. Air for combustion air is drawn in from a second vent pipe (sealed combustion) or, in some cases, from the room itself. Outside air vents may also be installed to provide combustible air from outside. Many models offer a fan or blower to boost the delivery of warm air to the room and encourage a more even distribution of heat.

An insert can be made to look like the masonry around it. "We also make fireplaces out of ceramic fiber, which we market as 'Firebrick,'" says Ross Morrison of Heat-N-Glo. "These fireplaces and inserts are produced from a mold that can be done to any shape and resemble real brick, giving the consumer a true masonry appearance. It's also extremely good insulating material. So rather than heating air behind the firebox, it pushes that heat out the glass front in the form of a much-improved radiant heat." One of the greatest features of any glass-front fireplace is the radiant heat with which it warms the room. Radiant sources provide steady, continuous heat by transferring that heat to other objects in the room. Many gas fireplaces provide both warm air and a radiant heat surface to warm the space around them.

Direct Vent Fireplaces
Direct vent fireplaces have revolutionized fireplace placement in homes. Since they are vented directly to the outside through a whole in an exterior wall, there is no need to construct a chimney or run a freestanding flue above the roofline. Like firebox inserts, direct vent fireplaces are available in sealed combustion direct-vent models. When the fireplace is sealed, the air that is used to generate the flame (combustion air) is drawn from outside. The fumes that are a byproduct of the combustion are also vented to the outside. In this way, air contaminated with combustion byproducts and unused fuel does not circulate in the home, and household air is not used to fuel the combustion process.
A sealed-combustion direct-vent fireplace is by far the most efficient fireplace option. Since the entire operation is independent of the household air, with sealed combustion direct vent fireplaces there are no drafts and no heat loss. In fact, these fireplaces operate at a near 90
percent efficiency rate. AFUE-rated fireplaces can generate as much heat as a furnace—upwards of 40,000 Btu in some cases—and should be taken into account in any heating and cooling calculations for your home. Manufacturers offer heat calculation charts to help determine the number of Btu required to adequately heat the space in question. Armed with this knowledge, homeowners can shop for the right match in terms of capacity and aesthetics.

There are debates, however, as to the air quality generated by vent-free fireplaces. While their literature states that these fireplaces meet or exceed all guidelines for indoor air quality, there are those who insist that fresh

air must be exchanged to compensate for the room air used in combustion. Exterior ducts and improved ventilation may be required in some cases.

Ease and Comfort
Most gas fireplaces are paired with automatic controls that make enjoying a dancing flame as easy

as a flick of the switch. Handheld remotes allow homeowners to control the heat. Some even offer automatic shutoffs. One key feature is the electricity-free ignition offered by some manufacturers. With this homeowners need never worry about heat in times of power outages. More than a selling feature, electricity-free ignition ensures heat throughout the winter season, no matter what storms or winds may blow.