When shopping for an energy-efficient gas fireplace, ask for the EnerGuide Fireplace Efficiency (FE) ratings of the fireplaces you are interested in. Using this information, narrow your choices to the fireplaces that have relatively high efficiencies and can supply the kind of heat output needed for the location you have chosen.
The most energy-efficient gas fireplaces have many of the following features:
Figure 13. Typical Characteristics of an Efficient Direct-Vent Gas Fireplace
Source: Natural Resources Canada (NRCan) - Office of Energy Efficiency