1.   But they are not quite as energy efficient as ventless fireplaces, and their flames are not as dramatic as vented fireplaces.

2.   Cooper said the manufacturers of ventless fireplaces suggest that people using them crack a window in the room to bring in oxygen and allow combustion byproduct gases to escape.

3.   Day said a ventless fireplace should produce an even blue flame, and the presence of any soot is an indication of potentially serious problems.

4.   He said burning fuel always produces byproducts, but ventless fireplaces are designed to burn their fuels as completely as possible so potentially harmful byproducts are minimized.

5.   No fire burns without consuming oxygen, and a ventless fireplace in a tightly closed room could reduce the available oxygen in the air to dangerously low levels.

6.   Since no waste gases are vented outside, practically all the heat a ventless fireplace produces stays in the room.

7.   Stegman said ventless fireplaces are equipped with oxygen depletion sensors that cut off the flames when the oxygen in a room drops below a certain level.

8.   The big sellers now are ventless fireplaces.

9.   The flames may not be as impressive as vented models, however, and ventless fireplaces raise some safety concerns.

10.   Ventless fireplace manufacturers suggest that people using them crack a window in the room to bring in oxygen and allow combustion by-product gases to escape.