A direct-vent fireplace will use outside air for combustion, thereby increasing efficiency and eliminating the need for opening windows Photo courtesy of Hearthmasters, Inc.while its in use, says Padgitt.

Many homeowners end up asking chimney sweeps to take out their vent-free gas logs due to problems they find associated with the appliance. Often, a homeowner will report a horrible odor when the logs are in use, water running down the windows and walls, stains and soot, mold and mildew issues, unexplained headaches and being ill while in the house while using the logs.

When burning gas, several by-products of combustion are produced: Carbon monoxide, carbon dioxide, nitrogen dioxide, formaldehyde and significant quantities of water.

Direct vent fireplace venting uses a coaxial pipe system (small pipe within a large pipe) and draws combustion air from the outside through the outer pipe. Some of its features are: The inner pipe vents the exhaust while the outer pipe draws in the outside air, can either vent out the top or out the back, for installation versatility, can vent horizontally through an outside wall, or vertically through the roof .- no chimney required!, convenient to install, space-saving depth. but requires finishing such as a mantel and surround.

This type of fireplace venting uses economical B-vent pipe for a chimney. Some of its features are: uses room air for combustion and venting terminates above the roofline (like a furnace), more decorative, but lower efficiencies, zero clearance to combustibles, ideal for locating anywhere in the home where B-vent can be installed.

A vent-free gas fireplace operates without a chimney, flue or vent, so you can install one just about anywhere. Modern vent-free gas fireplaces: inexpensive and have low operating costs, 99% energy efficient provide warmth during power outages, do not exceed 40,000 Btu/hr of heat output.