GAS VENTING TERMS EXPLAINED  Gas appliances offer venting options that make it easy to install a fireplace or stove nearly any where you can dream of. When considering installing a gas appliance, consider the venting options that are open to you in choosing the right appliance for the right job. In historic homes it's preferable to upgrade the existing fireplace if possible, and this will add considerable resale value to your home. Upgrading existing fireplaces and old chimneys will require the talents of an experienced chimney professional; we can often help locate chimney craftsmen across the US.     Installing a new fireplace or stove is an easier task that may be done by other tradesmen. Always use the services of the most experienced and qualified technician you can find. Gas lines should only be run by licensed plumbers or HVAC technicians (check your local area requirements). When searching for a chimney sweep or fireplace installer, ask if they are members or are certified by the National Chimney Sweep Guild or the Hearth Products Association.    DIRECT VENT Direct vent fireplaces have more versatile installation options, including a horizontal vent. Using a double wall pipe, combustion air enters the fireplace through the outer chamber and exhausts through the inner chamber. Direct vent systems use a glass window because it is a sealed system. NATURAL VENT B-vent (Natural Vent) stoves use room air for combustion and send exhausts up the chimney. B-vent chimneys must run inside the house and exit the roofline, or can be installed inside of an exterior chase if installed at an outside wall.  Some natural vent appliances use a glass front and some don't. If they do use glass then you cannot remove it; if the appliance doesn't use glass then you usually can't add glass. VENT-FREE Vent-free stoves require no vent. Combustion air comes from inside the house and fumes exhaust inside your home. Many people can't tolerate the odor.    Generally, vent-free (unvented, ventless) appliances do not use glass.