By Barry Stone
Dear Barry,
In a past article, you recommended that fireplace dampers be permanently opened when gas logs are used. This was to prevent exhaust gases from entering the home. In my neighborhood, none of the fireplaces has dampers or chimneys. Instead, they are "ventless" gas log fireplaces, designed to vent into the living area of the home, rather than to the outside. Some people in my area have even installed ventless gas log units in their existing fireplaces and have simply closed their dampers. What is your take on this? -Dave
Dear Dave,
"Ventless" gas log units are approved in some states and strictly prohibited in others (California being an example). Many members of the chimney sweep profession are concerned about these fixtures because "ventless" is a misnomer. These fixtures should actually be called "room vented" fireplaces, since that is truly what they are. All combustion products from these fireplaces are simply venting into the rooms where the units are installed, and this poses two distinct and significant health and safety issues.
The first and most common problem with ventless gas logs is excessive moisture condensation, since one of the byproducts of gas combustion is water vapor. A potential consequence of indoor air moisture is fungus and mold infestation, a condition whose adverse health effects have been widely publicized during the past year.
The other derivative of gas combustion is carbon dioxide, assuming that optimum combustion is occurring at the gas burner. However, if combustion is incomplete for any reason (such as poor adjustment of the gas/air mixture or contact of the logs with the flame), then carbon monoxide can be produced and vented directly into the home, with the potential for disastrous results. Carbon monoxide, of course, is the main cause for concern among fireplace professionals. Accordingly, my advice is to abandon the installation and use of such fixtures.
. Questions of a Do It Yourself nature should be submitted to our "