Proper Ventilation for Gas Fireplaces

The Direct Vent Option

• Gas-fired, direct vent fireplaces feature an exhaust pipe measuring 4 inches in diameter enclosed within a 7-inch diameter pipe. The larger pipe supplies outside air to fuel combustion while the smaller, inside pipe carries fire-produced contaminants to be released outside of the home. Venting may be configured out the top or through the back of the firebox. For homes constructed without a chimney, direct venting is a quick and affordable option.

B-Vent Fireplaces

• In B-vent fireplaces, combustion is supported by air drawn from the room in which the fireplace sits. The 4-inch B-vent pipe is therefore used strictly for exhaust purposes. In chimney-vented models, a relatively inexpensive liner may be used. If venting will be directed through a wall and then upward through the roof, a higher gauge, pricier venting material must be provided. A B-vent gas fireplace allows for more choice in positioning as an outside wall is not always required.

Pros and Cons of Vent-Free Installations

• In vent-free fireplaces, the flame is fed through a permanent line connected to a ceramic plaque or burner located within the fireplace. The fireplace may be positioned anywhere in your home. Indoor air quality may be adversely affected by combustion byproducts that remain inside rather than carried outside. Humidity levels, carbon monoxide and nitrogen dioxide levels may increase, and oxygen levels may decrease.

Vent-Free Safeguards

• An oxygen detection safety pilot (ODS), mandated for use in vent-free gas heating appliances since 1980, will automatically turn off the fuel if fireplace-centered combustion uses too much oxygen and reduces the level within your home to below 18 percent. Running a dehumidifier can control overly-elevated humidity levels. All homes outfitted with gas fireplaces should also have smoke detectors and carbon monoxide detectors in place to ensure the safety of all occupants. Consult your local fire prevention association for additional guidelines.