Venting Issues for Vented Fireplaces The fireplace must exhaust all of the products of combustion
All vented pan burners will produce soot, therefore a vented gas log set does not correct a “smoking fireplace” (one in which smoke and soot enter the living space). The most telltale sign of a smoking fireplace is a blackened fireplace face immediately above the fireplace opening.
There are only two places for the soot and other products of combustion to go: (1) up the chimney, or (2) into the room. The gas log set does not influence where it will go Potential reasons for soot going into the room include:
- Damper not open or not open far enough.
- Too small of a flue.
- Too large of a fireplace opening in comparison to the flue opening (1/10 rule. For masonry chimneys, most codes require that the area of the flue be no less than 1/10 of the area of the fireplace opening. Metal chimneys can exhaust well with smaller flue size.).
- Obstruction in the chimney. Bird nest, creosote build-up, etc.
- Negative room pressure created by kitchen exhaust fans, ceiling fans, etc.
- Log set installed too close to the opening. The combustion products are spilling out of the opening into the room.
- Air flows outside the house that do not promote proper draft. May require lengthening the chimney stack or the installation of a chimney cap.
- Chronic “smoking fireplace”. Fireplace design related.
- Chimney “cold block” that inhibits air flow up the chimney.
Use of the gas log set (or wood burning, for that matter) should cease until the source is identified and corrected. Failure to do so may result in harm to life and property. If unable to correct the smoking condition, the only gas log set that can be safely used is a vent-free gas log set (such as the Rasmussen Chillbuster series), which are certified to ANSI Z21.11.2, the national unvented heater standard. This standard is the most restrictive of all gas appliance standards. This standard does not permit sooting and allows the lowest level of carbon monoxide of all gas appliances.