How to Tell If Your Gas Logs Are Vent-Free


The term hearth and home takes on new meaning when designing a fireplace. Gas fireplaces provide heat, light and beauty. Vented and vent-free logs are both used in a gas fireplace, but they act very differently. Vented logs create a large, realistic fire with dancing flames. This type of fire requires a chimney for safety. Vent-free logs do not need a chimney, but provide a smaller flame. These logs are designed to hold the heat and reflect it into the room.

  • Inspect the logs. All vent-free logs are firmly attached to a U-shaped burner and cannot be moved. If the concrete logs are loose, the logs are designed for vented use.

  • Follow the gas line from beneath the logs to where it disappears in the wall or floor. If the gas is merely contained by a simple gas line, then the logs are vent free. If there is a small cylinder attached to the gas line, then the logs are vent-free. This is called the Oxygen Depletion Sensor and is located just outside the range of the fire. It measures the oxygen in the area. Federal law mandates that all vent-free logs be equipped with an Oxygen Depletion Sensor. When the oxygen level drops, the sensor turns off the gas and stops the fire.

  • Turn on the fireplace. If the flames reach above the gas logs and the look like a wood burning fireplace, then the logs must be vented. If the flames are small, an have a blue cast, the fireplace is vent-free.

Tips & Warnings

  • Vent-free logs are designed to be more realistic, but since they must be attached to the gas burner, they are stationary and cannot be shifted.
  • Whether the fireplace is vented or vent-free, it's always a good idea to place a carbon monoxide detector in the room with the fireplace. The Oxygen Depletion Sensor is one layer of protection, but it only required on a vent-free fireplace.

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  • Photo Credit fireplace image by Ekaterina Sidorenko from
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