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Indoor fireplace venting

Gas fireplaces need to be properly vented to the outdoors. Venting choices include gravity vented, direct vented and power vented. Log set fireplaces must be gravity vented.

Gravity (natural draft) venting

A gravity-vented fireplace draws the air it needs for combustion from the room in which it is installed. As hot air rises, the gravity vent takes advantage of the natural draft caused by the flames, to expel the products of combustion to the outside.

With a gravity-vented fireplace:

  • Hot air rises to exhaust products of combustion out of the building.
  • It’s often installed in an existing chimney cavity using a flexible chimney liner.
  • It is sometimes installed with a sheet-metal chimney liner.
  • Some heated room air can be lost as it d​raws combustion air from the room.


An alternative to utilizing an existing chimney is to use a B-vent. A B-vent is also a gravity venting system, but has concentric pipes – an inner pipe, which allows hot gases to escape, and an outer pipe, which provides a buffer of cooling air. The space between the inner and outer pipes can be insulated or be a stagnant air area. Do not confuse this with direct-vent piping.

With a B-vented fireplace:

  • The double wall design allows the vent to be installed close to combustible surfaces and materials.
  • It can be installed without masonry or a fireplace structure.
  • It uses the principle of “hot air rises” to exhaust products of combustion out of the building.
  • Some heated room air can be lost with a B-vented fireplace as it draws combustion air from the room.

Direct venting

These fireplaces don’t require a chimney and can be installed on any outside wall. Venting can then be run for a limited distance through the wall or roof.

With a direct-vented fireplace:

  • The “sealed combustion” design is heat and energy efficient because the unit doesn't use room air for combustion or lose warm room air via the vent.
  • No products of combustion spill into the home, ensuring good indoor air quality.
  • Direct venting offers unlimited installation options for renos and new construction.

Power venting

Power venting is used where the combustion by-products have farther to travel or where gravity or direct venting is impractical for structural reasons.

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