Vented and Ventless Gas Logs Explained

Vented Gas Logs-Napoleon

With the on-set of colder weather, we are getting many question about the difference between Vented and Ventfree. We’ve put together a little information that will help you in your buying decision.


The vented gas logs require a flu or a chimney to exhaust the toxic carbon monoxide they produce. Many of these log sets burn gas that passes through sand beneath the logs. Often vermiculite and clumps of rock wool are placed over the sand. These elements produce the highly realistic glowing embers. Vented gas logs also are capable of consuming large amounts of gas. Some can ingest up to 90,000 BTUs per hour! Unfortunately, 85 – 90 percent of this energy goes up the chimney. Fireplace dampers must be locked or clamped in the open position at all times.

Advantage-Vented Gas Logs-White Mountain Hearth

Treehouse- Vented Gas Logs-White 
Mountain Hearth



  1. Extremely realistic flame pattern that looks like a wood fire.
  2. Flame is much taller than ventless logs.
  3. Flame dances and wraps around logs like real wood.
  4. Does not require a CO2 detector.
  5. Since the damper is open, the odor will go up the chimney.
  6. Many now offer radiant heat, approximately 40-50% of heat is radiated back into the room, instead of up the chimney.

Ventfree Gas Logs- Napoleon


Ventless gas logs are technological marvels. They have special burner elements that burn gas with minimal carbon monoxide production. Vent free gas logs certified by the American Gas Association (AGA) are equipped with oxygen depletion sensors (ODS). These devices sense when oxygen in the room drops to a certain percentage. If this occurs, the sensor shuts off the supply of gas to the logs. Defective sensors fail in the safe mode. They will not allow gas to pass to the logs.

Ventless gas logs burn less gas than their big brothers. They are only permitted to burn a maximum of 40,000 BTU’s per hour. However, since your fireplace flue is closed or non existent, all of this energy is released into your house. During a power outage, these appliances can be used as a temporary heat source.


All gas logs have the capability of producing huge amounts of water vapor. 1.5 gallons of water is produced for every 100,000 BTU’s of gas burned. This massive amount of water can condense on cold chimney flue walls and drip into your fireplace. In the case of vent free logs, this water vapor can condense on windows and any other cold surfaces. Should you install these in a newer air-tight home, you may create severe moisture problems in your attic and in exterior wall cavities.


Charred Oak-Ventfree Gas Logs-White Mountain


Stacked Age Oak- Ventfree Gas Logs-White Mountain




  1. Ventless gas logs {often referred to as “Vent-Free} have specially designed burners that burn the gas cleanly and produce almost no exhaust…somewhat like the way a gas range in a kitchen works. Since there is little or no exhaust, they can be burned with the damper closed.
  2. The beauty of this type of system is that 99.9% of the heat produced by the gas logs goes into the room. However, there are many negative features commonly associated with ventless logs that you must be aware of before you decide to purchase them.
  1. Ventless gas logs will introduce excess moisture into your home which can result in mold and mildew.
  2. Ventless logs produce an odor that many people equate to the smell of burning kerosene.
  3. Ventless logs are required to have an ODS {Oxygen Depletion System} as well as a CO2 detector…which might tell you that there are some risks involved in operating them if these systems fail.
  4. The Flame pattern with ventless logs is not nearly as realistic in comparison to vented logs.

To recap:

Ventless Gas Logs

Vent free gas logs are nearly 100% efficient as they keep almost all the heat inside your home. No ventilation is necessary so they can be added to homes without fireplaces.

Vented Gas Logs

Vented gas logs are similar to a real wood flame and the chimney damper must be kept fully open during operation. The logs generally produce a more attractive, natural firelight or fireplace look.