How Dangerous Are Ventless Gas Fire Places?


Ventless gas fireplaces with Oxygen Detection Safety-pilot (ODS) devices have been in the American marketplace since 1980. Safety records show that since that time, there have been no documented deaths due to emissions from ventless fireplaces.


  • One reason people install gas fireplaces is to have a source of heat in case of electrical power outage. A ventless fireplace is often a replacement for a wood burning or electric fireplace or an upgrade for an older gas log fireplace. Ventless systems are commonly used as supplemental heat sources. In warmer regions of the U.S.,ventless units may be the main heat source.


  • There have been three major kinds of gas fireplaces in use in the U.S. The oldest kind used open gas flames as the direct heat source, sending dangerous fumes up the chimney; they were very inefficient sources of heat.

    The older vented gas logs emitted dangerous levels of carbon monoxide and required adequate ventilation. Although very realistic looking, they were not environmentally friendly.

    Dangers of the old gas fireplaces have been remedied. The new ventless gas fireplaces are extremely energy efficient. They have been designed to burn fuel completely, providing much greater heat output. No vent is required because the burners are designed to leave no dangerous substances in the air. An advanced automatic shut-off valve cuts the gas supply if a problem should occur.

    Ventless fireplaces are designed for either propane or natural gas. Their pilots are not interchangeable. The pilot cannot be adjusted and it will disintegrate if any attempt to modify it is made. Tampering is dangerous and will result in automatic gas shutoff and automatic shutdown of the ignition.


  • Vent-free gas fireplaces are 99.9 percent energy efficient in their combustion. With no need for a chimney or hole through the wall, there is no heat loss or air leak. A vent-free fireplace can be placed almost anywhere in the house where there is a gas line. However, most states restrict their use in bedrooms.

    Every vent-free unit sold in the U.S. has an Oxygen Detection Safety-pilot. The ODS consists of a precision-engineered pilot burner that monitors the oxygen level in the air. It also has a thermocouple and safety shut-off valve. If the oxygen level falls below a set minimum, the flame is extinguished, causing the thermocouple to cool and close the gas valve. The unit cannot be used again until there is proper ventilation and the valve has been opened and the pilot relit.

    Matches are not necessary; there is an ignition device to light the pilot. A preset internal gas pressure regulator eliminates the possibility of dangerous overfiring. Fireplace units are complete with safety hoods and fire screens.


  • Environmentally friendly ventless gas fireplaces are clean burning and give off no fumes. They are affordable to purchase, install, and operate. A ventless fireplace adds to the resale value of a home.


  • Even with the documented safety record, some people feel that there is a risk, however small, that the ODS might fail.

    The more likely problem is water condensation. Gas naturally gives off water vapor during combustion, and this occurs with the vent-free products. Water vapor can reduce the need for a humidifier, but excess vapor may condense inside windows and walls. There is a potential for mold and mildew.

    As with any heat source, combustible materials must be kept at a safe distance.

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