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Ventless Propane Gas Log Fireplaces - Benefits plus Dangers to Health and House

Updated on January 21, 2011

Benefits and operation of the ventless propane gas firelog

Advances in gas firelog technology have resulted in ventless units. They require no vent, no chimney. All the heat produced in combustion flows into the room and warms the air. it is much more efficient that a vented propane gas firelog, where much of the heat is wasted up the chimney.

All gas log fireplaces with a pilot light should include a thermocouple that senses whether or not the pilot light is on or off. The thermocouple automatically shuts off the gas whenever the pilot light is goes out.

Vent-free firelog units are designed with extra safety standards. An oxygen sensor detects the level of oxygen near the unit. If for any reason oxygen drops to a pre-set safety level, the firelog unit will shut down.

So that the flames burn as clean as possible, the firelog unit is designed so that flame contact with ceramic logs is eliminated or minimized

New ventless firelog units are beautifully designed to suit many decors.

Dangers of vent-free propane combustion

As long there is plenty of oxygen in the room with a propane gas firelog, the burning propane produces carbon dioxide (CO2), water (H2O) and heat. If there is insufficient oxygen, the propane combustion is incomplete and the burn also produces carbon monoxide (CO) and carbon (C) -- or soot. That is why a ventless firelog MUST have an oxygen sensor. That is also why the room MUST be large enough to provide sufficient oxygen for combustion, and why it is recommended that a window be opened when the firelog is burning.

It is also highly recommended that a separate carbon monoxide sensor be installed in the room with the firelog. In the event that there is problem with the oxygen sensor, the alarm will be a warning.

The propane in your tank may not be 100% pure propane. It may contain impurities and a odorant to give it a distinctive smell. To the extent it is not 100% propane it may not burn "clean."

The oxygen sensor in the firelog can malfunction. So can the room carbon monoxide detector. Both should be inspected periodically to assure that they are operating properly. The firelog unit should be checked annually by a qualified techician.

The ventless firelog should be designed to minimize flame contact with surfaces that, when hot, add contaminants to the hot gases produced during combustion. If for some reason, the firelogs are disturbed or rearranged, there many be more contaminants produced.

Combustion and heat may burn off pre-existing soot on fireplace walls or the closed damper, if the unit is placed in masonry fireplace previously used for wood fires.

One of the most common complaints about vent-free firelogs is the soot that dirties everything in the room and home.

Finally, the normal operation of the vent-free firelog adds a lot of water vapor to your room and home. Whether or not it produces mold depends on the relative humidity in your home.

Safety and regulation of ventfree propane gas firelogs

The American National Standards Institute (ANSI) issues standards for the manufacture of ventfree firelogs under publication Z21.11.2 and its updates. ANSI is a private non-profit organization that oversees the development of voluntary consensus standards for products, services, processes, systems, and personnel in the United States. The organization also coordinates U.S. standards with international standards so that American products can be used worldwide.

ANSI includes a disclaimer in ANSI pub Z21.11.2 about ventfree gas heaters:--

"This publication represents a basic standard for safe operation, substantial and durable construction, and acceptable performance of gas-fired unvented room heaters. It is the result of years of experience in the manufacture, testing, installation, maintenance, inspection and research on appliances designed for the utilization of gas. There are risks of injury to persons inherent in appliances that, if completely eliminated, would defeat the utility of the appliance. The provisions in this Standard are intended to help reduce such risks while retaining the normal function of the appliance." (italics added)

ANSI Z21.11.2a also warns that:--

"Safe and satisfactory operation of a gas-fired unvented room heater depends to a great extent upon its proper installation, use and maintenance. It should be installed in accordance with the National Fuel Gas Code, ANSI Z223.1/NFPA 54; manufacturers' installation instructions and local municipal codes." (italics added)

Some state and local codes in the U.S. prohibit unvented room heaters due to their inherent risks. If you are considering purchase of a vent-free firelog unit, be sure to:--

  • check with your local and/or state building code administration to see whether (1) a ventfree firelog unit is allowed in your home, and (2) if allowed, what standards govern its use
  • consult with your dealer and be sure the unit you buy is fully compliant with applicable building code and ANSI standard Z21.11.02.
  • make sure that it is properly installed
  • make sure you understand and follow all safety precautions.

Do you have a ventfree propane gas firelog? How do you like it?

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    • profile image

      jessica 

      6 years ago

      we just moved into our home and have a vent free gas log fireplace... we love it except for the smell it puts off. are we burning it wrong, or is there somethihg wrong with it, or is that just the way they burn...??

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