What Makes A Ventless Gas Log Safe In An Unvented Fireplace?

by grillrepair on August 6, 2011

Vent-Free gas log fireplace kit with push-button on and off controls

Vent-Free gas log fireplace kit with push-button on and off controls

This Vanguard ventless gas log fireplace is not the kind of vent-free fireplace we stock any longer because of the distribution availability here in Florida.  However, the Vanguard vent free gas log fireplace design is a good example of “common” ventless gas fireplace designs.

This is the unvented gas fireplace burner and infrastructure.  As you can see the valve, burners, log supports,

ventless gas log fireplace burner without logs to show the support designs

ventless gas log fireplace burner without logs to show the support designs

decorative grates, fireplace igniter and regulators are all one solid item.  Unlike the vented gas log fireplace kit designs, unvented gas fireplace kits have almost nothing to build or assemble.  Because of the strict rules and building codes that regulate ventless gas fireplaces that are designed for indoor use without a chimney the manufacturers usually attach the parts and pieces so the only attachment the installer has to preform is the gas line.  Attaching a gas line to a ventless gas fireplace burner is like attaching a water-hose.  The fittings must be wrapped with teflon tape before screwed together.

Other than the different design what is it that makes a vent-free gas log certified for us outdoors without ventilation, without a chimney?  A gas log fireplaces going into a fireplace firebox with a chimney can be as simple as a rectangular pan with a single pipe-burner running across the pan.  By comparison the ventless gas log burner in the picture above is very complex.  The valve is mounted under the burner as a part of the whole design of the burners and the regulators are mounted as it is not possible to run the burner without the proper regulation for the fuel type.

The valve is designed to never pull more than forty-thousand BTU’s of gas.  Although the definition of BTU (british thermal units) refers to an actual measurement of heat barbecue grill and fireplace companies do not publish specifications in this way. Heat can be measured in calories because fuel consumed causes heat whether it is “burning” due to your body’s metabolism or “burning” in a car.  Heat can be measured in terms of joules or, more frequently kilojoules which refers to heat generated by friction: braking train wheels, brake pads on a car or even when you run your hands together quickly.  This kind of heat is measured as kilojoules.  BTU is a measurement not based on friction or fuel consumption but actual heat.  A BTU is the amount of heat needed to  raise on pound of water one degree in one hour.  BBQs and fireplace companies are actually publishing caloric heat measurements because they are measuring the amount of gas being pulled through the orifice.  In theory if all variables are consistent the amount of fuel consumed will be an adequate measurement of how much heat is generated.

The problem with this theory is that unvented gas fireplaces are designed to burn “cleaner” than a regular vented fireplace because certification is based on minimizing the flame production of particles in the air that, unvented can make us sick.  Take a small pocket lighter burning butane and hold the lit flame against a wall or any solid object and the flame will leave a black spot.  Burning gas will always produce carbon when the flame contacts a solid object.  The carbon becomes carbon monoxide in our air.  For this reason part of the certification of vent-free gas

ventless gas log fireplace side view to show burners and logs

ventless gas log fireplace side view to show burners and logs

logs check particle emmissions in the air while the fireplace burns.  Gas fireplace manufacturers eliminate most of these carbon emmissions by minimizing the contact of flames with the faux ceramic or foam logs.

Notice in the side-view image of this Vanguard vent-free gas log fireplace set there are only 3 logs.  This vanguard burner has a front burner a back burner and a cross-over burner connecting the two burners.  The 3 pieces of architectural foam made to mimic the look and feel of wood logs.  The logs and the row of flames look like stripes because the flames are actually raising and flickering between the rows of flames.  This design makes the flames rise without touching the foam logs.  The heat from the flames is more intense than the btu rating would otherwise imply because the flames are burning very efficiently

All gas log fireplaces will have a thermocouple and a pilot.  The safety valve on a fireplace rests in a closed position that does not allow gas to flow through the valve.  When we light the fireplace we have to turn the control knob and then push the knob in.  Once turned a bit the valve stem can sink in about an inch to push the valve open.  While holding the control knob pushed in we can light the pilot flame.  Normally this will happen very fast but if the gas log is new or has not been used in more than a month lighting the pilot can take as much as five minutes.  Once the pilot is burning you can notice there is a cylindrical shape mounted to be in the pilot flame.  This is the thermocouple.  When heat is transferred through the thermocouple it generates a small millivolt electrical charge.  The electrical charge travels through a copper line to the safety valve.  At the end of the thermocouple copper line is a piece of steel that becomes a magnet once the electric charge travels through the copper.  Once the heat has created a magnetic charge the valve will be held open by the magnet mounted inside the safety valve getting pushed open by the reverse terminal magnet charged by the thermocouple.  Now we can release the valve without the pilot going out.

Most manual gas log fireplace valves will have an “on” position beyond the “pilot”position so once the valve is holding itself open and is able to allow gas flow turn the valve to “on” and enjoy the fireplace.

Finally, all vent-free gas log fireplaces will also have a ODS mounted somewhere.  Usually attached to the pilot because it is easiest to disrupt gas flow by disrupting the magnetic charge an Oxygen Depletion Sensor reads particles in the air in order to stop gas flow if the flames are consuming dangerous levels of oxygen.  The oxygen depletion sensor is like a safety net that makes sure there are safe, clean levels of oxygen around the fireplace so no one gets sick from the ventless burner burning too dirty.  Many people try to manipulate their unvented gas log by adding different or more logs or accessories that change the flame pattern.  The ODS will stop the fireplace from becoming dangerous.  It is safe to add ember-glow stuffing and other related accessories to make the ventless gas log fireplace look more realistic, more rustic or more contemporary but we cannot manipulate the flames without taking the safety features into consideration.

For more information about vent-free gas logs check us out at www.grill-repair.com or call us at 954.247.4552.

stainless steel vent free gas log fire glass fireplace burner with copper glass

stainless steel vent free gas log fire glass fireplace burner with copper glass

Contemporary ventless gas logs with alternative designs utilizing fire shapes, fire balls, fire stones and fire glass are also available for safe modern design fireplaces hearths.

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