The Problem With Oxygen Depletion Sensors…

The problem with oxygen depletion sensors is that they don’t sense oxygen.  Oxygen depletion sensors (ODS) are found on gas log appliances and are intended to shut the appliance off before the oxygen in a space falls to a dangerous level.  ODS sensors are thermocouples which produce a millivoltage when heated.  For this reason, the sensing end of an ODS sensor should be in contact with the pilot flame.  When operating properly, the flame heats the thermocouple which produces a millivoltage which in turn keeps the main gas valve open and allows gas to flow to the main burner.  When the flame cools as a result of low oxygen levels, the thermocouple or ODS fails to produce the necessary power to keep the main gas valve open and allows it to close, preventing gas flow and subsequent ignition.  The real problem however, is not low oxygen level, but the production and distribution of soot.  Anyone who has ever dealt with a soot damaged home knows how difficult the process can be to recover from the damage.  You see, appliances that burn with a yellow flame are already burning natural or propane gas incompletely.  That is, the carbon not consumed by the combustion process, will be visible and deposited as soot on clothing, furniture, draperies and appliances.   As a result, the ODS will NOT shut down the unit in time to prevent a soot production problem.  The lesson to be learned here is that even though your appliance has an ODS, don’t be fooled into thinking that you are protected.  Remember, if your appliance is designed to burn with a yellow flame, it is already producing soot.  Keep an eye on your fireplace insert, particularly if yours is unvented.  You will eventually see soot on the inside walls and if you see it there, it’s in the house!  The only way to prevent further damage is to quit using the gas logs set.

 

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Soot Damage From Gas Logs

Although it has been several years since we’ve seen sooting damage from a set of gas logs, it still occurs. The main problem is that soot is created when a fuel such as natural gas or propane is burned incompletely.  That is, there is a lack of air mixed with the gas and as a result, carbon is not completely burned.  The excess carbon then appears as soot on solid surfaces.  Appliances, like gas logs units, that advertise the appearance of a realistic wood fire tend to burn with a yellow flame.  The yellow flame is an indication that the fuel is not burned completely.  Some older readers might remember when gas appliances, including log sets, were made to burn with a blue flame.  A blue flame indicated that your appliance was operating as efficiently as possible.  When the flame turned yellow, this was owner’s cue to have the appliance checked.  This is no longer true and hasn’t been true for at least 30 years.  As a result, homeowners don’t have any warning as to when their appliances need attention.  Many of the log sets made today come equipped with what is known as an oxygen depletion sensor.  The device is supposed to shut the log set off if the oxygen in the space drops to a point below what is required to operate the set.  In reality, soot can be produced before the oxygen level drops to an unacceptable level.  This is because the sensor does not sense oxygen, it senses heat from the pilot.  As long as the pilot is producing a flame and the sensor is detecting the heat, the main gas valve will remain open.

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