The ODS or Oxygen Depletion Sensor is a pilot assembly including a thermocouple that is attached in a way that is not adjustable and operates in a fixed position. This pilot can only operate when the oxygen level in the room is at least 18%. Normally at sea level our atmosphere will contain an oxygen level of about 21% and at higher elevations above 2500 ft. this will drop to 19%-20% and may cause the pilot to shut off due to the lack of oxygen.

How this all operates is by the thermocouple responding to changes in the pilot flame characteristics and, when heated, generates a small current of electricity measured in millivolts, which keeps the gas supply valve in the open position. In the rare instance that the room oxygen level approaches ANSI defined minimums, the flame extinguishes. The loss of flame causes the thermocouple to cool. This cooling reduces the millivolt reading, which causes the gas valve to return to its normally closed position, thus turning off the fuel supply to the appliance.

The unit will not operate until the living space is properly ventilated and adequate oxygen is introduced, and the appliance is manually restarted. So you can see that the ODS is a safe and reliable device that assures your family that your vent-free gas fireplace will operate properly.

Note:  It is not recommended to install vent-free appliances as a primary heat source above 5000 ft. because of pilot outages.