ODS stands for “Oxygen Depletion Sensor" a term which accurately describes this valve type. The valve itself is similar in many ways to the two valve types above...with one exception. The pilot tube is a precision mechanism that creates a very stable flame as long as the room air contains the proper amount of oxygen. If the oxygen level in the room air drops even slightly, the pilot becomes unstable and lifts off of the thermocouple (see diagram) causing the gas valve and appliance to cease operation. This type of valve is very reliable, and there have been very few failures of this system - even with tens of millions in use worldwide.

Normal Operation:
20.9 Percent Oxygen - The flame touches the tip of the Thermocouple, generating the necessary millivoltage needed to hold the gas valve open.

Oxygen Level Drops:
19 Percent Oxygen - The flame begins to lift off the precision Pilot Burner. The Thermocouple begins to cool.

Safety Shutdown:
18 Percent Oxygen - The unstable pilot flame goes out, causing the Thermocouple to cool. The Thermocouple stops generating the electricity needed to hold the spring loaded solenoid valve open. The valve shuts the ventfree gas heater down and cannot be started until the oxygen level in the room returns to normal.

LET’S CLEAR THE AIR
To document how vent-free gas products affect indoor air quality, the American Gas Association Research (AGAR) Laboratories* performed an extensive, independent scientific study.

The study was performed in a real home, the AGAR research and demonstration house. AGAR scientists tested the levels of all five major contributors of indoor air quality – oxygen, carbon monoxide, carbon dioxide, nitrogen dioxide, and water vapor (humidity) – against the latest IAQ guidelines and recommendations. The chart below shows the results of the study. The researchers concluded that, in all cases, vent-free gas heating products performed well within nationally recognized guidelines for indoor air quality. Vent-free gas products provide clean heat.

* AGAR was the research arm of the International Approval Services (IAS), a nationally recognized independent testing agency. IAS, formerly known as A.G.A. Laboratories, now known as CSA International, has been certifying gas appliances since 1928 to ANSI safety standards. In 1997, AGAR was purchased by Energy International, Inc