An Ultra Low NOx gas water heater is one that emits a lower level of nitrogen oxide than a standard gas water heater. Some states and municipalities have requirements and standards to limit the maximum amount of NOx emissions for gas water heaters – particularly certain counties in California and in the state of Utah. Our Ultra Low NOx models are designed to comply with these standards. To find out what is required for your area, we recommend you contact your plumbing professional who knows the local codes and regulations. Need a pro? Find one here.