ASME rated heaters are intended for use when local codes mandate the use of ASME-certified equipment in commercial installations, such as apartment, condominium and public pools and spas. NOx jointly refers to nitric oxide (NO) and nitrogen dioxide (NO2), two oxides of nitrogen that most affect pollution. Low NOx heaters produce less harmful emissions than regular heaters and are ideal for any eco-friendly application. The Raypak commercial digital heater is factory equipped with ASME waterways for commercial use and comes with a microprocessor based thermostat control. This allows the user to set the pool or spa temperature at a precise temperature using the up or down button. The digital display provides a constant reading of the pool's water temperature.