Raypak digital heaters have an electronic ignition, a digital thermostat and Polymer headers. They are gas powered and suitable for use with swimming 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. Cupro-Nickel refers to the fin tube heat exchanger. Cupro-Nickel heat exchangers are an excellent choice because they resist the corrosion associated with bad and fluctuating water chemistry.