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 (NO?), two oxides of nitrogen that most affect pollution. Low NOx heaters produce less harmful emissions than regular heaters and are ideal for any application. Brand: Raypak Manufacturer Part Number: 9241 Assembled Product Dimensions (L x W x H): 38.00 x 31.00 x 29.00 Inches