Sta-Rite SR333HD Max-E-Therm Black Heavy Duty Pool and Spa Heater, 333-BTU Lightweight - Lightest heater in its class Compact Design - Ideal for retro-fit installation Lower Operating Costs - 84% efficiency rating - rated 1st in its class for highest energy efficiency Rustproof Housing Sleek, matte black enclosure is made of Dura-Glass - an exclusive Sta-Rite material that handles the heat and weathers the elements