- Description The JXi Natural Gas Heater sets a new standard in pool and spa heating technology with its ultra-compact size and its innovative, lightweight design. Made for Aussie conditions, the JXi 200MJ will give you the warmth you want whenever you want it. Available in 2 sizes: 200MJ and 370MJ. Features: 83% thermal efficiency rating and low-NOx design surpasses strict DOE Energy Efficiency requirements. Fits 61cm × 61cm pad and only weighs 57kg or less. 180° rotatable top negates the need for additional plumbing, saving the pool owner additional money. Digital interface for effortless temperature control and diagnostics with run-time and cycle metre.