An Ultra-Compact and Energy-Efficient Gas Pool Heater The JXi™ heater sets the standard in pool and spa heating with unsurpassed energy-efficiency and optional cost-saving Integrated Bypass technology that diverts water flow away from the heater when there is no call for heat. Boasting an 84% thermal efficiency rating and a low-NOx design, the JXi is available in both natural and propane gas models. The JXi also features advanced automation compatibility with AquaLink® systems and iAquaLink™ control, for anytime, anywhere convenience, and an ultra-compact, lightweight design, that allows for faster and easier installation—making it a top choice for pool professionals and pool owners everywhere.