Jandy Pro Series JXi 400K BTU Low-NOx Natural Gas Swimming Pool and Spa Heater - JXI400N Energy-efficient - 83% thermal efficiency rating and low-NOx design surpasses strict DOE energy efficiency requirements. Ultra-Compact Lightweight Design - Easy to store, transport, and install, the JXi is 38% lighter with a 28% smaller footprint. Smaller footprint compared to major competitor models Flexible Installation - 180 rotatable top so you never need to rotate headers. Versa Plumb-Ready - Installation in the Versa Plumb system reduces plumbing costs and increases energy efficiency, all using the smallest footprint available. Sweep elbow included in all JXi models